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

[Mario Limonciello <mario.limonciello@amd.com>]

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
>