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@xxxxxxxxxxxxxx>
Tested-by: Dustin L. Howett <dustin@xxxxxxxxxx>
---
Documentation/gpu/drm-kms-helpers.rst | 3 ++
drivers/gpu/drm/Kconfig | 4 ++
drivers/gpu/drm/Makefile | 1 +
drivers/gpu/drm/drm_panel_backlight_quirks.c | 70 ++++++++++++++++++++++++++++
include/drm/drm_utils.h | 4 ++
5 files changed, 82 insertions(+)
diff --git a/Documentation/gpu/drm-kms-helpers.rst b/Documentation/gpu/drm-kms-helpers.rst
index 8435e8621cc0..a26989500129 100644
--- a/Documentation/gpu/drm-kms-helpers.rst
+++ b/Documentation/gpu/drm-kms-helpers.rst
@@ -230,6 +230,9 @@ 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 6b2c6b91f962..9ebb8cdb535e 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -454,6 +454,10 @@ 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 68cc9258ffc4..adf85999aee2 100644
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -92,6 +92,7 @@ drm-$(CONFIG_DRM_PANIC) += drm_panic.o
obj-$(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
index 000000000000..6b8bbed77c7f
--- /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 70775748d243..15fa9b6865f4 100644
--- 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
--
2.46.0
