diff mbox series

[v7,3/5] drm/edid: read HF-EEODB ext block

Message ID 20220313134702.24175-4-shawn.c.lee@intel.com (mailing list archive)
State New, archived
Headers show
Series enhanced edid driver compatibility | expand

Commit Message

Lee Shawn C March 13, 2022, 1:47 p.m. UTC
According to HDMI 2.1 spec.

"The HDMI Forum EDID Extension Override Data Block (HF-EEODB)
is utilized by Sink Devices to provide an alternate method to
indicate an EDID Extension Block count larger than 1, while
avoiding the need to present a VESA Block Map in the first
E-EDID Extension Block."

It is a mandatory for HDMI 2.1 protocol compliance as well.
This patch help to know how many HF_EEODB blocks report by sink
and read allo HF_EEODB blocks back.

v2: support to find CEA block, check EEODB block format, and return
    available block number in drm_edid_read_hf_eeodb_blk_count().

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Cc: Drew Davenport <ddavenport@chromium.org>
Cc: intel-gfx <intel-gfx@lists.freedesktop.org>
Signed-off-by: Lee Shawn C <shawn.c.lee@intel.com>
---
 drivers/gpu/drm/drm_connector.c |  8 +++-
 drivers/gpu/drm/drm_edid.c      | 71 +++++++++++++++++++++++++++++++--
 include/drm/drm_edid.h          |  1 +
 3 files changed, 74 insertions(+), 6 deletions(-)

Comments

Jani Nikula March 15, 2022, 11:03 a.m. UTC | #1
On Sun, 13 Mar 2022, Lee Shawn C <shawn.c.lee@intel.com> wrote:
> According to HDMI 2.1 spec.
>
> "The HDMI Forum EDID Extension Override Data Block (HF-EEODB)
> is utilized by Sink Devices to provide an alternate method to
> indicate an EDID Extension Block count larger than 1, while
> avoiding the need to present a VESA Block Map in the first
> E-EDID Extension Block."
>
> It is a mandatory for HDMI 2.1 protocol compliance as well.
> This patch help to know how many HF_EEODB blocks report by sink
> and read allo HF_EEODB blocks back.
>
> v2: support to find CEA block, check EEODB block format, and return
>     available block number in drm_edid_read_hf_eeodb_blk_count().
>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
> Cc: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> Cc: Drew Davenport <ddavenport@chromium.org>
> Cc: intel-gfx <intel-gfx@lists.freedesktop.org>
> Signed-off-by: Lee Shawn C <shawn.c.lee@intel.com>
> ---
>  drivers/gpu/drm/drm_connector.c |  8 +++-
>  drivers/gpu/drm/drm_edid.c      | 71 +++++++++++++++++++++++++++++++--
>  include/drm/drm_edid.h          |  1 +
>  3 files changed, 74 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> index a50c82bc2b2f..16011023c12e 100644
> --- a/drivers/gpu/drm/drm_connector.c
> +++ b/drivers/gpu/drm/drm_connector.c
> @@ -2129,7 +2129,7 @@ int drm_connector_update_edid_property(struct drm_connector *connector,
>  				       const struct edid *edid)
>  {
>  	struct drm_device *dev = connector->dev;
> -	size_t size = 0;
> +	size_t size = 0, hf_eeodb_blk_count;
>  	int ret;
>  	const struct edid *old_edid;
>  
> @@ -2137,8 +2137,12 @@ int drm_connector_update_edid_property(struct drm_connector *connector,
>  	if (connector->override_edid)
>  		return 0;
>  
> -	if (edid)
> +	if (edid) {
>  		size = EDID_LENGTH * (1 + edid->extensions);
> +		hf_eeodb_blk_count = drm_edid_read_hf_eeodb_blk_count(edid);
> +		if (hf_eeodb_blk_count)
> +			size = EDID_LENGTH * (1 + hf_eeodb_blk_count);

This approach does not scale. If the number of extensions and thus the
total EDID size depend on HF-EEODB, this *must* be abstracted.

Consider, for example, drm_edid_duplicate(), which only looks at
edid->extensions. A subsequent HF-EEODB aware access on an EDID
duplicated using drm_edid_duplicate() will access beyond the allocated
buffer.

Yes, it's a lot of work to introduce drm_edid_size() and
drm_edid_extension_count() or similar, and use them everywhere, but this
is what we must do. It's a lot more work to try to take HF-EEODB into
account everywhere. The latter is going to be riddled with bugs with
everyone doing it a little different.

> +	}
>  
>  	/* Set the display info, using edid if available, otherwise
>  	 * resetting the values to defaults. This duplicates the work
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 9fa84881fbba..5ae4e83fa5e3 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -1992,6 +1992,7 @@ struct edid *drm_do_get_edid(struct drm_connector *connector,
>  {
>  	int i, j = 0, valid_extensions = 0;
>  	u8 *edid, *new;
> +	size_t hf_eeodb_blk_count;
>  	struct edid *override;
>  
>  	override = drm_get_override_edid(connector);
> @@ -2051,7 +2052,35 @@ struct edid *drm_do_get_edid(struct drm_connector *connector,
>  		}
>  
>  		kfree(edid);
> +		return (struct edid *)new;
> +	}
> +
> +	hf_eeodb_blk_count = drm_edid_read_hf_eeodb_blk_count((struct edid *)edid);
> +	if (hf_eeodb_blk_count >= 2) {
> +		new = krealloc(edid, (hf_eeodb_blk_count + 1) * EDID_LENGTH, GFP_KERNEL);
> +		if (!new)
> +			goto out;
>  		edid = new;
> +
> +		valid_extensions = hf_eeodb_blk_count - 1;
> +		for (j = 2; j <= hf_eeodb_blk_count; j++) {
> +			u8 *block = edid + j * EDID_LENGTH;
> +
> +			for (i = 0; i < 4; i++) {
> +				if (get_edid_block(data, block, j, EDID_LENGTH))
> +					goto out;
> +				if (drm_edid_block_valid(block, j, false, NULL))
> +					break;
> +			}
> +
> +			if (i == 4)
> +				valid_extensions--;
> +		}
> +
> +		if (valid_extensions != hf_eeodb_blk_count - 1) {
> +			DRM_ERROR("Not able to retrieve proper EDID contain HF-EEODB data.\n");
> +			goto out;
> +		}
>  	}
>  
>  	return (struct edid *)edid;
> @@ -3315,15 +3344,17 @@ add_detailed_modes(struct drm_connector *connector, struct edid *edid,
>  #define VIDEO_BLOCK     0x02
>  #define VENDOR_BLOCK    0x03
>  #define SPEAKER_BLOCK	0x04
> -#define HDR_STATIC_METADATA_BLOCK	0x6
> -#define USE_EXTENDED_TAG 0x07
> -#define EXT_VIDEO_CAPABILITY_BLOCK 0x00
> +#define EXT_VIDEO_CAPABILITY_BLOCK	0x00
> +#define HDR_STATIC_METADATA_BLOCK	0x06
> +#define USE_EXTENDED_TAG		0x07
>  #define EXT_VIDEO_DATA_BLOCK_420	0x0E
> -#define EXT_VIDEO_CAP_BLOCK_Y420CMDB 0x0F
> +#define EXT_VIDEO_CAP_BLOCK_Y420CMDB	0x0F
> +#define EXT_VIDEO_HF_EEODB_DATA_BLOCK	0x78
>  #define EDID_BASIC_AUDIO	(1 << 6)
>  #define EDID_CEA_YCRCB444	(1 << 5)
>  #define EDID_CEA_YCRCB422	(1 << 4)
>  #define EDID_CEA_VCDB_QS	(1 << 6)
> +#define HF_EEODB_LENGTH		2
>  
>  /*
>   * Search EDID for CEA extension block.
> @@ -4274,9 +4305,41 @@ static bool cea_db_is_y420vdb(const u8 *db)
>  	return true;
>  }
>  
> +static bool cea_db_is_hdmi_forum_eeodb(const u8 *db)
> +{
> +	if (cea_db_tag(db) != USE_EXTENDED_TAG)
> +		return false;
> +
> +	if (cea_db_payload_len(db) != HF_EEODB_LENGTH)
> +		return false;
> +
> +	if (cea_db_extended_tag(db) != EXT_VIDEO_HF_EEODB_DATA_BLOCK)
> +		return false;
> +
> +	return true;
> +}
> +
>  #define for_each_cea_db(cea, i, start, end) \
>  	for ((i) = (start); (i) < (end) && (i) + cea_db_payload_len(&(cea)[(i)]) < (end); (i) += cea_db_payload_len(&(cea)[(i)]) + 1)
>  
> +size_t drm_edid_read_hf_eeodb_blk_count(const struct edid *edid)
> +{
> +	const u8 *cea;
> +	int i, start, end, cea_ext_index = 0, displayid_ext_index = 0;
> +
> +	if (edid->extensions) {
> +		cea = drm_find_cea_extension(edid, &cea_ext_index, &displayid_ext_index);
> +
> +		if (cea && !cea_db_offsets(cea, &start, &end))
> +			for_each_cea_db(cea, i, start, end)
> +				if (cea_db_is_hdmi_forum_eeodb(&cea[i]))
> +					return cea[i + 2];
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(drm_edid_read_hf_eeodb_blk_count);

This should be static and not exported.

BR,
Jani.

> +
>  static void drm_parse_y420cmdb_bitmap(struct drm_connector *connector,
>  				      const u8 *db)
>  {
> diff --git a/include/drm/drm_edid.h b/include/drm/drm_edid.h
> index 144c495b99c4..585f0ed932d4 100644
> --- a/include/drm/drm_edid.h
> +++ b/include/drm/drm_edid.h
> @@ -593,5 +593,6 @@ drm_display_mode_from_cea_vic(struct drm_device *dev,
>  const u8 *drm_find_edid_extension(const struct edid *edid,
>  				  int ext_id, int *ext_index);
>  
> +size_t drm_edid_read_hf_eeodb_blk_count(const struct edid *edid);
>  
>  #endif /* __DRM_EDID_H__ */
Lee Shawn C March 15, 2022, 1:43 p.m. UTC | #2
On Tuesday, March 15, 2022 7:03 PM, Nikula, Jani <jani.nikula@intel.com> wrote:
>On Sun, 13 Mar 2022, Lee Shawn C <shawn.c.lee@intel.com> wrote:
>> According to HDMI 2.1 spec.
>>
>> "The HDMI Forum EDID Extension Override Data Block (HF-EEODB) is 
>> utilized by Sink Devices to provide an alternate method to indicate an 
>> EDID Extension Block count larger than 1, while avoiding the need to 
>> present a VESA Block Map in the first E-EDID Extension Block."
>>
>> It is a mandatory for HDMI 2.1 protocol compliance as well.
>> This patch help to know how many HF_EEODB blocks report by sink and 
>> read allo HF_EEODB blocks back.
>>
>> v2: support to find CEA block, check EEODB block format, and return
>>     available block number in drm_edid_read_hf_eeodb_blk_count().
>>
>> Cc: Jani Nikula <jani.nikula@linux.intel.com>
>> Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
>> Cc: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
>> Cc: Drew Davenport <ddavenport@chromium.org>
>> Cc: intel-gfx <intel-gfx@lists.freedesktop.org>
>> Signed-off-by: Lee Shawn C <shawn.c.lee@intel.com>
>> ---
>>  drivers/gpu/drm/drm_connector.c |  8 +++-
>>  drivers/gpu/drm/drm_edid.c      | 71 +++++++++++++++++++++++++++++++--
>>  include/drm/drm_edid.h          |  1 +
>>  3 files changed, 74 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_connector.c 
>> b/drivers/gpu/drm/drm_connector.c index a50c82bc2b2f..16011023c12e 
>> 100644
>> --- a/drivers/gpu/drm/drm_connector.c
>> +++ b/drivers/gpu/drm/drm_connector.c
>> @@ -2129,7 +2129,7 @@ int drm_connector_update_edid_property(struct drm_connector *connector,
>>  				       const struct edid *edid)
>>  {
>>  	struct drm_device *dev = connector->dev;
>> -	size_t size = 0;
>> +	size_t size = 0, hf_eeodb_blk_count;
>>  	int ret;
>>  	const struct edid *old_edid;
>>  
>> @@ -2137,8 +2137,12 @@ int drm_connector_update_edid_property(struct drm_connector *connector,
>>  	if (connector->override_edid)
>>  		return 0;
>>  
>> -	if (edid)
>> +	if (edid) {
>>  		size = EDID_LENGTH * (1 + edid->extensions);
>> +		hf_eeodb_blk_count = drm_edid_read_hf_eeodb_blk_count(edid);
>> +		if (hf_eeodb_blk_count)
>> +			size = EDID_LENGTH * (1 + hf_eeodb_blk_count);
>
>This approach does not scale. If the number of extensions and thus the total EDID size depend on HF-EEODB, this *must* be abstracted.
>
>Consider, for example, drm_edid_duplicate(), which only looks at
>edid->extensions. A subsequent HF-EEODB aware access on an EDID
>duplicated using drm_edid_duplicate() will access beyond the allocated buffer.
>
>Yes, it's a lot of work to introduce drm_edid_size() and
>drm_edid_extension_count() or similar, and use them everywhere, but this is what we must do. It's a lot more work to try to take HF-EEODB into account everywhere. The latter is going to be riddled with bugs with everyone doing it a little different.
>

As you mentioned, we should have new functions to provide proper EDID byte size or extension counter.
And reuse them to handle/retrieve EDID more accurately in drm driver. Thanks for your comment!

>> +	}
>>  
>>  	/* Set the display info, using edid if available, otherwise
>>  	 * resetting the values to defaults. This duplicates the work diff 
>> --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c index 
>> 9fa84881fbba..5ae4e83fa5e3 100644
>> --- a/drivers/gpu/drm/drm_edid.c
>> +++ b/drivers/gpu/drm/drm_edid.c
>> @@ -1992,6 +1992,7 @@ struct edid *drm_do_get_edid(struct 
>> drm_connector *connector,  {
>>  	int i, j = 0, valid_extensions = 0;
>>  	u8 *edid, *new;
>> +	size_t hf_eeodb_blk_count;
>>  	struct edid *override;
>>  
>>  	override = drm_get_override_edid(connector); @@ -2051,7 +2052,35 @@ 
>> struct edid *drm_do_get_edid(struct drm_connector *connector,
>>  		}
>>  
>>  		kfree(edid);
>> +		return (struct edid *)new;
>> +	}
>> +
>> +	hf_eeodb_blk_count = drm_edid_read_hf_eeodb_blk_count((struct edid *)edid);
>> +	if (hf_eeodb_blk_count >= 2) {
>> +		new = krealloc(edid, (hf_eeodb_blk_count + 1) * EDID_LENGTH, GFP_KERNEL);
>> +		if (!new)
>> +			goto out;
>>  		edid = new;
>> +
>> +		valid_extensions = hf_eeodb_blk_count - 1;
>> +		for (j = 2; j <= hf_eeodb_blk_count; j++) {
>> +			u8 *block = edid + j * EDID_LENGTH;
>> +
>> +			for (i = 0; i < 4; i++) {
>> +				if (get_edid_block(data, block, j, EDID_LENGTH))
>> +					goto out;
>> +				if (drm_edid_block_valid(block, j, false, NULL))
>> +					break;
>> +			}
>> +
>> +			if (i == 4)
>> +				valid_extensions--;
>> +		}
>> +
>> +		if (valid_extensions != hf_eeodb_blk_count - 1) {
>> +			DRM_ERROR("Not able to retrieve proper EDID contain HF-EEODB data.\n");
>> +			goto out;
>> +		}
>>  	}
>>  
>>  	return (struct edid *)edid;
>> @@ -3315,15 +3344,17 @@ add_detailed_modes(struct drm_connector *connector, struct edid *edid,
>>  #define VIDEO_BLOCK     0x02
>>  #define VENDOR_BLOCK    0x03
>>  #define SPEAKER_BLOCK	0x04
>> -#define HDR_STATIC_METADATA_BLOCK	0x6
>> -#define USE_EXTENDED_TAG 0x07
>> -#define EXT_VIDEO_CAPABILITY_BLOCK 0x00
>> +#define EXT_VIDEO_CAPABILITY_BLOCK	0x00
>> +#define HDR_STATIC_METADATA_BLOCK	0x06
>> +#define USE_EXTENDED_TAG		0x07
>>  #define EXT_VIDEO_DATA_BLOCK_420	0x0E
>> -#define EXT_VIDEO_CAP_BLOCK_Y420CMDB 0x0F
>> +#define EXT_VIDEO_CAP_BLOCK_Y420CMDB	0x0F
>> +#define EXT_VIDEO_HF_EEODB_DATA_BLOCK	0x78
>>  #define EDID_BASIC_AUDIO	(1 << 6)
>>  #define EDID_CEA_YCRCB444	(1 << 5)
>>  #define EDID_CEA_YCRCB422	(1 << 4)
>>  #define EDID_CEA_VCDB_QS	(1 << 6)
>> +#define HF_EEODB_LENGTH		2
>>  
>>  /*
>>   * Search EDID for CEA extension block.
>> @@ -4274,9 +4305,41 @@ static bool cea_db_is_y420vdb(const u8 *db)
>>  	return true;
>>  }
>>  
>> +static bool cea_db_is_hdmi_forum_eeodb(const u8 *db) {
>> +	if (cea_db_tag(db) != USE_EXTENDED_TAG)
>> +		return false;
>> +
>> +	if (cea_db_payload_len(db) != HF_EEODB_LENGTH)
>> +		return false;
>> +
>> +	if (cea_db_extended_tag(db) != EXT_VIDEO_HF_EEODB_DATA_BLOCK)
>> +		return false;
>> +
>> +	return true;
>> +}
>> +
>>  #define for_each_cea_db(cea, i, start, end) \
>>  	for ((i) = (start); (i) < (end) && (i) + 
>> cea_db_payload_len(&(cea)[(i)]) < (end); (i) += 
>> cea_db_payload_len(&(cea)[(i)]) + 1)
>>  
>> +size_t drm_edid_read_hf_eeodb_blk_count(const struct edid *edid) {
>> +	const u8 *cea;
>> +	int i, start, end, cea_ext_index = 0, displayid_ext_index = 0;
>> +
>> +	if (edid->extensions) {
>> +		cea = drm_find_cea_extension(edid, &cea_ext_index, 
>> +&displayid_ext_index);
>> +
>> +		if (cea && !cea_db_offsets(cea, &start, &end))
>> +			for_each_cea_db(cea, i, start, end)
>> +				if (cea_db_is_hdmi_forum_eeodb(&cea[i]))
>> +					return cea[i + 2];
>> +	}
>> +
>> +	return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(drm_edid_read_hf_eeodb_blk_count);
>
>This should be static and not exported.
>
>BR,
>Jani.
>
>> +
>>  static void drm_parse_y420cmdb_bitmap(struct drm_connector *connector,
>>  				      const u8 *db)
>>  {
>> diff --git a/include/drm/drm_edid.h b/include/drm/drm_edid.h index 
>> 144c495b99c4..585f0ed932d4 100644
>> --- a/include/drm/drm_edid.h
>> +++ b/include/drm/drm_edid.h
>> @@ -593,5 +593,6 @@ drm_display_mode_from_cea_vic(struct drm_device 
>> *dev,  const u8 *drm_find_edid_extension(const struct edid *edid,
>>  				  int ext_id, int *ext_index);
>>  
>> +size_t drm_edid_read_hf_eeodb_blk_count(const struct edid *edid);
>>  
>>  #endif /* __DRM_EDID_H__ */
>
>--
>Jani Nikula, Intel Open Source Graphics Center
diff mbox series

Patch

diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
index a50c82bc2b2f..16011023c12e 100644
--- a/drivers/gpu/drm/drm_connector.c
+++ b/drivers/gpu/drm/drm_connector.c
@@ -2129,7 +2129,7 @@  int drm_connector_update_edid_property(struct drm_connector *connector,
 				       const struct edid *edid)
 {
 	struct drm_device *dev = connector->dev;
-	size_t size = 0;
+	size_t size = 0, hf_eeodb_blk_count;
 	int ret;
 	const struct edid *old_edid;
 
@@ -2137,8 +2137,12 @@  int drm_connector_update_edid_property(struct drm_connector *connector,
 	if (connector->override_edid)
 		return 0;
 
-	if (edid)
+	if (edid) {
 		size = EDID_LENGTH * (1 + edid->extensions);
+		hf_eeodb_blk_count = drm_edid_read_hf_eeodb_blk_count(edid);
+		if (hf_eeodb_blk_count)
+			size = EDID_LENGTH * (1 + hf_eeodb_blk_count);
+	}
 
 	/* Set the display info, using edid if available, otherwise
 	 * resetting the values to defaults. This duplicates the work
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 9fa84881fbba..5ae4e83fa5e3 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -1992,6 +1992,7 @@  struct edid *drm_do_get_edid(struct drm_connector *connector,
 {
 	int i, j = 0, valid_extensions = 0;
 	u8 *edid, *new;
+	size_t hf_eeodb_blk_count;
 	struct edid *override;
 
 	override = drm_get_override_edid(connector);
@@ -2051,7 +2052,35 @@  struct edid *drm_do_get_edid(struct drm_connector *connector,
 		}
 
 		kfree(edid);
+		return (struct edid *)new;
+	}
+
+	hf_eeodb_blk_count = drm_edid_read_hf_eeodb_blk_count((struct edid *)edid);
+	if (hf_eeodb_blk_count >= 2) {
+		new = krealloc(edid, (hf_eeodb_blk_count + 1) * EDID_LENGTH, GFP_KERNEL);
+		if (!new)
+			goto out;
 		edid = new;
+
+		valid_extensions = hf_eeodb_blk_count - 1;
+		for (j = 2; j <= hf_eeodb_blk_count; j++) {
+			u8 *block = edid + j * EDID_LENGTH;
+
+			for (i = 0; i < 4; i++) {
+				if (get_edid_block(data, block, j, EDID_LENGTH))
+					goto out;
+				if (drm_edid_block_valid(block, j, false, NULL))
+					break;
+			}
+
+			if (i == 4)
+				valid_extensions--;
+		}
+
+		if (valid_extensions != hf_eeodb_blk_count - 1) {
+			DRM_ERROR("Not able to retrieve proper EDID contain HF-EEODB data.\n");
+			goto out;
+		}
 	}
 
 	return (struct edid *)edid;
@@ -3315,15 +3344,17 @@  add_detailed_modes(struct drm_connector *connector, struct edid *edid,
 #define VIDEO_BLOCK     0x02
 #define VENDOR_BLOCK    0x03
 #define SPEAKER_BLOCK	0x04
-#define HDR_STATIC_METADATA_BLOCK	0x6
-#define USE_EXTENDED_TAG 0x07
-#define EXT_VIDEO_CAPABILITY_BLOCK 0x00
+#define EXT_VIDEO_CAPABILITY_BLOCK	0x00
+#define HDR_STATIC_METADATA_BLOCK	0x06
+#define USE_EXTENDED_TAG		0x07
 #define EXT_VIDEO_DATA_BLOCK_420	0x0E
-#define EXT_VIDEO_CAP_BLOCK_Y420CMDB 0x0F
+#define EXT_VIDEO_CAP_BLOCK_Y420CMDB	0x0F
+#define EXT_VIDEO_HF_EEODB_DATA_BLOCK	0x78
 #define EDID_BASIC_AUDIO	(1 << 6)
 #define EDID_CEA_YCRCB444	(1 << 5)
 #define EDID_CEA_YCRCB422	(1 << 4)
 #define EDID_CEA_VCDB_QS	(1 << 6)
+#define HF_EEODB_LENGTH		2
 
 /*
  * Search EDID for CEA extension block.
@@ -4274,9 +4305,41 @@  static bool cea_db_is_y420vdb(const u8 *db)
 	return true;
 }
 
+static bool cea_db_is_hdmi_forum_eeodb(const u8 *db)
+{
+	if (cea_db_tag(db) != USE_EXTENDED_TAG)
+		return false;
+
+	if (cea_db_payload_len(db) != HF_EEODB_LENGTH)
+		return false;
+
+	if (cea_db_extended_tag(db) != EXT_VIDEO_HF_EEODB_DATA_BLOCK)
+		return false;
+
+	return true;
+}
+
 #define for_each_cea_db(cea, i, start, end) \
 	for ((i) = (start); (i) < (end) && (i) + cea_db_payload_len(&(cea)[(i)]) < (end); (i) += cea_db_payload_len(&(cea)[(i)]) + 1)
 
+size_t drm_edid_read_hf_eeodb_blk_count(const struct edid *edid)
+{
+	const u8 *cea;
+	int i, start, end, cea_ext_index = 0, displayid_ext_index = 0;
+
+	if (edid->extensions) {
+		cea = drm_find_cea_extension(edid, &cea_ext_index, &displayid_ext_index);
+
+		if (cea && !cea_db_offsets(cea, &start, &end))
+			for_each_cea_db(cea, i, start, end)
+				if (cea_db_is_hdmi_forum_eeodb(&cea[i]))
+					return cea[i + 2];
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(drm_edid_read_hf_eeodb_blk_count);
+
 static void drm_parse_y420cmdb_bitmap(struct drm_connector *connector,
 				      const u8 *db)
 {
diff --git a/include/drm/drm_edid.h b/include/drm/drm_edid.h
index 144c495b99c4..585f0ed932d4 100644
--- a/include/drm/drm_edid.h
+++ b/include/drm/drm_edid.h
@@ -593,5 +593,6 @@  drm_display_mode_from_cea_vic(struct drm_device *dev,
 const u8 *drm_find_edid_extension(const struct edid *edid,
 				  int ext_id, int *ext_index);
 
+size_t drm_edid_read_hf_eeodb_blk_count(const struct edid *edid);
 
 #endif /* __DRM_EDID_H__ */