drm/panel-edp: Allow querying the detected panel via debugfs

Recently we added generic "edp-panel"s probed by EDID. To support
panels in this way we look at the panel ID in the EDID and look up the
panel in a table that has power sequence timings. If we find a panel
that's not in the table we will still attempt to use it but we'll use
conservative timings. While it's likely that these conservative
timings will work for most nearly all panels, the performance of
turning the panel off and on suffers.

We'd like to be able to reliably detect the case that we're using the
hardcoded timings without relying on parsing dmesg. This allows us to
implement tests that ensure that no devices get shipped that are
relying on the conservative timings.

Let's add a new debugfs entry to panel devices. It will have one of:
* UNKNOWN - We tried to detect a panel but it wasn't in our table.
* HARDCODED - We're not using generic "edp-panel" probed by EDID.
* A panel name - This is the name of the panel from our table.
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220204161245.v2.3.I209d72bcc571e1d7d6b793db71bf15c9c0fc9292@changeid

drivers/gpu/drm/panel/panel-edp.c

@@ -21,6 +21,7 @@
  * DEALINGS IN THE SOFTWARE.
  */
 
+#include <linux/debugfs.h>
 #include <linux/delay.h>
 #include <linux/gpio/consumer.h>
 #include <linux/iopoll.h>
@@ -222,6 +223,8 @@ struct panel_edp {
 	struct gpio_desc *enable_gpio;
 	struct gpio_desc *hpd_gpio;
 
+	const struct edp_panel_entry *detected_panel;
+
 	struct edid *edid;
 
 	struct drm_display_mode override_mode;
@@ -606,6 +609,28 @@ static int panel_edp_get_timings(struct drm_panel *panel,
 	return p->desc->num_timings;
 }
 
+static int detected_panel_show(struct seq_file *s, void *data)
+{
+	struct drm_panel *panel = s->private;
+	struct panel_edp *p = to_panel_edp(panel);
+
+	if (IS_ERR(p->detected_panel))
+		seq_puts(s, "UNKNOWN\n");
+	else if (!p->detected_panel)
+		seq_puts(s, "HARDCODED\n");
+	else
+		seq_printf(s, "%s\n", p->detected_panel->name);
+
+	return 0;
+}
+
+DEFINE_SHOW_ATTRIBUTE(detected_panel);
+
+static void panel_edp_debugfs_init(struct drm_panel *panel, struct dentry *root)
+{
+	debugfs_create_file("detected_panel", 0600, root, panel, &detected_panel_fops);
+}
+
 static const struct drm_panel_funcs panel_edp_funcs = {
 	.disable = panel_edp_disable,
 	.unprepare = panel_edp_unprepare,
@@ -613,6 +638,7 @@ static const struct drm_panel_funcs panel_edp_funcs = {
 	.enable = panel_edp_enable,
 	.get_modes = panel_edp_get_modes,
 	.get_timings = panel_edp_get_timings,
+	.debugfs_init = panel_edp_debugfs_init,
 };
 
 #define PANEL_EDP_BOUNDS_CHECK(to_check, bounds, field) \
@@ -666,7 +692,6 @@ static const struct edp_panel_entry *find_edp_panel(u32 panel_id);
 
 static int generic_edp_panel_probe(struct device *dev, struct panel_edp *panel)
 {
-	const struct edp_panel_entry *edp_panel;
 	struct panel_desc *desc;
 	u32 panel_id;
 	char vend[4];
@@ -705,14 +730,14 @@ static int generic_edp_panel_probe(struct device *dev, struct panel_edp *panel)
 	}
 	drm_edid_decode_panel_id(panel_id, vend, &product_id);
 
-	edp_panel = find_edp_panel(panel_id);
+	panel->detected_panel = find_edp_panel(panel_id);
 
 	/*
 	 * We're using non-optimized timings and want it really obvious that
 	 * someone needs to add an entry to the table, so we'll do a WARN_ON
 	 * splat.
 	 */
-	if (WARN_ON(!edp_panel)) {
+	if (WARN_ON(!panel->detected_panel)) {
 		dev_warn(dev,
 			 "Unknown panel %s %#06x, using conservative timings\n",
 			 vend, product_id);
@@ -734,12 +759,14 @@ static int generic_edp_panel_probe(struct device *dev, struct panel_edp *panel)
 		 */
 		desc->delay.unprepare = 2000;
 		desc->delay.enable = 200;
+
+		panel->detected_panel = ERR_PTR(-EINVAL);
 	} else {
 		dev_info(dev, "Detected %s %s (%#06x)\n",
-			 vend, edp_panel->name, product_id);
+			 vend, panel->detected_panel->name, product_id);
 
 		/* Update the delay; everything else comes from EDID */
-		desc->delay = *edp_panel->delay;
+		desc->delay = *panel->detected_panel->delay;
 	}
 
 	ret = 0;