Re: [PATCH v6 3/5] drm: Add support to get EDID from ACPI

Mario Limonciello
2024-02-15T18:21:01Z

On 2/14/2024 17:13, Ville Syrjälä wrote:
> On Wed, Feb 14, 2024 at 03:57:54PM -0600, Mario Limonciello wrote:
>> Some manufacturers have intentionally put an EDID that differs from
>> the EDID on the internal panel on laptops. Drivers that prefer to
>> fetch this EDID can set a bit on the drm_connector to indicate that
>> the DRM EDID helpers should try to fetch it and it is preferred if
>> it's present.
>>
>> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
>> ---
>> drivers/gpu/drm/Kconfig | 1 +
>> drivers/gpu/drm/drm_edid.c | 109 +++++++++++++++++++++++++++++++++---
>> include/drm/drm_connector.h | 6 ++
>> include/drm/drm_edid.h | 1 +
>> 4 files changed, 109 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
>> index 872edb47bb53..3db89e6af01d 100644
>> --- a/drivers/gpu/drm/Kconfig
>> +++ b/drivers/gpu/drm/Kconfig
>> @@ -8,6 +8,7 @@
>> menuconfig DRM
>> tristate "Direct Rendering Manager (XFree86 4.1.0 and higher DRI support)"
>> depends on (AGP || AGP=n) && !EMULATED_CMPXCHG && HAS_DMA
>> + depends on (ACPI_VIDEO || ACPI_VIDEO=n)
>> select DRM_PANEL_ORIENTATION_QUIRKS
>> select DRM_KMS_HELPER if DRM_FBDEV_EMULATION
>> select FB_CORE if DRM_FBDEV_EMULATION
>> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
>> index 923c4423151c..cdc30c6d05d5 100644
>> --- a/drivers/gpu/drm/drm_edid.c
>> +++ b/drivers/gpu/drm/drm_edid.c
>> @@ -28,6 +28,7 @@
>> * DEALINGS IN THE SOFTWARE.
>> */
>>
>> +#include <acpi/video.h>
>> #include <linux/bitfield.h>
>> #include <linux/cec.h>
>> #include <linux/hdmi.h>
>> @@ -2188,6 +2189,58 @@ drm_do_probe_ddc_edid(void *data, u8 *buf, unsigned int block, size_t len)
>> return ret == xfers ? 0 : -1;
>> }
>>
>> +/**
>> + * drm_do_probe_acpi_edid() - get EDID information via ACPI _DDC
>> + * @data: struct drm_connector
>> + * @buf: EDID data buffer to be filled
>> + * @block: 128 byte EDID block to start fetching from
>> + * @len: EDID data buffer length to fetch
>> + *
>> + * Try to fetch EDID information by calling acpi_video_get_edid() function.
>> + *
>> + * Return: 0 on success or error code on failure.
>> + */
>> +static int
>> +drm_do_probe_acpi_edid(void *data, u8 *buf, unsigned int block, size_t len)
>> +{
>> + struct drm_connector *connector = data;
>> + struct drm_device *ddev = connector->dev;
>> + struct acpi_device *acpidev = ACPI_COMPANION(ddev->dev);
>> + unsigned char start = block * EDID_LENGTH;
>> + void *edid;
>> + int r;
>> +
>> + if (!acpidev)
>> + return -ENODEV;
>> +
>> + switch (connector->connector_type) {
>> + case DRM_MODE_CONNECTOR_LVDS:
>> + case DRM_MODE_CONNECTOR_eDP:
>> + break;
>> + default:
>> + return -EINVAL;
>> + }
>
> We could have other types of connectors that want this too.
> I don't see any real benefit in having this check tbh. Drivers
> should simply notset the flag on connectors where it won't work,
> and only the driver can really know that.

Ack.

>
>> + /* fetch the entire edid from BIOS */
>> + r = acpi_video_get_edid(acpidev, ACPI_VIDEO_DISPLAY_LCD, -1, &edid);
>> + if (r < 0) {
>> + DRM_DEBUG_KMS("Failed to get EDID from ACPI: %d\n", r);
>> + return r;
>> + }
>> + if (len > r || start > r || start + len > r) {
>> + r = -EINVAL;
>> + goto cleanup;
>> + }
>> +
>> + memcpy(buf, edid + start, len);
>> + r = 0;
>> +
>> +cleanup:
>> + kfree(edid);
>> +
>> + return r;
>> +}
>> +
>> static void connector_bad_edid(struct drm_connector *connector,
>> const struct edid *edid, int num_blocks)
>> {
>> @@ -2621,7 +2674,8 @@ EXPORT_SYMBOL(drm_probe_ddc);
>> * @connector: connector we're probing
>> * @adapter: I2C adapter to use for DDC
>> *
>> - * Poke the given I2C channel to grab EDID data if possible. If found,
>> + * If the connector allows it, try to fetch EDID data using ACPI. If not found
>> + * poke the given I2C channel to grab EDID data if possible. If found,
>> * attach it to the connector.
>> *
>> * Return: Pointer to valid EDID or NULL if we couldn't find any.
>> @@ -2629,20 +2683,50 @@ EXPORT_SYMBOL(drm_probe_ddc);
>> struct edid *drm_get_edid(struct drm_connector *connector,
>> struct i2c_adapter *adapter)
>> {
>> - struct edid *edid;
>> + struct edid *edid = NULL;
>>
>> if (connector->force == DRM_FORCE_OFF)
>> return NULL;
>>
>> - if (connector->force == DRM_FORCE_UNSPECIFIED && !drm_probe_ddc(adapter))
>> - return NULL;
>> + if (connector->acpi_edid_allowed)
>> + edid = _drm_do_get_edid(connector, drm_do_probe_acpi_edid, connector, NULL);
>> +
>> + if (!edid) {
>> + if (connector->force == DRM_FORCE_UNSPECIFIED && !drm_probe_ddc(adapter))
>> + return NULL;
>> + edid = _drm_do_get_edid(connector, drm_do_probe_ddc_edid, adapter, NULL);
>> + }
>>
>> - edid = _drm_do_get_edid(connector, drm_do_probe_ddc_edid, adapter, NULL);
>> drm_connector_update_edid_property(connector, edid);
>> return edid;
>> }
>> EXPORT_SYMBOL(drm_get_edid);
>>
>> +/**
>> + * drm_edid_read_acpi - get EDID data, if available
>> + * @connector: connector we're probing
>> + *
>> + * Use the BIOS to attempt to grab EDID data if possible.
>> + *
>> + * The returned pointer must be freed using drm_edid_free().
>> + *
>> + * Return: Pointer to valid EDID or NULL if we couldn't find any.
>> + */
>> +const struct drm_edid *drm_edid_read_acpi(struct drm_connector *connector)
>> +{
>> + const struct drm_edid *drm_edid;
>> +
>> + if (connector->force == DRM_FORCE_OFF)
>> + return NULL;
>> +
>> + drm_edid = drm_edid_read_custom(connector, drm_do_probe_acpi_edid, connector);
>> +
>> + /* Note: Do *not* call connector updates here. */
>> +
>> + return drm_edid;
>> +}
>> +EXPORT_SYMBOL(drm_edid_read_acpi);
>> +
>> /**
>> * drm_edid_read_custom - Read EDID data using given EDID block read function
>> * @connector: Connector to use
>> @@ -2727,10 +2811,11 @@ const struct drm_edid *drm_edid_read_ddc(struct drm_connector *connector,
>> EXPORT_SYMBOL(drm_edid_read_ddc);
>>
>> /**
>> - * drm_edid_read - Read EDID data using connector's I2C adapter
>> + * drm_edid_read - Read EDID data using BIOS or connector's I2C adapter
>> * @connector: Connector to use
>> *
>> - * Read EDID using the connector's I2C adapter.
>> + * Read EDID from BIOS if allowed by connector or by using the connector's
>> + * I2C adapter.
>> *
>> * The EDID may be overridden using debugfs override_edid or firmware EDID
>> * (drm_edid_load_firmware() and drm.edid_firmware parameter), in this priority
>> @@ -2742,10 +2827,18 @@ EXPORT_SYMBOL(drm_edid_read_ddc);
>> */
>> const struct drm_edid *drm_edid_read(struct drm_connector *connector)
>> {
>> + const struct drm_edid *drm_edid = NULL;
>> +
>> if (drm_WARN_ON(connector->dev, !connector->ddc))
>> return NULL;
>>
>> - return drm_edid_read_ddc(connector, connector->ddc);
>> + if (connector->acpi_edid_allowed)
>
> That should probably be called 'prefer_acpi_edid' or something
> since it's the first choice when the flag is set.

OK.

>
> But I'm not so sure there's any real benefit in having this
> flag at all. You anyway have to modify the driver to use this,
> so why not just have the driver do the call directly instead of
> adding this extra detour via the flag?

This was proposed by Maxime Ripard during v4.

https://lore.kernel.org/dri-devel/ysm2e3vczov7z7vezmexe35fjnkhsakud3elsgggedhk2lknlz@cx7j44y354db/

>
>> + drm_edid = drm_edid_read_acpi(connector);
>> +
>> + if (!drm_edid)
>> + drm_edid = drm_edid_read_ddc(connector, connector->ddc);
>> +
>> + return drm_edid;
>> }
>> EXPORT_SYMBOL(drm_edid_read);
>>
>> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
>> index fe88d7fc6b8f..74ed47f37a69 100644
>> --- a/include/drm/drm_connector.h
>> +++ b/include/drm/drm_connector.h
>> @@ -1886,6 +1886,12 @@ struct drm_connector {
>>
>> /** @hdr_sink_metadata: HDR Metadata Information read from sink */
>> struct hdr_sink_metadata hdr_sink_metadata;
>> +
>> + /**
>> + * @acpi_edid_allowed: Get the EDID from the BIOS, if available.
>> + * This is only applicable to eDP and LVDS displays.
>> + */
>> + bool acpi_edid_allowed;
>
> Aren't there other bools/small stuff in there for tighter packing?

Does the compiler automatically do the packing if you put bools nearby
in a struct? If so; TIL.

>
>> };
>>
>> #define obj_to_connector(x) container_of(x, struct drm_connector, base)
>> diff --git a/include/drm/drm_edid.h b/include/drm/drm_edid.h
>> index 7923bc00dc7a..1c1ee927de9c 100644
>> --- a/include/drm/drm_edid.h
>> +++ b/include/drm/drm_edid.h
>> @@ -459,5 +459,6 @@ bool drm_edid_is_digital(const struct drm_edid *drm_edid);
>>
>> const u8 *drm_find_edid_extension(const struct drm_edid *drm_edid,
>> int ext_id, int *ext_index);
>> +const struct drm_edid *drm_edid_read_acpi(struct drm_connector *connector);
>>
>> #endif /* __DRM_EDID_H__ */
>> --
>> 2.34.1
>