Hi Thomas,
On 6/23/24 10:51 AM, Thomas Weißschuh wrote:
> Panels using a PWM-controlled backlight source without an 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 valid backlight ranges can be
> maintained as part of the kernel.
>
> Signed-off-by: Thomas Weißschuh <linux@xxxxxxxxxxxxxx>
> ---
> 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 | 67 ++++++++++++++++++++++++++++
> include/drm/drm_utils.h | 11 +++++
> 5 files changed, 86 insertions(+)
>
> diff --git a/Documentation/gpu/drm-kms-helpers.rst b/Documentation/gpu/drm-kms-helpers.rst
> index 59cfe8a7a8ba..1998a2675210 100644
> --- a/Documentation/gpu/drm-kms-helpers.rst
> +++ b/Documentation/gpu/drm-kms-helpers.rst
> @@ -224,6 +224,9 @@ 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 959b19a04101..50ccb43315bf 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -443,6 +443,10 @@ config DRM_EXPORT_FOR_TESTS
> config DRM_PANEL_ORIENTATION_QUIRKS
> tristate
>
> +# 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 f9ca4f8fa6c5..6669913b907e 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..a89b5fd1940e
> --- /dev/null
> +++ b/drivers/gpu/drm/drm_panel_backlight_quirks.c
> @@ -0,0 +1,67 @@
> +// 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_connector.h>
> +#include <drm/drm_utils.h>
> +
> +struct drm_panel_backlight_entry {
> + struct {
> + enum dmi_field field;
> + const char * const value;
> + } dmi_match;
Matching on a single DMI string is not always enough to uniquely identify
a machine. I would change this to a dmi_system_id struct and then add
an array with 2 dmi_system_id structs in drm_panel_backlight_entry_matches()
and copy the struct to the first array entry + zero out the second entry
(terminator) and then use dmi_check_system().
> + struct drm_edid_ident ident;
Hmm, what about DSI panels? These do not (always) have EDID info AFAIK.
drivers/gpu/drm/drm_panel_orientation_quirks.c is using a resolution match
so as to hopefully not match external screens, but that is also so that it can
be used from efifb / simpledrm and here you really do want to differentiate
between different panels by panel model.
So I guess that the EDId match is fine and if we ever need to match DSI panels
without EDID we figure something out then.
Thinking more about this I have a question about the approach as a whole though,
I'll reply to the cover-letter with this.
Regards,
Hans
> + struct drm_panel_backlight_quirk quirk;
> +};
> +
> +static const struct drm_panel_backlight_entry drm_panel_backlight_entries[] = {
> +};
> +
> +static bool drm_panel_backlight_entry_matches(const struct drm_panel_backlight_entry *entry,
> + const struct drm_edid *edid)
> +{
> + if (!dmi_match(entry->dmi_match.field, entry->dmi_match.value))
> + return false;
> +
> + if (!drm_edid_match(edid, &entry->ident))
> + return false;
> +
> + return true;
> +}
> +
> +/**
> + * drm_get_panel_panel_quirk - Check for panel backlight quirks
> + * @edid: EDID of the panel to check
> + *
> + * This function checks for platform specific (e.g. DMI based) quirks
> + * providing info on backlight control for systems where this cannot be
> + * probed from the hard-/firm-ware.
> + *
> + * Returns:
> + * A struct drm_panel_backlight_quirk if a quirk is found or NULL otherwise.
> + */
> +const struct drm_panel_backlight_quirk *drm_get_panel_backlight_quirk(const struct drm_edid *edid)
> +{
> + const struct drm_panel_backlight_entry *entry;
> + size_t i;
> +
> + if (!IS_ENABLED(CONFIG_DMI))
> + return NULL;
> +
> + if (!edid)
> + return NULL;
> +
> + for (i = 0; i < ARRAY_SIZE(drm_panel_backlight_entries); i++) {
> + entry = &drm_panel_backlight_entries[i];
> +
> + if (drm_panel_backlight_entry_matches(entry, edid))
> + return &entry->quirk;
> + }
> +
> + return NULL;
> +}
> +EXPORT_SYMBOL(drm_get_panel_backlight_quirk);
> +
> +MODULE_LICENSE("GPL");
> diff --git a/include/drm/drm_utils.h b/include/drm/drm_utils.h
> index 70775748d243..37cc6de1a01a 100644
> --- a/include/drm/drm_utils.h
> +++ b/include/drm/drm_utils.h
> @@ -11,9 +11,20 @@
> #define __DRM_UTILS_H__
>
> #include <linux/types.h>
> +#include <drm/drm_edid.h>
> +
> +struct drm_panel_backlight_quirk {
> + struct {
> + bool pwm_min_brightness:1;
> + } overrides;
> +
> + u8 pwm_min_brightness; /* min_brightness/255 of max */
> +};
>
> int drm_get_panel_orientation_quirk(int width, int height);
>
> +const struct drm_panel_backlight_quirk *drm_get_panel_backlight_quirk(const struct drm_edid *edid);
> +
> signed long drm_timeout_abs_to_jiffies(int64_t timeout_nsec);
>
> #endif
>
