drm: Add panel backlight quirks

Panels using a PWM-controlled backlight source do not have a standard
way to communicate their valid PWM ranges.
On x86 the ranges are read from ACPI through driver-specific tables.
The built-in ranges are not necessarily correct, or may grow stale if an
older device can be retrofitted with newer panels.

Add a quirk infrastructure with which the minimum valid backlight value
can be maintained as part of the kernel.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Tested-by: Dustin L. Howett <dustin@howett.net>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241111-amdgpu-min-backlight-quirk-v7-1-f662851fda69@weissschuh.net

diff --git a/Documentation/gpu/drm-kms-helpers.rst b/Documentation/gpu/drm-kms-helpers.rst
index 8cf2f041af4704875910ce8228ae04615d0f21bd..b4ee25af1702b0019e0de5f9ee66d2dbdac2c664 100644 (file)
--- a/Documentation/gpu/drm-kms-helpers.rst
+++ b/Documentation/gpu/drm-kms-helpers.rst
@@ -221,6 +221,9 @@ Panel Helper Reference
 .. kernel-doc:: drivers/gpu/drm/drm_panel_orientation_quirks.c
    :export:
 
+.. kernel-doc:: drivers/gpu/drm/drm_panel_backlight_quirks.c
+   :export:
+
 Panel Self Refresh Helper Reference
 ===================================
 

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index fd294ccca6bb79e724f43ebda1403920c6ed7322..698981a2ed51e254d0a9bfe6ecf2769f62ac893c 100644 (file)
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -456,6 +456,10 @@ config DRM_HYPERV
 config DRM_EXPORT_FOR_TESTS
        bool
 
+# Separate option as not all DRM drivers use it
+config DRM_PANEL_BACKLIGHT_QUIRKS
+       tristate
+
 config DRM_LIB_RANDOM
        bool
        default n

diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
index 4f6585be14ccf9b5a47afde81f8bbec8b80a0be6..1677c1f335fbb0c6114bdb4cc0b12eb407d84564 100644 (file)
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -95,6 +95,7 @@ drm-$(CONFIG_DRM_PANIC_SCREEN_QR_CODE) += drm_panic_qr.o
 obj-$(CONFIG_DRM)      += drm.o
 
 obj-$(CONFIG_DRM_PANEL_ORIENTATION_QUIRKS) += drm_panel_orientation_quirks.o
+obj-$(CONFIG_DRM_PANEL_BACKLIGHT_QUIRKS) += drm_panel_backlight_quirks.o
 
 #
 # Memory-management helpers

diff --git a/drivers/gpu/drm/drm_panel_backlight_quirks.c b/drivers/gpu/drm/drm_panel_backlight_quirks.c
new file mode 100644 (file)
index 0000000..6b8bbed
--- /dev/null
+++ b/drivers/gpu/drm/drm_panel_backlight_quirks.c
@@ -0,0 +1,70 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/array_size.h>
+#include <linux/dmi.h>
+#include <linux/mod_devicetable.h>
+#include <linux/module.h>
+#include <drm/drm_edid.h>
+#include <drm/drm_utils.h>
+
+struct drm_panel_min_backlight_quirk {
+       struct {
+               enum dmi_field field;
+               const char * const value;
+       } dmi_match;
+       struct drm_edid_ident ident;
+       u8 min_brightness;
+};
+
+static const struct drm_panel_min_backlight_quirk drm_panel_min_backlight_quirks[] = {
+};
+
+static bool drm_panel_min_backlight_quirk_matches(const struct drm_panel_min_backlight_quirk *quirk,
+                                                 const struct drm_edid *edid)
+{
+       if (!dmi_match(quirk->dmi_match.field, quirk->dmi_match.value))
+               return false;
+
+       if (!drm_edid_match(edid, &quirk->ident))
+               return false;
+
+       return true;
+}
+
+/**
+ * drm_get_panel_min_brightness_quirk - Get minimum supported brightness level for a panel.
+ * @edid: EDID of the panel to check
+ *
+ * This function checks for platform specific (e.g. DMI based) quirks
+ * providing info on the minimum backlight brightness for systems where this
+ * cannot be probed correctly from the hard-/firm-ware.
+ *
+ * Returns:
+ * A negative error value or
+ * an override value in the range [0, 255] representing 0-100% to be scaled to
+ * the drivers target range.
+ */
+int drm_get_panel_min_brightness_quirk(const struct drm_edid *edid)
+{
+       const struct drm_panel_min_backlight_quirk *quirk;
+       size_t i;
+
+       if (!IS_ENABLED(CONFIG_DMI))
+               return -ENODATA;
+
+       if (!edid)
+               return -EINVAL;
+
+       for (i = 0; i < ARRAY_SIZE(drm_panel_min_backlight_quirks); i++) {
+               quirk = &drm_panel_min_backlight_quirks[i];
+
+               if (drm_panel_min_backlight_quirk_matches(quirk, edid))
+                       return quirk->min_brightness;
+       }
+
+       return -ENODATA;
+}
+EXPORT_SYMBOL(drm_get_panel_min_brightness_quirk);
+
+MODULE_DESCRIPTION("Quirks for panel backlight overrides");
+MODULE_LICENSE("GPL");

diff --git a/include/drm/drm_utils.h b/include/drm/drm_utils.h
index 70775748d243b0fd6e13a088d05c45f31cf34a4a..15fa9b6865f448cc8338c935874015fd74cb7bb2 100644 (file)
--- a/include/drm/drm_utils.h
+++ b/include/drm/drm_utils.h
@@ -12,8 +12,12 @@
 
 #include <linux/types.h>
 
+struct drm_edid;
+
 int drm_get_panel_orientation_quirk(int width, int height);
 
+int drm_get_panel_min_brightness_quirk(const struct drm_edid *edid);
+
 signed long drm_timeout_abs_to_jiffies(int64_t timeout_nsec);
 
 #endif