Re: [v8 1/6] drm/panel: add basic DP AUX backlight support

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Hi

Am 12.07.21 um 11:41 schrieb Thomas Zimmermann:


Am 26.06.21 um 18:51 schrieb Rajeev Nandan:
Some panels support backlight control over DP AUX channel using
VESA's standard backlight control interface.
Using new DRM eDP backlight helpers, add support to create and
register a backlight for those panels in drm_panel to simplify
the panel drivers.

The panel driver with access to "struct drm_dp_aux" can create and
register a backlight device using following code snippet in its
probe() function:

    err = drm_panel_dp_aux_backlight(panel, aux);
    if (err)
        return err;

Then drm_panel will handle backlight_(enable|disable) calls
similar to the case when drm_panel_of_backlight() is used.

Currently, we are not supporting one feature where the source
device can combine the backlight brightness levels set through
DP AUX and the BL_PWM_DIM eDP connector pin. Since it's not
required for the basic backlight controls, it can be added later.

Signed-off-by: Rajeev Nandan <rajeevny@xxxxxxxxxxxxxx>
Reviewed-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
Reviewed-by: Lyude Paul <lyude@xxxxxxxxxx>
---

Changes in v5:
- New

Changes in v6:
- Fixed ordering of memory allocation (Douglas)
- Updated word wrapping in a comment (Douglas)

Changes in v8:
- Now using backlight_is_blank() to get the backlight blank status (Sam Ravnborg)

  drivers/gpu/drm/drm_panel.c | 108 ++++++++++++++++++++++++++++++++++++++++++++
  include/drm/drm_panel.h     |  15 ++++--
  2 files changed, 119 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
index f634371..4fa1e3b 100644
--- a/drivers/gpu/drm/drm_panel.c
+++ b/drivers/gpu/drm/drm_panel.c
@@ -26,12 +26,20 @@
  #include <linux/module.h>
  #include <drm/drm_crtc.h>
+#include <drm/drm_dp_helper.h>
  #include <drm/drm_panel.h>
  #include <drm/drm_print.h>
  static DEFINE_MUTEX(panel_lock);
  static LIST_HEAD(panel_list);
+struct dp_aux_backlight {
+    struct backlight_device *base;
+    struct drm_dp_aux *aux;
+    struct drm_edp_backlight_info info;
+    bool enabled;
+};
+
  /**
   * DOC: drm panel
   *
@@ -342,6 +350,106 @@ int drm_panel_of_backlight(struct drm_panel *panel)
      return 0;
  }
  EXPORT_SYMBOL(drm_panel_of_backlight);
+
+static int dp_aux_backlight_update_status(struct backlight_device *bd)
+{
+    struct dp_aux_backlight *bl = bl_get_data(bd);
+    u16 brightness = backlight_get_brightness(bd);
+    int ret = 0;
+
+    if (!backlight_is_blank(bd)) {
+        if (!bl->enabled) {
+            drm_edp_backlight_enable(bl->aux, &bl->info, brightness);
+            bl->enabled = true;
+            return 0;
+        }
+        ret = drm_edp_backlight_set_level(bl->aux, &bl->info, brightness);
+    } else {
+        if (bl->enabled) {
+            drm_edp_backlight_disable(bl->aux, &bl->info);
+            bl->enabled = false;
+        }
+    }
+
+    return ret;
+}
+
+static const struct backlight_ops dp_aux_bl_ops = {
+    .update_status = dp_aux_backlight_update_status,
+};
+
+/**
+ * drm_panel_dp_aux_backlight - create and use DP AUX backlight
+ * @panel: DRM panel
+ * @aux: The DP AUX channel to use
+ *
+ * Use this function to create and handle backlight if your panel
+ * supports backlight control over DP AUX channel using DPCD
+ * registers as per VESA's standard backlight control interface.
+ *
+ * When the panel is enabled backlight will be enabled after a
+ * successful call to &drm_panel_funcs.enable()
+ *
+ * When the panel is disabled backlight will be disabled before the
+ * call to &drm_panel_funcs.disable().
+ *
+ * A typical implementation for a panel driver supporting backlight
+ * control over DP AUX will call this function at probe time.
+ * Backlight will then be handled transparently without requiring
+ * any intervention from the driver.
+ *
+ * drm_panel_dp_aux_backlight() must be called after the call to drm_panel_init().
+ *
+ * Return: 0 on success or a negative error code on failure.
+ */
+int drm_panel_dp_aux_backlight(struct drm_panel *panel, struct drm_dp_aux *aux)
+{
+    struct dp_aux_backlight *bl;
+    struct backlight_properties props = { 0 };
+    u16 current_level;
+    u8 current_mode;
+    u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE];
+    int ret;
+
+    if (!panel || !panel->dev || !aux)
+        return -EINVAL;
+
+    ret = drm_dp_dpcd_read(aux, DP_EDP_DPCD_REV, edp_dpcd,
+                   EDP_DISPLAY_CTL_CAP_SIZE);

This creates a cyclic dependency between drm_kms_helper-ko and drm.ko. drm_panel.c is in the latter, while drm_dp_dpcd_read() in drm_dp_helper.c is in the former. Please fix.

FYI, build DRM as modules and the error shows up during make module_install.

Best regards
Thomas


--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

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