kernel-atmdd.patch

diff -urN linux-5.9/drivers.org/atm/atmdd.c linux-5.9/drivers/atm/atmdd.c
--- linux-5.9/drivers.org/atm/atmdd.c	1970-01-01 01:00:00.000000000 +0100
+++ linux-5.9/drivers/atm/atmdd.c	2020-11-03 13:31:48.120071319 +0100
@@ -0,0 +1,920 @@
+/*
+#######################################################################
+#
+# (C) Copyright 2001
+# Alex Zeffertt, Cambridge Broadband Ltd, ajz@cambridgebroadband.com
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License as
+# published by the Free Software Foundation; either version 2 of
+# the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+# MA 02111-1307 USA
+#######################################################################
+# Notes:
+# 
+# This is an example atm driver.  It does not require any actual ATM
+# hardware.  It supports AAL5 and AAL0.  frames are merely looped back
+# to the sender on the same VC they were sent.
+# 
+#######################################################################
+*/
+
+/*############ Includes ###############################################*/
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/atm.h>
+#include <linux/atmdev.h>
+#include <linux/skbuff.h>
+#include <linux/init.h>
+#include <linux/netdevice.h>
+#include <linux/sched.h> /* for xtime */
+
+/*############ Defines ################################################*/
+
+#define MYATMDD "atmdd"
+#define KLOG_PREAMBLE MYATMDD ": "
+#define MYATMDD_VPI_BITS 1     /* Allow ?.1.? but not ?.2.? */
+#define MYATMDD_VCI_BITS 11    /* Allow ?.?.2047 but not ?.?.2048 */
+#define MYATMDD_PCR 100000
+#define RXQ_SZ 16
+#define TXQ_SZ 16
+#define AAL5_MTU (1510+8) /* Default AAL5 Maximum Transmission Unit (and length of AAL5 buffers) */
+#define AAL5_BUFLEN (((AAL5_MTU + 47)/48)*48) /* Round up to n*48 bytes */
+#if 0
+# define DEBUG(format,args...) printk(format,##args)
+#else
+# define DEBUG(format,args...)
+#endif
+/*############ Types ##################################################*/
+
+/* status flags shared between s/w and emulated h/w */
+typedef enum {
+    RX_EMPTY, /* No sk_buff present */
+    RX_FULL,  /* sk_buff present and awaiting data */
+    RX_RECVD, /* sk_buff present and contains valid data */
+} myatmdd_rxstatus_e;
+
+/* status flags shared between s/w and emulated h/w */
+typedef enum {
+    TX_EMPTY, /* No sk_buff present */
+    TX_FULL,  /* sk_buff present and awaiting transmission */
+    TX_SENT,  /* sk_buff present and has been sent */
+} myatmdd_txstatus_e;
+
+typedef struct {
+    struct sk_buff **start;
+    struct sk_buff **end;
+    struct sk_buff **head;
+    struct sk_buff **tail;
+
+    /* everything below this line emulates h/w */
+    myatmdd_rxstatus_e *status;
+    struct sk_buff **hw_ptr;
+    int *pkt_len;
+
+} myatmdd_rxq_t;
+
+typedef struct {
+    struct sk_buff **start;
+    struct sk_buff **end;
+    struct sk_buff **head;
+    struct sk_buff **tail;
+
+    /* everything below this line emulates h/w */
+    myatmdd_txstatus_e *status;
+    struct sk_buff **hw_ptr;
+    int *pkt_len;
+
+} myatmdd_txq_t;
+
+typedef struct {
+} myatmdd_devdata_t;
+
+typedef struct {
+    myatmdd_rxq_t rxqueue;
+    myatmdd_txq_t txqueue;
+} myatmdd_vccdata_t;
+
+/*############ Module paramters #######################################*/
+
+MODULE_AUTHOR("Alex Zeffertt, ajz@cambridgebroadband.com");
+MODULE_DESCRIPTION("Example ATM device driver (loopback)");
+#ifdef MODULE_LICENSE
+MODULE_LICENSE("GPL");
+#endif
+/*#################### Forward declarations ###########################*/
+
+static void myatmdd_emulate_loopback_hardware(struct atm_vcc *vcc);
+
+static void myatmdd_free_tx_skb(struct sk_buff *skb);
+
+/* these functions will need modifying in a real ATM driver */
+static void myatmdd_rx_interrupt(struct atm_vcc *vcc);
+static void myatmdd_tx_interrupt(struct atm_vcc *vcc);
+
+/* functions for manipulating circular bufs */
+static int myatmdd_init_rxq(myatmdd_rxq_t *queue, int size);
+static int myatmdd_init_txq(myatmdd_txq_t *queue, int size);
+static int myatmdd_release_rxq(myatmdd_rxq_t *queue);
+static int myatmdd_release_txq(myatmdd_txq_t *queue);
+static int myatmdd_txq_enqueue(myatmdd_txq_t *queue, struct sk_buff *skb);
+static int myatmdd_rxq_enqueue(myatmdd_rxq_t *queue, struct sk_buff *skb /* empty buffer */);
+static struct sk_buff *myatmdd_txq_dequeue(myatmdd_txq_t *queue);
+static struct sk_buff *myatmdd_rxq_dequeue(myatmdd_rxq_t *queue, int *pkt_len);
+
+/* myatmdd_ops registered by ATM device */
+static int myatmdd_open(struct atm_vcc *vcc);
+static void myatmdd_close(struct atm_vcc *vcc);
+static int myatmdd_ioctl(struct atm_dev *dev, unsigned int cmd,void *arg);
+
+
+static int myatmdd_send(struct atm_vcc *vcc,struct sk_buff *skb);
+static int myatmdd_change_qos(struct atm_vcc *vcc,struct atm_qos *qos,int flgs);
+static int myatmdd_proc_read(struct atm_dev *dev,loff_t *pos,char *page);
+
+/* myatmdd_phy_ops registered by phy driver */
+static void myatmdd_phy_int(struct atm_dev *dev);
+static int myatmdd_phy_start(struct atm_dev *dev); /* <-- This is the only thing exported by PHY driver */
+static int myatmdd_phy_ioctl(struct atm_dev *dev,unsigned int cmd,void *arg);
+
+/*#################### Global scope variables #########################*/
+
+/* operations registered by the atm device */
+static const struct atmdev_ops myatmdd_ops =
+{
+	open:        myatmdd_open,
+	close:       myatmdd_close,
+	ioctl:       myatmdd_ioctl,
+
+
+	send:        myatmdd_send,
+	change_qos:  myatmdd_change_qos,
+	proc_read:   myatmdd_proc_read,
+    owner:       THIS_MODULE,
+};
+
+/* operations registered by the phy driver */
+static const struct atmphy_ops myatmdd_phy_ops = {
+	start:      myatmdd_phy_start,
+	ioctl:      myatmdd_phy_ioctl,
+	interrupt:  myatmdd_phy_int,
+};
+
+struct atm_dev *myatmdd_dev;
+
+/*#################### Function definitions ###########################*/
+
+
+/*
+#########################################################
+#
+#  Function : myatmdd_rx_interrupt, and myatmdd_tx_interrupt
+#             
+#  Purpose  : handle interrupt from hardware.  In first 
+#             case this means extract recvd buffers and pass
+#             it up protocol stack.  In 2nd case this means
+#             free the sent buffers.
+#             
+#  Args     : pointer to private data of the VCC concerned
+#             
+#  Returns  : nowt
+#             
+#  Notes    : 
+#             
+##########################################################
+#  Edit history:
+#  Who     When    What
+#  AJZ     10Apr03 Created
+##########################################################
+*/
+
+static void myatmdd_rx_interrupt(struct atm_vcc *vcc)
+{
+    struct sk_buff *skb;
+    myatmdd_vccdata_t *priv = vcc->dev_data;
+    int pkt_len;
+
+    DEBUG("%s\n", __FUNCTION__);
+
+    while ((skb = myatmdd_rxq_dequeue(&priv->rxqueue, &pkt_len)))
+    {
+        struct sk_buff *newskb;
+
+        /* Get a new skb to replace the one just consumed */
+        if (!(newskb = dev_alloc_skb(AAL5_BUFLEN)))
+        {
+            atomic_inc(&vcc->stats->rx_err);
+            printk(KERN_ERR KLOG_PREAMBLE "cannot receive packet - out of memory\n");
+            /* put skb back in rx queue) */
+            myatmdd_rxq_enqueue(&priv->rxqueue, skb);
+            return;
+        }
+        myatmdd_rxq_enqueue(&priv->rxqueue, newskb);
+
+        if (!atm_charge (vcc, skb->truesize))
+        {
+            /* Exceeded memory quota for this vcc
+             * NOTE: if atm_charge succeeds you must then push or accounting will screw up
+             */
+            dev_kfree_skb(skb);
+            /* &vcc->stats->drop stats incremented in atm_charge */
+        }
+        else
+        {
+            /* sk_buff passed all sanity checks! */
+            
+            /* Add received length to socket buffer */
+            skb_put(skb, pkt_len);
+        
+            /* update device stats */
+            atomic_inc(&vcc->stats->rx);
+
+            /* add timestamp for upper layers to use */
+            ktime_t kt = ktime_get_real();
+            skb->tstamp = kt;
+        
+            /* Point socket buffer at the right VCC before giving to socket layer */
+            ATM_SKB(skb)->vcc = vcc;
+        
+            /* push socket buffer up to ATM layer */
+            vcc->push(vcc, skb);
+        }
+    }
+}
+
+static void myatmdd_tx_interrupt(struct atm_vcc *vcc)
+{
+    struct sk_buff *skb;
+    myatmdd_vccdata_t *priv = vcc->dev_data;
+
+    DEBUG("%s\n", __FUNCTION__);
+
+    while ((skb = myatmdd_txq_dequeue(&priv->txqueue)))
+    {
+        // Update channel stats and free the memory
+        atomic_inc(&vcc->stats->tx);
+        myatmdd_free_tx_skb(skb);
+    }
+}
+
+/*
+#########################################################
+#
+#  Function : myatmdd_emulate_loopback_hardware
+#             
+#  Purpose  : emulate things normally done by hardware
+#             i.e. copying tx bufs to rx bufs (we're modelling
+#             a loopback system here), calling the tx done
+#             interrupt, and calling the rx done interrupt.
+#
+#  Args     : priv = data private to VCC
+#             
+#  Returns  : nowt
+#             
+#  Notes    : 
+#             
+##########################################################
+#  Edit history:
+#  Who     When    What
+#  AJZ     10Apr03 Created
+##########################################################
+*/
+static void myatmdd_emulate_loopback_hardware(struct atm_vcc *vcc)
+{
+    myatmdd_vccdata_t *priv = vcc->dev_data;
+    struct sk_buff **ptxskb;
+    struct sk_buff **prxskb;
+
+    DEBUG("%s\n", __FUNCTION__);
+
+    ptxskb = priv->txqueue.hw_ptr;
+    prxskb = priv->rxqueue.hw_ptr;
+
+    /* Send each tx buff waiting to go */
+    while (priv->txqueue.status[ptxskb - priv->txqueue.start] == TX_FULL)
+    {
+        struct sk_buff *txskb = *ptxskb;
+        struct sk_buff *rxskb = *prxskb;
+        int pkt_len = priv->txqueue.pkt_len[ptxskb - priv->txqueue.start];
+        
+        /* Is there an rx buffer? */
+        if (priv->rxqueue.status[prxskb - priv->rxqueue.start] == RX_FULL)
+        {
+            /* Yes - Is the length in range? */
+            if (pkt_len <= AAL5_BUFLEN)
+            {
+                /* Yes - do the copy */
+                memcpy(rxskb->data, txskb->data,pkt_len);
+                priv->rxqueue.pkt_len[prxskb - priv->rxqueue.start] = pkt_len;
+                
+                /* Indicate rx buffer recvd */
+                priv->rxqueue.status[prxskb - priv->rxqueue.start] = RX_RECVD;
+                
+                /* increment and maybe wrap rx pointer */
+                if (++prxskb == priv->rxqueue.end)
+                    prxskb = priv->rxqueue.start;
+                priv->rxqueue.hw_ptr = prxskb;
+            }
+            else
+            {
+                /* No - then h/w cannot do a recv */
+                printk(KERN_ERR KLOG_PREAMBLE "recvd frame too long - discarded\n");
+            }
+        }
+        else
+        {
+            /* No - then h/w cannot do a recv */
+            printk(KERN_ERR KLOG_PREAMBLE "no rx buffers available\n");
+        }
+        
+        /* Indicate tx buffer sent */
+        priv->txqueue.status[ptxskb - priv->txqueue.start] = TX_SENT;
+
+        /* increment and maybe wrap tx pointer */
+        if (++ptxskb == priv->txqueue.end)
+            ptxskb = priv->txqueue.start;
+        priv->txqueue.hw_ptr = ptxskb;
+        
+        /* Call tx ring interrupt handler */
+        myatmdd_tx_interrupt(vcc);
+           
+        /* Call tx ring interrupt handler */
+        myatmdd_rx_interrupt(vcc);
+    }
+}
+
+/*
+#########################################################
+#
+#  Function : functions for manipulating circular buffs
+#             
+#  Purpose  : 
+#             
+#  Args     : 
+#             
+#  Returns  : 
+#             
+#  Notes    : 
+#             
+##########################################################
+#  Edit history:
+#  Who     When    What
+#  AJZ     10Apr03 Created
+##########################################################
+*/
+
+static int myatmdd_init_rxq(myatmdd_rxq_t *queue, int size)
+{
+    /* TODO - cope with kmalloc failure */
+    struct sk_buff **pskb;
+    int i;
+
+    DEBUG("%s\n", __FUNCTION__);
+    queue->hw_ptr = queue->head = queue->tail = 
+        queue->start = kmalloc(size * sizeof(struct sk_buff *), GFP_KERNEL);
+    queue->end = &queue->start[size];
+    for (pskb = queue->start; pskb < queue->end; pskb++)
+        *pskb = NULL;
+
+    queue->status = kmalloc(size * sizeof(myatmdd_rxstatus_e),GFP_KERNEL);
+    for (i = 0; i < size; i++)
+        queue->status[i] = RX_EMPTY;
+
+    queue->pkt_len = kmalloc(size * sizeof(int),GFP_KERNEL);
+    for (i = 0; i < size; i++)
+        queue->pkt_len[i] = 0;
+
+    return 0;
+}
+
+static int myatmdd_init_txq(myatmdd_txq_t *queue, int size)
+{
+    /* TODO - cope with kmalloc failure */
+    struct sk_buff **pskb;
+    int i;
+
+    DEBUG("%s\n", __FUNCTION__);
+    queue->hw_ptr = queue->head = queue->tail = 
+        queue->start = kmalloc(size * sizeof(struct sk_buff *), GFP_KERNEL);
+    queue->end = &queue->start[size];
+    for (pskb = queue->start; pskb < queue->end; pskb++)
+        *pskb = NULL;
+
+    queue->status = kmalloc(size * sizeof(myatmdd_rxstatus_e),GFP_KERNEL);
+    for (i = 0; i < size; i++)
+        queue->status[i] = TX_EMPTY;
+
+    queue->pkt_len = kmalloc(size * sizeof(int),GFP_KERNEL);
+    for (i = 0; i < size; i++)
+        queue->pkt_len[i] = 0;
+
+    return 0;
+}
+
+static int myatmdd_release_rxq(myatmdd_rxq_t *queue)
+{
+    struct sk_buff **pskb;
+
+    DEBUG("%s\n", __FUNCTION__);
+    for (pskb = queue->start; pskb < queue->end; pskb++)
+    {
+        /* Is there an skb here */
+        if (*pskb == NULL)
+            continue;   /* No, so skip this entry in ring */
+
+        /* Yes - free it */
+        dev_kfree_skb(*pskb);
+    }
+    kfree(queue->start);
+    kfree(queue->status);
+    kfree(queue->pkt_len);
+
+    return 0;
+}
+
+static int myatmdd_release_txq(myatmdd_txq_t *queue)
+{
+    struct sk_buff **pskb;
+
+    DEBUG("%s\n", __FUNCTION__);
+    /* Scan through all TX bd's and cleanup */
+    for (pskb = queue->start; pskb < queue->end; pskb++)
+    {  
+        /* Is this buffer currently unused - i.e. no skb */
+        if (*pskb == NULL)
+            continue;             /* Yes, so ignore it */
+
+        /* If we reach here, we have found a socket buffer that
+         * exists in the TX ring and is waiting to be released.
+         */
+        printk(KERN_WARNING KLOG_PREAMBLE "discarding unsent tx sk_buff\n");
+        atomic_inc(&ATM_SKB(*pskb)->vcc->stats->tx_err);
+        myatmdd_free_tx_skb(*pskb);
+    }
+    kfree(queue->start);
+    kfree(queue->status);
+    kfree(queue->pkt_len);
+
+    return 0;
+}
+
+/* returns non-zero for "out of space" */
+static int myatmdd_txq_enqueue(myatmdd_txq_t *queue, struct sk_buff *skb)
+{
+    /* increment head and wrap */
+    struct sk_buff **newhead = queue->head + 1;
+    if (newhead == queue->end)
+        newhead = queue->start;
+
+    DEBUG("%s\n", __FUNCTION__);
+
+    /* abort if tx ring full */
+    if (newhead == queue->tail)
+        return -1;
+    
+    /* all is okay if we're here */
+    *queue->head = skb;
+    /* Tell hardware there's a buffer to send */
+    queue->status[queue->head - queue->start] = TX_FULL;
+    queue->pkt_len[queue->head - queue->start] = skb->len;
+    queue->head = newhead;
+    return 0;
+}
+
+/* returns non-zero for "out of space" */
+static int myatmdd_rxq_enqueue(myatmdd_rxq_t *queue, struct sk_buff *skb /* empty buffer */)
+{
+    /* increment head and wrap */
+    struct sk_buff **newhead = queue->head + 1;
+    if (newhead == queue->end)
+        newhead = queue->start;
+
+    DEBUG("%s\n", __FUNCTION__);
+
+    /* abort if rx ring full */
+    if (newhead == queue->tail)
+        return -1;
+    
+    /* all is okay if we're here */
+    *queue->head = skb;
+    /* Tell hardware there's a buffer to send */
+    queue->status[queue->head - queue->start] = RX_FULL;
+    queue->head = newhead;
+    return 0;
+}
+
+static struct sk_buff *myatmdd_txq_dequeue(myatmdd_txq_t *queue)
+{
+    DEBUG("%s\n", __FUNCTION__);
+    if (queue->tail != queue->head && queue->status[queue->tail - queue->start] == TX_SENT)
+    {
+        struct sk_buff *skb = *queue->tail;
+
+        /* increment tail and wrap */
+        struct sk_buff **newtail = queue->tail + 1;
+        if (newtail == queue->end)
+            newtail = queue->start;
+        *queue->tail = NULL;
+        queue->status[queue->tail - queue->start] = TX_EMPTY;
+        queue->tail = newtail;
+        return skb;
+    }
+    return NULL;
+}
+
+/* returns NULL for "no new recvd frames" */
+static struct sk_buff *myatmdd_rxq_dequeue(myatmdd_rxq_t *queue, int *pkt_len)
+{
+    DEBUG("%s\n", __FUNCTION__);
+    if (queue->tail != queue->head && queue->status[queue->tail - queue->start] == RX_RECVD)
+    {
+        struct sk_buff *skb = *queue->tail;
+
+        /* increment tail and wrap */
+        struct sk_buff **newtail = queue->tail + 1;
+        if (newtail == queue->end)
+            newtail = queue->start;
+        *queue->tail = NULL;
+        queue->status[queue->tail - queue->start] = RX_EMPTY;
+        *pkt_len = queue->pkt_len[queue->tail - queue->start];
+        queue->tail = newtail;
+        return skb;
+    }
+    return NULL;
+}
+
+/*
+#########################################################
+#
+#  Functions : 	Implementations of function ptrs in
+#               myatmdd_phy_ops.  This is the phy driver
+#	start:      myatmdd_phy_start,
+#	ioctl:      myatmdd_phy_ioctl,
+#	interrupt:  myatmdd_phy_int,
+#             
+#  Purpose  : See ATM device driver interface v0.1
+#             
+#  Notes    : Conforming to Linux ATM device driver i/f
+#             interface.  Draft version 0.1
+#             
+#             Designed to work with multiple devices
+##########################################################
+#  Edit history:
+#  Who     When    What
+#  AJZ     10Apr03 Created
+##########################################################
+*/
+static int myatmdd_phy_start(struct atm_dev *dev)
+{
+    /* Provide ATM driver with a pointer via which it
+     * may invoke PHY driver's IOCTL or interrupt 
+     * handlers.
+     */
+    dev->phy = &myatmdd_phy_ops;
+
+    /* If required allocate phy private data and save
+     * pointer in dev->phy_data;
+     */
+    
+    /* TODO Initialise PHY hardware... */
+
+    return 0;
+}
+
+/* Should be called by SAR driver when it needs to handle an interrupt
+ * triggered by PHY.
+ */
+static void myatmdd_phy_int(struct atm_dev *dev)
+{
+    /* Handle interrupt triggered by PHY */
+}
+
+/* Gets called by SAR driver IOCTL handler for IOCTLS it doesn't recognise */
+static int myatmdd_phy_ioctl(struct atm_dev *dev,unsigned int cmd,void *arg)
+{
+	switch (cmd)
+    {
+//		case SONET_GETSTATZ:
+        default:
+            return -EINVAL;
+    }
+}
+
+/*
+#########################################################
+#
+#  Function : myatmdd_free_tx_skb
+#             
+#  Purpose  : frees an sk_buff.
+#             
+#  Args     : skb=pointer to socket buffer
+#             
+#  Notes    : Tries to use the upper layer pop() function
+#             but uses dev_kfree_skb() if this doesn't exist
+##########################################################
+#  Edit history:
+#  Who     When    What
+#  AJZ     10Apr03 Created
+##########################################################
+*/
+static void myatmdd_free_tx_skb(struct sk_buff *skb)
+{  
+    struct atm_vcc *vcc;
+
+    DEBUG("%s\n", __FUNCTION__);
+
+    /* See if we can use the VCC pop function */
+    if (((vcc = ATM_SKB(skb)->vcc) != NULL) && (vcc->pop != NULL))
+    {
+        /* Yes, so use ATM socket layer pop function */
+        vcc->pop(vcc, skb);
+    }
+    else
+    {  
+        printk(KERN_WARNING KLOG_PREAMBLE "unable to call skb free function\n");
+        /* No, so free socket buffer */
+        dev_kfree_skb(skb);
+    }
+}
+
+/*
+#########################################################
+#
+#  Functions : 	Implementations of function ptrs in
+#               myatmdd_ops.
+#   myatmdd_open(),
+#	myatmdd_close(),
+#	myatmdd_ioctl(),
+
+
+#	myatmdd_send(),
+#	myatmdd_sg_send(),
+#	myatmdd_change_qos(),
+#	myatmdd_proc_read()
+# 
+#             
+#  Purpose  : See ATM device driver interface v0.1
+#             
+#  Notes    : Conforming to Linux ATM device driver i/f
+#             interface.  Draft version 0.1
+#             
+#             Designed to work with multiple devices
+##########################################################
+#  Edit history:
+#  Who     When    What
+#  AJZ     10Apr03 Created
+##########################################################
+*/
+static int myatmdd_open(struct atm_vcc *vcc)
+{
+    myatmdd_vccdata_t *priv;
+    int i;
+
+    DEBUG("%s\n", __FUNCTION__);
+
+    /* Make sure we are opening a AAL0 or AAL5 connection */
+    if ((vcc->qos.aal != ATM_AAL5) && (vcc->qos.aal != ATM_AAL0))
+    {
+        printk(KERN_WARNING KLOG_PREAMBLE "invalid AAL\n");
+        return -EINVAL;
+    }
+
+    /* Address is in use */
+    set_bit(ATM_VF_ADDR, &vcc->flags);
+
+    /* Allocate some vcc-private memory */
+    vcc->dev_data = kmalloc(sizeof(myatmdd_vccdata_t), GFP_KERNEL);
+    if (vcc->dev_data == NULL)
+        return -ENOMEM;
+    priv = vcc->dev_data;
+
+    /* Setup the hardware for new VC... */
+
+    /* Do not allow half open VCs - otherwise the example driver will not be able
+     * to loop back frames sent !
+     */
+    if (vcc->qos.rxtp.traffic_class == ATM_NONE || vcc->qos.txtp.traffic_class == ATM_NONE)
+    {
+        kfree(vcc->dev_data);
+        return -EPERM;
+    }
+
+    /* Create rx/tx queues for this VC */
+    myatmdd_init_txq(&priv->txqueue, TXQ_SZ);
+    myatmdd_init_rxq(&priv->rxqueue, RXQ_SZ);
+    
+    /* Fill rx queue with empty skbuffs */
+    for (i = 0 ; i < RXQ_SZ - 1; i++)
+    {
+        struct sk_buff *skb = dev_alloc_skb(AAL5_BUFLEN);
+        myatmdd_rxq_enqueue(&priv->rxqueue,skb);
+    }
+   
+    /* Connection is now ready to receive data */
+    set_bit(ATM_VF_READY, &vcc->flags);
+
+    return 0;
+}
+
+static void myatmdd_close(struct atm_vcc *vcc)
+{
+    myatmdd_vccdata_t *priv = vcc->dev_data;
+
+    DEBUG("%s\n", __FUNCTION__);
+
+    /* Indicate channel closed */
+    clear_bit(ATM_VF_READY, &vcc->flags);
+
+    /* TODO Uninitialise the hardware for this VC... */
+    
+    /* empty the rx and tx queues */
+    myatmdd_release_txq(&priv->txqueue);
+    myatmdd_release_rxq(&priv->rxqueue);
+
+    /* Free the vcc-private memory */
+    kfree(vcc->dev_data);
+}
+  
+static int myatmdd_ioctl(struct atm_dev *dev, unsigned int cmd,void *arg)
+{
+    /* myatmdd does not currently have an ioctl interface so pass ioctl onto PHY */
+    if (dev->phy && dev->phy->ioctl) {
+        return dev->phy->ioctl(dev, cmd, arg);
+    }
+    return -EINVAL;
+}
+
+
+
+
+
+
+
+
+
+
+
+/* Note may be called in either process or interrupt context! */
+static int myatmdd_send(struct atm_vcc *vcc,struct sk_buff *skb)
+{
+    myatmdd_vccdata_t *priv = vcc->dev_data;
+
+    DEBUG("%s\n", __FUNCTION__);
+
+    /* Assign VCC to socket buffer
+     * Note: this must be done before attempting to call
+     * myatmdd_free_tx_skb() as this may use ATM_SKB(skb)->vcc->pop()
+     */
+    ATM_SKB(skb)->vcc = vcc;
+
+    /* Setup hardware to send and arrange callback of myatmdd_send_complete... */
+
+    /* In this example ATM device driver all VCs are looped back.
+     * So copy to the rxq and emulate an rx interrupt
+     */
+
+    /* Can we accept another skb to send ? */
+    if (myatmdd_txq_enqueue(&priv->txqueue, skb))
+    {
+        /* No - free socket buffer */
+        myatmdd_free_tx_skb(skb);
+        
+        /* Update tx channel stats */
+        atomic_inc(&vcc->stats->tx_err);
+        
+        /* Tell protocol layer to back off */
+        return(-EBUSY);
+    }
+
+    /* This is the bit which copies the tx ring to the rx ring,
+     * and triggers emulated rx and tx interrupts
+     */
+    myatmdd_emulate_loopback_hardware(vcc);
+    
+    return 0;
+}
+
+static int myatmdd_change_qos(struct atm_vcc *vcc,struct atm_qos *qos,int flgs)
+{
+    return 0;
+}
+
+static int myatmdd_proc_read(struct atm_dev *dev,loff_t *pos,char *page)
+{
+    int left = (int) *pos;
+    
+    if (!left--)
+        return sprintf(page, "1st line of stats\n");
+    if (!left--)
+        return sprintf(page, "2nd line of stats\n");
+    if (!left--)
+        return sprintf(page, "3rd line of stats\n");
+
+    return 0;
+}
+
+/*
+#########################################################
+#
+#  Function : myatmdd_init
+#             
+#  Purpose  : init the module, init and register the ATM device
+#             
+#  Args     : none
+#             
+#  Returns  : return code
+#             
+#  Notes    : 
+#             
+##########################################################
+#  Edit history:
+#  Who     When    What
+#  AJZ     10Apr03 Created
+##########################################################
+*/
+int __init myatmdd_init(void)
+{
+    myatmdd_devdata_t *priv = kmalloc(sizeof(myatmdd_devdata_t),GFP_KERNEL);
+
+    if (priv == NULL)
+        return -ENOMEM;
+
+    /* Register the new device */
+    myatmdd_dev = atm_dev_register(MYATMDD,NULL,&myatmdd_ops,-1,NULL);
+    
+    /* Were we able to register this device? */
+    if (myatmdd_dev == NULL)
+    {
+        printk(KERN_ERR KLOG_PREAMBLE "failed to register CPM ATM device\n");
+        return -EPERM;
+    }
+
+    /* Save pointer to device private data */
+    myatmdd_dev->dev_data = priv;
+
+    /* Initialise device parameters */
+    myatmdd_dev->ci_range.vpi_bits = MYATMDD_VPI_BITS;
+    myatmdd_dev->ci_range.vci_bits = MYATMDD_VCI_BITS;
+    myatmdd_dev->link_rate = MYATMDD_PCR;
+    
+    /* Set up phy device */
+    myatmdd_phy_start(myatmdd_dev);
+    
+    /* TODO Initialise SAR hardware... */
+
+    /* Console output */
+    printk(KERN_INFO KLOG_PREAMBLE "Initialised\n");
+
+    return 0;
+}
+
+/* NOTE:
+ * module_init() is called by insmod, if built as module, 
+ * or by do_initcalls(), if built as a resident driver.
+ */
+module_init(myatmdd_init);
+
+/*
+#########################################################
+#
+#  Function : myatmdd_exit
+#             
+#  Purpose  : delete module, uninit and dereg ATM device
+#             
+#  Args     : none
+#             
+#  Returns  : none
+#             
+#  Notes    : 
+#             
+##########################################################
+#  Edit history:
+#  Who     When    What
+#  AJZ     10Apr03 Created
+##########################################################
+*/
+
+#ifdef MODULE
+static void __exit myatmdd_exit(void)
+{
+    /* Disable SAR hardware... */
+
+    /* Console output */
+    printk(KERN_ERR KLOG_PREAMBLE "Uninitialised\n");
+    kfree(myatmdd_dev->dev_data);
+    atm_dev_deregister(myatmdd_dev);
+}
+module_exit(myatmdd_exit);
+
+#endif /* MODULE */
diff -urN linux-5.9/drivers.org/atm/Kconfig linux-5.9/drivers/atm/Kconfig
--- linux-5.9/drivers.org/atm/Kconfig	2020-10-11 23:15:50.000000000 +0200
+++ linux-5.9/drivers/atm/Kconfig	2020-11-03 13:31:48.120071319 +0100
@@ -15,6 +15,14 @@
 
 if ATM_DRIVERS && NETDEVICES && ATM
 
+config ATM_DD
+	tristate "ATM loopback"
+	depends on INET && ATM
+	help
+	  This is an example atm driver.  It does not require any actual ATM
+	  hardware.  It supports AAL5 and AAL0.  Frames are merely looped back
+	  to the sender on the same VC they were sent.
+
 config ATM_SOLOS
 	tristate "Solos ADSL2+ PCI Multiport card driver"
 	depends on PCI
--- linux-7.1/drivers/atm/Makefile.orig	2026-06-14 16:58:38.000000000 +0200
+++ linux-7.1/drivers/atm/Makefile	2026-06-19 12:13:50.344836302 +0200
@@ -1,3 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0
 
+obj-$(CONFIG_ATM_DD)		+= atmdd.o
 obj-$(CONFIG_ATM_SOLOS)		+= solos-pci.o