[PATCH 1/1] drm/dp: Add debufs support for DP dpcd log

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Patch adds support for debugging DisplayPort :

* All dpcd read/write transactions are logged
* Logging done per AUX interface
* Use following command to to list AUX transactions:

bash # cat /sys/kernel/debug/drm_dp_aux/$AUXNAME
@0x0000: 0x12
@0x0001: 0x14
@0x0002: 0xc4
@0x0003: 0x01
@0x0004: 0x01
@0x0005: 0x01
@0x0006: 0x01
@0x0007: 0x81
@0x0008: 0x02
@0x0009: 0x02
@0x000a: 0x06
@0x000b: 0x00
@0x000c: 0x00
@0x000d: 0x00
@0x000e: 0x00
@0x0100: 0x14
@0x0101: 0x82
@0x0102: 0x00
@0x0103: 0x0a
@0x0104: 0x0a
@0x0107: 0x10
@0x0108: 0x01
@0x0202: 0x77
@0x0203: 0x00
@0x0204: 0x01
@0x0205: 0x02
@0x0206: 0x66
@0x0207: 0x00

Above information will help to debug DisplayPort related runtime issues
knowing what communication was done between DisplayPort sink and source.

Signed-off-by: Tejas Upadhyay <tejas.upadhyay@xxxxxxxxxx>
Signed-off-by: Hyun Kwon <hyun.kwon@xxxxxxxxxx>
---
 drivers/gpu/drm/Kconfig         |  10 +++
 drivers/gpu/drm/drm_dp_helper.c | 174 +++++++++++++++++++++++++++++++++++++++-
 include/drm/drm_dp_helper.h     |   7 ++
 3 files changed, 190 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index f3c71e3..bb16e24 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -34,6 +34,16 @@ config DRM_DP_AUX_CHARDEV
          read and write values to arbitrary DPCD registers on the DP aux
          channel.

+config DRM_DEBUG_DP
+       bool "DRM dp debug helper"
+       default n
+       depends on DRM
+       help
+         Choose this option to enable a debugfs functionality for drm-dp.
+         Will help in debugging display port related issue.
+         Recommended for driver developer as well as tester.
+         Say "Y" to enable debug support.
+
 config DRM_DEBUG_MM
        bool "Insert extra checks and debug info into the DRM range managers"
        default n
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 08af8d6..e8be361 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -28,6 +28,9 @@
 #include <linux/sched.h>
 #include <linux/i2c.h>
 #include <linux/seq_file.h>
+#ifdef CONFIG_DRM_DEBUG_DP
+#include <linux/debugfs.h>
+#endif
 #include <drm/drm_dp_helper.h>
 #include <drm/drmP.h>

@@ -57,6 +60,171 @@ static u8 dp_get_lane_status(const u8 link_status[DP_LINK_STATUS_SIZE],
        return (l >> s) & 0xf;
 }

+#ifdef CONFIG_DRM_DEBUG_DP
+
+static uint drm_dp_debugfs_dpcd_size = 0x5ff;
+module_param_named(debugfs_dpcd_size, drm_dp_debugfs_dpcd_size, uint, 0444);
+MODULE_PARM_DESC(debugfs_dpcd_size, "Debugfs DPCD buffer size (default: 1544)");
+
+static struct dentry *root;
+
+static bool drm_dp_debugfs_bitmap_is_set(struct drm_dp_aux *aux,
+                                        unsigned int pos)
+{
+       u8 byte, bit;
+
+       byte = pos / 8;
+       bit = pos % 8;
+
+       return !!(aux->dpcd_bitmap[byte] & BIT(bit));
+}
+
+static void drm_dp_debugfs_bitmap_set(struct drm_dp_aux *aux, unsigned int pos)
+{
+       u8 byte, bit;
+
+       byte = pos / 8;
+       bit = pos % 8;
+       aux->dpcd_bitmap[byte] |= BIT(bit);
+}
+
+/* DP debugfs read API, to be called by user app */
+static ssize_t drm_dp_debugfs_read(struct file *f, char __user *buf,
+                                  size_t size, loff_t *pos)
+{
+       struct drm_dp_aux *aux = (struct drm_dp_aux *)f->f_inode->i_private;
+       char *kern_buff = NULL;
+       unsigned int i;
+       size_t kern_buff_len;
+       int err;
+
+       if (size <= 0)
+               return -EINVAL;
+       if (*pos != 0)
+               return 0;
+
+       kern_buff_len = size;
+       kern_buff = kzalloc(kern_buff_len, GFP_KERNEL);
+       if (!kern_buff)
+               return -ENOMEM;
+
+       for (i = 0; i < drm_dp_debugfs_dpcd_size; i++) {
+               if (drm_dp_debugfs_bitmap_is_set(aux, i)) {
+                       char str[16] = "";
+
+                       sprintf(str, "@0x%04x: 0x%02x\n", i, aux->dpcd_data[i]);
+                       if (kern_buff_len < strlen(str))
+                               break;
+
+                       strcat(kern_buff, str);
+                       kern_buff_len -= strlen(str);
+               }
+       }
+       kern_buff_len = strlen(kern_buff);
+       size = min(size, kern_buff_len);
+       err = copy_to_user(buf, kern_buff, size);
+       kfree(kern_buff);
+       if (err)
+               return err;
+       *pos = size + 1;
+
+       return size;
+}
+
+static const struct file_operations fops_drm_dp_dbgfs = {
+       .owner = THIS_MODULE,
+       .read = drm_dp_debugfs_read,
+};
+
+static int drm_dp_debugfs_init(struct drm_dp_aux *aux)
+{
+       struct dentry *entry;
+       u8 *bitmap, *data;
+       int err;
+
+       /* FIXME: better be under drm debugfs dir, and cleaned up properly */
+       if (!root) {
+               root = debugfs_create_dir("drm_dp_aux", NULL);
+               if (!root) {
+                       DRM_ERROR("debugfs_create_dir failed for root\n");
+                       return -ENODEV;
+               }
+       }
+
+       /* FIXME: There may be a better name than the aux name */
+       entry = debugfs_create_file(aux->name, 0444, root, aux,
+                                   &fops_drm_dp_dbgfs);
+       if (!entry) {
+               DRM_ERROR("debugfs_create_file testcase failed\n");
+               err = -ENODEV;
+               goto err_dbgfs;
+       }
+
+       bitmap = devm_kzalloc(aux->dev,
+                             sizeof(*bitmap) * (drm_dp_debugfs_dpcd_size / 8),
+                             GFP_KERNEL);
+       if (unlikely(!bitmap)) {
+               err = -ENOMEM;
+               goto err_dbgfs;
+       }
+
+       data = devm_kzalloc(aux->dev, sizeof(*data) * drm_dp_debugfs_dpcd_size,
+                           GFP_KERNEL);
+       if (unlikely(!data)) {
+               err = -ENOMEM;
+               goto err_dbgfs;
+       }
+
+       aux->dpcd_data = data;
+       aux->dpcd_bitmap = bitmap;
+
+       return 0;
+
+err_dbgfs:
+       debugfs_remove_recursive(entry);
+       return err;
+}
+
+/* Deinit DP debugfs */
+static void drm_dp_debugfs_deinit(struct drm_dp_aux *aux)
+{
+       struct dentry *entry;
+
+       entry = debugfs_lookup(aux->name, root);
+       debugfs_remove_recursive(entry);
+}
+
+static void drm_dp_debugfs_log(struct drm_dp_aux *aux,
+                              struct drm_dp_aux_msg *msg)
+{
+       u8 *buf;
+       unsigned int i;
+
+       buf = (u8 *)msg->buffer;
+       for (i = 0; i < msg->size; i++) {
+               aux->dpcd_data[msg->address + i] = buf[i];
+               drm_dp_debugfs_bitmap_set(aux, msg->address + i);
+       }
+}
+
+#else
+
+static void drm_dp_debugfs_log(struct drm_dp_aux *aux,
+                              struct drm_dp_aux_msg *msg)
+{
+}
+
+static int drm_dp_debugfs_init(struct drm_dp_aux *aux)
+{
+       return 0;
+}
+
+static void drm_dp_debugfs_deinit(struct drm_dp_aux *aux)
+{
+}
+
+#endif
+
 bool drm_dp_channel_eq_ok(const u8 link_status[DP_LINK_STATUS_SIZE],
                          int lane_count)
 {
@@ -229,6 +397,8 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
        ret = err;

 unlock:
+       /* Log dpcd aux write transactions*/
+       drm_dp_debugfs_log(aux, &msg);
        mutex_unlock(&aux->hw_mutex);
        return ret;
 }
@@ -1108,7 +1278,8 @@ int drm_dp_aux_register(struct drm_dp_aux *aux)
                drm_dp_aux_unregister_devnode(aux);
                return ret;
        }
-
+       /* Init DP debufs*/
+       drm_dp_debugfs_init(aux);
        return 0;
 }
 EXPORT_SYMBOL(drm_dp_aux_register);
@@ -1119,6 +1290,7 @@ EXPORT_SYMBOL(drm_dp_aux_register);
  */
 void drm_dp_aux_unregister(struct drm_dp_aux *aux)
 {
+       drm_dp_debugfs_deinit(aux);
        drm_dp_aux_unregister_devnode(aux);
        i2c_del_adapter(&aux->ddc);
 }
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index b17476a..442dfb8 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -962,6 +962,8 @@ struct drm_dp_aux_msg {
  * @crc_work: worker that captures CRCs for each frame
  * @crc_count: counter of captured frame CRCs
  * @transfer: transfers a message representing a single AUX transaction
+ * @dpcd_data: store aux transactions for dp debugfs
+ * @dpcd_bitmap: store a bitmap for valid dpcd data
  *
  * The .dev field should be set to a pointer to the device that implements
  * the AUX channel.
@@ -1010,6 +1012,11 @@ struct drm_dp_aux {
         * @i2c_defer_count: Counts I2C DEFERs, used for DP validation.
         */
        unsigned i2c_defer_count;
+#ifdef CONFIG_DRM_DEBUG_DP
+       /* aux transactions for dp debugfs*/
+       u8 *dpcd_data;
+       u8 *dpcd_bitmap;
+#endif
 };

 ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset,
--
2.7.4

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