Re: [PATCH] drm/bridge: lt9611uxc: Increase EDID_NUM_BLOCKS from 2 to 4 for extended EDID support

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

On Mon, 02 Feb 2026, Nilesh Laad <nilesh.laad@oss.qualcomm.com> wrote:
> From: Ravi Agola <raviagol@qti.qualcomm.com>
>
> The lt9611uxc driver previously limited EDID reading to 2 blocks, which
> restricted support for displays that provide more than two EDID blocks.
> This change enables the driver to read and pass up to 4 EDID blocks from
> the LT9611UXC to drm_edid calls.
> As a result, the driver now supports displays with up to 4 EDID block.
>
> Signed-off-by: Ravi Agola <raviagol@qti.qualcomm.com>
> Signed-off-by: Nilesh Laad <nilesh.laad@oss.qualcomm.com>
> ---
>  drivers/gpu/drm/bridge/lontium-lt9611uxc.c | 93 ++++++++++++++++++++++++++----
>  1 file changed, 82 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/lontium-lt9611uxc.c b/drivers/gpu/drm/bridge/lontium-lt9611uxc.c
> index 4d989381904c..7fe481c7acf8 100644
> --- a/drivers/gpu/drm/bridge/lontium-lt9611uxc.c
> +++ b/drivers/gpu/drm/bridge/lontium-lt9611uxc.c
> @@ -28,7 +28,7 @@
>  #include <drm/display/drm_hdmi_audio_helper.h>
>  
>  #define EDID_BLOCK_SIZE	128
> -#define EDID_NUM_BLOCKS	2
> +#define EDID_NUM_BLOCKS	4
>  
>  #define FW_FILE "lt9611uxc_fw.bin"
>  
> @@ -61,6 +61,11 @@ struct lt9611uxc {
>  	/* can be accessed from different threads, so protect this with ocm_lock */
>  	bool hdmi_connected;
>  	uint8_t fw_version;
> +
> +	bool edid_available;
> +	unsigned int num_edid_blocks;
> +	uint8_t edid_raw[EDID_BLOCK_SIZE * EDID_NUM_BLOCKS];
> +
>  };
>  
>  #define LT9611_PAGE_CONTROL	0xff
> @@ -170,8 +175,12 @@ static void lt9611uxc_hpd_work(struct work_struct *work)
>  	connected = lt9611uxc->hdmi_connected;
>  	mutex_unlock(&lt9611uxc->ocm_lock);
>  
> -	if (!connected)
> +	if (!connected) {
>  		lt9611uxc->edid_read = false;
> +		lt9611uxc->edid_available = false;
> +		lt9611uxc->num_edid_blocks = 0;
> +		memset(lt9611uxc->edid_raw, 0, EDID_BLOCK_SIZE * EDID_NUM_BLOCKS);
> +	}
>  
>  	drm_bridge_hpd_notify(&lt9611uxc->bridge,
>  			      connected ?
> @@ -387,10 +396,32 @@ static int lt9611uxc_wait_for_edid(struct lt9611uxc *lt9611uxc)
>  			msecs_to_jiffies(500));
>  }
>  
> +static int lt9611uxc_read_edid_block(struct lt9611uxc *lt9611uxc, unsigned int block)
> +{
> +	int ret;
> +
> +	lt9611uxc_lock(lt9611uxc);
> +
> +	regmap_write(lt9611uxc->regmap, 0xb00a, (block%2) * EDID_BLOCK_SIZE);
> +
> +	ret = regmap_noinc_read(lt9611uxc->regmap, 0xb0b0,
> +			&lt9611uxc->edid_raw[block*EDID_BLOCK_SIZE], EDID_BLOCK_SIZE);
> +	if (ret) {
> +		dev_err(lt9611uxc->dev, "edid block %d read failed: %d\n", block, ret);
> +		lt9611uxc_unlock(lt9611uxc);
> +		return -EINVAL;
> +	}
> +	lt9611uxc_unlock(lt9611uxc);
> +
> +	return ret;
> +}
> +
>  static int lt9611uxc_get_edid_block(void *data, u8 *buf, unsigned int block, size_t len)
>  {
>  	struct lt9611uxc *lt9611uxc = data;
> -	int ret;
> +	int ret = 0;
> +	int retry_cnt = 10;
> +	int edid_ext_block;
>  
>  	if (len > EDID_BLOCK_SIZE)
>  		return -EINVAL;
> @@ -398,19 +429,59 @@ static int lt9611uxc_get_edid_block(void *data, u8 *buf, unsigned int block, siz
>  	if (block >= EDID_NUM_BLOCKS)
>  		return -EINVAL;
>  
> -	lt9611uxc_lock(lt9611uxc);
> +	/*
> +	 * if edid is read once, provide same edid data till next hpd event
> +	 */

If you want caching, you should cache the result of
drm_edid_read_custom() at lt9611uxc_bridge_edid_read(). I don't see the
point of having a separate array for this.

Please just try to provide a mechanism to read one block for
drm_edid_read_custom() instead of adding completely separate logic and
then memcpying that.

> +	if (lt9611uxc->edid_available && (block < lt9611uxc->num_edid_blocks))
> +		memcpy(buf, &lt9611uxc->edid_raw[EDID_BLOCK_SIZE*block], EDID_BLOCK_SIZE);

While it is true that drm_edid.c *currently* only passes EDID_BLOCK_SIZE
for len, it's bad form to not respect the passed in len parameter.

BR,
Jani.

> +	else {
> +		/*
> +		 * read number of block available in edid data
> +		 */
> +		if (block == 0) {
> +			lt9611uxc_lock(lt9611uxc);
> +			ret = regmap_read(lt9611uxc->regmap, 0xb02a, &edid_ext_block);
> +			if (ret)
> +				dev_err(lt9611uxc->dev, "edid block read failed: %d\n", ret);
> +			else
> +				lt9611uxc->num_edid_blocks = edid_ext_block & 0x7;
> +			lt9611uxc_unlock(lt9611uxc);
> +		}
>  
> -	regmap_write(lt9611uxc->regmap, 0xb00b, 0x10);
> +		/* read edid block */
> +		ret = lt9611uxc_read_edid_block(lt9611uxc, block);
> +
> +		/* compare first 4 bytes of 0th and 2nd block to confirm
> +		 * that 2nd edid block data is read successfully by lt9611uxc
> +		 */
> +		while ((block == 2) && 0 == memcmp(&lt9611uxc->edid_raw[block*EDID_BLOCK_SIZE],
> +				&lt9611uxc->edid_raw[(block%2)*EDID_BLOCK_SIZE], 4)
> +						&& retry_cnt-- > 0) {
> +			msleep(100);
> +			ret = lt9611uxc_read_edid_block(lt9611uxc, block);
> +		}
>  
> -	regmap_write(lt9611uxc->regmap, 0xb00a, block * EDID_BLOCK_SIZE);
> +		/* if more than 2 edid block are available, reset edid ready
> +		 * flag once 0th and 1st edid block read is completed
> +		 * so lt9611uxc read 2nd and 3rd block
> +		 */
> +		if (block == 1 && lt9611uxc->num_edid_blocks > 2) {
> +			lt9611uxc_lock(lt9611uxc);
> +			regmap_write(lt9611uxc->regmap, 0xb02a, (edid_ext_block & (~BIT(3))));
> +			lt9611uxc_unlock(lt9611uxc);
> +			msleep(100);
> +		}
>  
> -	ret = regmap_noinc_read(lt9611uxc->regmap, 0xb0b0, buf, len);
> -	if (ret)
> -		dev_err(lt9611uxc->dev, "edid read failed: %d\n", ret);
> +		/* set edid available to true once all edid blocks read successfully */
> +		if (block == (lt9611uxc->num_edid_blocks-1) && ret == 0)
> +			lt9611uxc->edid_available = true;
>  
> -	lt9611uxc_unlock(lt9611uxc);
> +		/* copy edid block data into buffer */
> +		if (ret == 0)
> +			memcpy(buf, &lt9611uxc->edid_raw[EDID_BLOCK_SIZE*block], EDID_BLOCK_SIZE);
> +	}
>  
> -	return 0;
> +	return ret;
>  };
>  
>  static const struct drm_edid *lt9611uxc_bridge_edid_read(struct drm_bridge *bridge,
>
> ---
> base-commit: 3ea699b56d31c2a5140d9fac309ff5e0f2041411
> change-id: 20260202-extend-edid-support-b5a4f76d1832
> prerequisite-message-id: 20260202-lt9611uxc-reset-edid-v2-1-b1e1d72edc90@oss.qualcomm.com
> prerequisite-patch-id: bbe63ef7dc85903a286cefd9aa09f1e2e96351b1
>
> Best regards,
> --  
> Nilesh Laad <nilesh.laad@oss.qualcomm.com>
>

-- 
Jani Nikula, Intel