[v7 1/5] drm/panel: add basic DP AUX backlight support

Rajeev Nandan
2021-06-19T10:41:30Z

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@codeaurora.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Lyude Paul <lyude@redhat.com>
---

(no changes since v6)

Changes in v5:
- New

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

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..9e65342 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 (brightness > 0) {
+ 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);
+ if (ret < 0)
+ return ret;
+
+ if (!drm_edp_backlight_supported(edp_dpcd)) {
+ DRM_DEV_INFO(panel->dev, "DP AUX backlight is not supported\n");
+ return 0;
+ }
+
+ bl = devm_kzalloc(panel->dev, sizeof(*bl), GFP_KERNEL);
+ if (!bl)
+ return -ENOMEM;
+
+ bl->aux = aux;
+
+ ret = drm_edp_backlight_init(aux, &bl->info, 0, edp_dpcd,
+ &current_level, &current_mode);
+ if (ret < 0)
+ return ret;
+
+ props.type = BACKLIGHT_RAW;
+ props.brightness = current_level;
+ props.max_brightness = bl->info.max;
+
+ bl->base = devm_backlight_device_register(panel->dev, "dp_aux_backlight",
+ panel->dev, bl,
+ &dp_aux_bl_ops, &props);
+ if (IS_ERR(bl->base))
+ return PTR_ERR(bl->base);
+
+ panel->backlight = bl->base;
+
+ return 0;
+}
+EXPORT_SYMBOL(drm_panel_dp_aux_backlight);
#endif

MODULE_AUTHOR("Thierry Reding <treding@nvidia.com>");
diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
index 33605c3..3ebfaa6 100644
--- a/include/drm/drm_panel.h
+++ b/include/drm/drm_panel.h
@@ -32,6 +32,7 @@ struct backlight_device;
struct device_node;
struct drm_connector;
struct drm_device;
+struct drm_dp_aux;
struct drm_panel;
struct display_timing;

@@ -64,8 +65,8 @@ enum drm_panel_orientation;
* the panel. This is the job of the .unprepare() function.
*
* Backlight can be handled automatically if configured using
- * drm_panel_of_backlight(). Then the driver does not need to implement the
- * functionality to enable/disable backlight.
+ * drm_panel_of_backlight() or drm_panel_dp_aux_backlight(). Then the driver
+ * does not need to implement the functionality to enable/disable backlight.
*/
struct drm_panel_funcs {
/**
@@ -144,8 +145,8 @@ struct drm_panel {
* Backlight device, used to turn on backlight after the call
* to enable(), and to turn off backlight before the call to
* disable().
- * backlight is set by drm_panel_of_backlight() and drivers
- * shall not assign it.
+ * backlight is set by drm_panel_of_backlight() or
+ * drm_panel_dp_aux_backlight() and drivers shall not assign it.
*/
struct backlight_device *backlight;

@@ -208,11 +209,17 @@ static inline int of_drm_get_panel_orientation(const struct device_node *np,
#if IS_ENABLED(CONFIG_DRM_PANEL) && (IS_BUILTIN(CONFIG_BACKLIGHT_CLASS_DEVICE) || \
(IS_MODULE(CONFIG_DRM) && IS_MODULE(CONFIG_BACKLIGHT_CLASS_DEVICE)))
int drm_panel_of_backlight(struct drm_panel *panel);
+int drm_panel_dp_aux_backlight(struct drm_panel *panel, struct drm_dp_aux *aux);
#else
static inline int drm_panel_of_backlight(struct drm_panel *panel)
{
return 0;
}
+static inline int drm_panel_dp_aux_backlight(struct drm_panel *panel,
+ struct drm_dp_aux *aux)
+{
+ return 0;
+}
#endif

#endif
--
2.7.4