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Date: Mon, 12 Feb 2024 10:31:12 -0600
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Subject: Re: [PATCH v5 1/3] drm: Add support to get EDID from ACPI
To: amd-gfx@lists.freedesktop.org,
 "open list:DRM DRIVERS" <dri-devel@lists.freedesktop.org>
Cc: "open list:ACPI" <linux-acpi@vger.kernel.org>,
 open list <linux-kernel@vger.kernel.org>, Melissa Wen <mwen@igalia.com>,
 Mark Pearson <mpearson-lenovo@squebb.ca>
References: <20240211055011.3583-1-mario.limonciello@amd.com>
 <20240211055011.3583-2-mario.limonciello@amd.com>
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From: Mario Limonciello <mario.limonciello@amd.com>
In-Reply-To: <20240211055011.3583-2-mario.limonciello@amd.com>
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On 2/10/2024 23:50, 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>
> ---
> v1->v2:
>   * Split code from previous amdgpu specific helper to generic drm helper.
> v2->v3:
>   * Add an extra select to fix a variety of randconfig errors found from
>     LKP robot.
> v3->v4:
>   * Return struct drm_edid
> v4->v5:
>   * Rename to drm_edid_read_acpi
>   * Drop selects
> ---
>   drivers/gpu/drm/Kconfig     |   7 +++
>   drivers/gpu/drm/drm_edid.c  | 113 +++++++++++++++++++++++++++++++++---
>   include/drm/drm_connector.h |   6 ++
>   include/drm/drm_edid.h      |   1 +
>   4 files changed, 119 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index 2520db0b776e..a49740c528b9 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -103,6 +103,13 @@ config DRM_KMS_HELPER
>   	help
>   	  CRTC helpers for KMS drivers.
>   
> +config DRM_ACPI_HELPER
> +	tristate "ACPI support in DRM"
> +	depends on DRM
> +	depends on (ACPI_VIDEO || ACPI_VIDEO=n)
> +	help
> +	  ACPI helpers for DRM drivers.
> +

Unfortunately in my wider testing this still fails with a few combinations.

This combination fails to link:

CONFIG_ACPI_VIDEO=m
CONFIG_DRM_ACPI_HELPER=y
CONFIG_DRM=y

This combination links but doesn't work because the IS_REACHABLE() fails 
(-EOPNOTSUPP):

CONFIG_ACPI_VIDEO=m
CONFIG_DRM_ACPI_HELPER=M
CONFIG_DRM=y

I'm tempted to split off all of drm_edid to it's own module instead  of 
CONFIG_DRM_ACPI_HELPER which has a depends on (ACPI_VIDEO || ACPI_VIDEIO=n).

Or Daniel, any better ideas?

>   config DRM_DEBUG_DP_MST_TOPOLOGY_REFS
>           bool "Enable refcount backtrace history in the DP MST helpers"
>   	depends on STACKTRACE_SUPPORT
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 69c68804023f..096c278b6f66 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 +2189,62 @@ 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 */
> +	if (IS_REACHABLE(CONFIG_DRM_ACPI_HELPER)) {
> +		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 -EINVAL;
> +		}
> +	} else {
> +		r = -EOPNOTSUPP;
> +	}
> +	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 +2678,8 @@ 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 +2687,50 @@ 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 +2815,11 @@ 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 +2831,18 @@ 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 518d1b8106c7..38b5e1b5c773 100644
> --- a/include/drm/drm_edid.h
> +++ b/include/drm/drm_edid.h
> @@ -463,5 +463,6 @@ 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__ */