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

[Jani Nikula <jani.nikula@linux.intel.com>]

On Wed, 14 Feb 2024, Mario Limonciello <mario.limonciello@amd.com> 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.

I just replied to a previous version of the patch [1]. Looks like all
the comments there still hold.

BR,
Jani.


[1] https://lore.kernel.org/r/87eddd6d41.fsf@intel.com


>
> 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;
> +	}
> +
> +	/* 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)
> +		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;
>  };
>  
>  #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__ */

-- 
Jani Nikula, Intel