drm/i915: add i915 specific connector debugfs file for DPCD

Occasionally it would be interesting to read some of the DPCD registers
for debug purposes, without having to resort to logging. Add an i915
specific i915_dpcd debugfs file for DP and eDP connectors to dump parts
of the DPCD. Currently the DPCD addresses to be dumped are statically
configured, and more can be added trivially.

The implementation also makes it relatively easy to add other i915 and
connector specific debugfs files in the future, as necessary.

This is currently i915 specific just because there's no generic way to
do AUX transactions given just a drm_connector. However it's all pretty
straightforward to port to other drivers.

v2: Add more DPCD registers to dump.
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Bob Paauwe <bob.j.paauwe@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -4793,3 +4793,99 @@ void i915_debugfs_cleanup(struct drm_minor *minor)
 		drm_debugfs_remove_files(info_list, 1, minor);
 	}
 }
+
+struct dpcd_block {
+	/* DPCD dump start address. */
+	unsigned int offset;
+	/* DPCD dump end address, inclusive. If unset, .size will be used. */
+	unsigned int end;
+	/* DPCD dump size. Used if .end is unset. If unset, defaults to 1. */
+	size_t size;
+	/* Only valid for eDP. */
+	bool edp;
+};
+
+static const struct dpcd_block i915_dpcd_debug[] = {
+	{ .offset = DP_DPCD_REV, .size = DP_RECEIVER_CAP_SIZE },
+	{ .offset = DP_PSR_SUPPORT, .end = DP_PSR_CAPS },
+	{ .offset = DP_DOWNSTREAM_PORT_0, .size = 16 },
+	{ .offset = DP_LINK_BW_SET, .end = DP_EDP_CONFIGURATION_SET },
+	{ .offset = DP_SINK_COUNT, .end = DP_ADJUST_REQUEST_LANE2_3 },
+	{ .offset = DP_SET_POWER },
+	{ .offset = DP_EDP_DPCD_REV },
+	{ .offset = DP_EDP_GENERAL_CAP_1, .end = DP_EDP_GENERAL_CAP_3 },
+	{ .offset = DP_EDP_DISPLAY_CONTROL_REGISTER, .end = DP_EDP_BACKLIGHT_FREQ_CAP_MAX_LSB },
+	{ .offset = DP_EDP_DBC_MINIMUM_BRIGHTNESS_SET, .end = DP_EDP_DBC_MAXIMUM_BRIGHTNESS_SET },
+};
+
+static int i915_dpcd_show(struct seq_file *m, void *data)
+{
+	struct drm_connector *connector = m->private;
+	struct intel_dp *intel_dp =
+		enc_to_intel_dp(&intel_attached_encoder(connector)->base);
+	uint8_t buf[16];
+	ssize_t err;
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(i915_dpcd_debug); i++) {
+		const struct dpcd_block *b = &i915_dpcd_debug[i];
+		size_t size = b->end ? b->end - b->offset + 1 : (b->size ?: 1);
+
+		if (b->edp &&
+		    connector->connector_type != DRM_MODE_CONNECTOR_eDP)
+			continue;
+
+		/* low tech for now */
+		if (WARN_ON(size > sizeof(buf)))
+			continue;
+
+		err = drm_dp_dpcd_read(&intel_dp->aux, b->offset, buf, size);
+		if (err <= 0) {
+			DRM_ERROR("dpcd read (%zu bytes at %u) failed (%zd)\n",
+				  size, b->offset, err);
+			continue;
+		}
+
+		seq_printf(m, "%04x: %*ph\n", b->offset, (int) size, buf);
+	};
+
+	return 0;
+}
+
+static int i915_dpcd_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, i915_dpcd_show, inode->i_private);
+}
+
+static const struct file_operations i915_dpcd_fops = {
+	.owner = THIS_MODULE,
+	.open = i915_dpcd_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = single_release,
+};
+
+/**
+ * i915_debugfs_connector_add - add i915 specific connector debugfs files
+ * @connector: pointer to a registered drm_connector
+ *
+ * Cleanup will be done by drm_connector_unregister() through a call to
+ * drm_debugfs_connector_remove().
+ *
+ * Returns 0 on success, negative error codes on error.
+ */
+int i915_debugfs_connector_add(struct drm_connector *connector)
+{
+	struct dentry *root = connector->debugfs_entry;
+
+	/* The connector must have been registered beforehands. */
+	if (!root)
+		return -ENODEV;
+
+	if (connector->connector_type == DRM_MODE_CONNECTOR_DisplayPort ||
+	    connector->connector_type == DRM_MODE_CONNECTOR_eDP)
+		debugfs_create_file("i915_dpcd", S_IRUGO, root, connector,
+				    &i915_dpcd_fops);
+
+	return 0;
+}

drivers/gpu/drm/i915/i915_drv.h

@@ -3007,6 +3007,7 @@ int i915_verify_lists(struct drm_device *dev);
 /* i915_debugfs.c */
 int i915_debugfs_init(struct drm_minor *minor);
 void i915_debugfs_cleanup(struct drm_minor *minor);
+int i915_debugfs_connector_add(struct drm_connector *connector);
 #ifdef CONFIG_DEBUG_FS
 void intel_display_crc_init(struct drm_device *dev);
 #else

drivers/gpu/drm/i915/intel_dp.c

@@ -5584,6 +5584,8 @@ intel_dp_init_connector(struct intel_digital_port *intel_dig_port,
 		I915_WRITE(PEG_BAND_GAP_DATA, (temp & ~0xf) | 0xd);
 	}
 
+	i915_debugfs_connector_add(connector);
+
 	return true;
 }