[PATCH] drm/bridge: adv7511: fix support for large EDIDs

[PATCH] drm/bridge: adv7511: fix support for large EDIDs

[Hans Verkuil]

While testing support for large (> 256 bytes) EDIDs on the Renesas
Koelsch board I noticed that the adv7511 bridge driver only read the
first two blocks.

The media V4L2 version for the adv7511 (drivers/media/i2c/adv7511-v4l2.c)
handled this correctly.

Besides a simple bug when setting the segment register (it was set to the
block number instead of block / 2), the logic of the code was also weird.
In particular reading the DDC_STATUS is odd: this is unrelated to EDID
reading.

The reworked code just waits for any EDID segment reads to finish (this
does nothing if the a segment is already read), checks if the desired
segment matches the read segment, and if not, then it requests the new
segment and waits again for the EDID segment to be read.

Finally it checks if the currently buffered EDID segment contains the
desired EDID block, and if not it will update the EDID buffer from
the adv7511.

Tested with my Koelsch board and with EDIDs of 1, 2, 3 and 4 blocks.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
---
Testing on the Renesas board also requires these two adv7604 patches
if you want to test with an HDMI cable between the HDMI input and output:

https://patchwork.linuxtv.org/project/linux-media/patch/00882808-472a-d429-c565-a701da579ead@xs4all.nl/
https://patchwork.linuxtv.org/project/linux-media/patch/c7093e76-ffb4-b19c-f576-b264f935a3ce@xs4all.nl/
---
diff --git a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
index 76555ae64e9c..9e8db1c60167 100644
--- a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
+++ b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
@@ -328,6 +328,7 @@ static void adv7511_set_link_config(struct adv7511 *adv7511,
 static void __adv7511_power_on(struct adv7511 *adv7511)
 {
 	adv7511->current_edid_segment = -1;
+	adv7511->edid_read = false;

 	regmap_update_bits(adv7511->regmap, ADV7511_REG_POWER,
 			   ADV7511_POWER_POWER_DOWN, 0);
@@ -529,29 +530,35 @@ static int adv7511_get_edid_block(void *data, u8 *buf, unsigned int block,
 	struct adv7511 *adv7511 = data;
 	struct i2c_msg xfer[2];
 	uint8_t offset;
+	unsigned int cur_segment;
 	unsigned int i;
 	int ret;

 	if (len > 128)
 		return -EINVAL;

-	if (adv7511->current_edid_segment != block / 2) {
-		unsigned int status;
+	/* wait for any EDID segment reads to finish */
+	adv7511_wait_for_edid(adv7511, 200);

-		ret = regmap_read(adv7511->regmap, ADV7511_REG_DDC_STATUS,
-				  &status);
+	ret = regmap_read(adv7511->regmap, ADV7511_REG_EDID_SEGMENT, &cur_segment);
+	if (ret < 0)
+		return ret;
+
+	/*
+	 * If the current read segment does not match what we need, then
+	 * write the new segment and wait for it to be read.
+	 */
+	if (cur_segment != block / 2) {
+		adv7511->edid_read = false;
+		cur_segment = block / 2;
+		regmap_write(adv7511->regmap, ADV7511_REG_EDID_SEGMENT,
+			     cur_segment);
+		ret = adv7511_wait_for_edid(adv7511, 200);
 		if (ret < 0)
 			return ret;
+	}

-		if (status != 2) {
-			adv7511->edid_read = false;
-			regmap_write(adv7511->regmap, ADV7511_REG_EDID_SEGMENT,
-				     block);
-			ret = adv7511_wait_for_edid(adv7511, 200);
-			if (ret < 0)
-				return ret;
-		}
-
+	if (adv7511->current_edid_segment != cur_segment) {
 		/* Break this apart, hopefully more I2C controllers will
 		 * support 64 byte transfers than 256 byte transfers
 		 */
@@ -579,7 +586,7 @@ static int adv7511_get_edid_block(void *data, u8 *buf, unsigned int block,
 			offset += 64;
 		}

-		adv7511->current_edid_segment = block / 2;
+		adv7511->current_edid_segment = cur_segment;
 	}

 	if (block % 2 == 0)

Re: [PATCH] drm/bridge: adv7511: fix support for large EDIDs

[Niklas Söderlund]

Hi Hans,

Thanks for your patch.

On 2021-03-24 09:53:32 +0100, Hans Verkuil wrote:
> While testing support for large (> 256 bytes) EDIDs on the Renesas
> Koelsch board I noticed that the adv7511 bridge driver only read the
> first two blocks.
> 
> The media V4L2 version for the adv7511 (drivers/media/i2c/adv7511-v4l2.c)
> handled this correctly.
> 
> Besides a simple bug when setting the segment register (it was set to the
> block number instead of block / 2), the logic of the code was also weird.
> In particular reading the DDC_STATUS is odd: this is unrelated to EDID
> reading.
> 
> The reworked code just waits for any EDID segment reads to finish (this
> does nothing if the a segment is already read), checks if the desired
> segment matches the read segment, and if not, then it requests the new
> segment and waits again for the EDID segment to be read.
> 
> Finally it checks if the currently buffered EDID segment contains the
> desired EDID block, and if not it will update the EDID buffer from
> the adv7511.
> 
> Tested with my Koelsch board and with EDIDs of 1, 2, 3 and 4 blocks.
> 
> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>

Tested-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>

> ---
> Testing on the Renesas board also requires these two adv7604 patches
> if you want to test with an HDMI cable between the HDMI input and output:
> 
> https://patchwork.linuxtv.org/project/linux-media/patch/00882808-472a-d429-c565-a701da579ead@xs4all.nl/
> https://patchwork.linuxtv.org/project/linux-media/patch/c7093e76-ffb4-b19c-f576-b264f935a3ce@xs4all.nl/
> ---
> diff --git a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> index 76555ae64e9c..9e8db1c60167 100644
> --- a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> +++ b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> @@ -328,6 +328,7 @@ static void adv7511_set_link_config(struct adv7511 *adv7511,
>  static void __adv7511_power_on(struct adv7511 *adv7511)
>  {
>  	adv7511->current_edid_segment = -1;
> +	adv7511->edid_read = false;
> 
>  	regmap_update_bits(adv7511->regmap, ADV7511_REG_POWER,
>  			   ADV7511_POWER_POWER_DOWN, 0);
> @@ -529,29 +530,35 @@ static int adv7511_get_edid_block(void *data, u8 *buf, unsigned int block,
>  	struct adv7511 *adv7511 = data;
>  	struct i2c_msg xfer[2];
>  	uint8_t offset;
> +	unsigned int cur_segment;
>  	unsigned int i;
>  	int ret;
> 
>  	if (len > 128)
>  		return -EINVAL;
> 
> -	if (adv7511->current_edid_segment != block / 2) {
> -		unsigned int status;
> +	/* wait for any EDID segment reads to finish */
> +	adv7511_wait_for_edid(adv7511, 200);
> 
> -		ret = regmap_read(adv7511->regmap, ADV7511_REG_DDC_STATUS,
> -				  &status);
> +	ret = regmap_read(adv7511->regmap, ADV7511_REG_EDID_SEGMENT, &cur_segment);
> +	if (ret < 0)
> +		return ret;
> +
> +	/*
> +	 * If the current read segment does not match what we need, then
> +	 * write the new segment and wait for it to be read.
> +	 */
> +	if (cur_segment != block / 2) {
> +		adv7511->edid_read = false;
> +		cur_segment = block / 2;
> +		regmap_write(adv7511->regmap, ADV7511_REG_EDID_SEGMENT,
> +			     cur_segment);
> +		ret = adv7511_wait_for_edid(adv7511, 200);
>  		if (ret < 0)
>  			return ret;
> +	}
> 
> -		if (status != 2) {
> -			adv7511->edid_read = false;
> -			regmap_write(adv7511->regmap, ADV7511_REG_EDID_SEGMENT,
> -				     block);
> -			ret = adv7511_wait_for_edid(adv7511, 200);
> -			if (ret < 0)
> -				return ret;
> -		}
> -
> +	if (adv7511->current_edid_segment != cur_segment) {
>  		/* Break this apart, hopefully more I2C controllers will
>  		 * support 64 byte transfers than 256 byte transfers
>  		 */
> @@ -579,7 +586,7 @@ static int adv7511_get_edid_block(void *data, u8 *buf, unsigned int block,
>  			offset += 64;
>  		}
> 
> -		adv7511->current_edid_segment = block / 2;
> +		adv7511->current_edid_segment = cur_segment;
>  	}
> 
>  	if (block % 2 == 0)

-- 
Regards,
Niklas Söderlund

Re: [PATCH] drm/bridge: adv7511: fix support for large EDIDs

[Laurent Pinchart]

Hi Hans,

Thank you for the patch.

On Wed, Mar 24, 2021 at 09:53:32AM +0100, Hans Verkuil wrote:
> While testing support for large (> 256 bytes) EDIDs on the Renesas
> Koelsch board I noticed that the adv7511 bridge driver only read the
> first two blocks.
> 
> The media V4L2 version for the adv7511 (drivers/media/i2c/adv7511-v4l2.c)
> handled this correctly.
> 
> Besides a simple bug when setting the segment register (it was set to the
> block number instead of block / 2), the logic of the code was also weird.
> In particular reading the DDC_STATUS is odd: this is unrelated to EDID
> reading.

Bits 3:0 of DDC_STATUS report the DDC controller state, which can be
used to wait until the DDC controller is idle (it reports, among other
possible states, if an EDID read is in progress). Other options are
possible of course, including waiting for ADV7511_INT0_EDID_READY as
done in adv7511_wait_for_edid(), but I wonder if the !irq case in
adv7511_wait_for_edid() wouldn't be better of busy-looping on the DDC
status instead of running the interrupt handler manually. That's
unrelated to this patch though.

> The reworked code just waits for any EDID segment reads to finish (this
> does nothing if the a segment is already read), checks if the desired
> segment matches the read segment, and if not, then it requests the new
> segment and waits again for the EDID segment to be read.
> 
> Finally it checks if the currently buffered EDID segment contains the
> desired EDID block, and if not it will update the EDID buffer from
> the adv7511.
> 
> Tested with my Koelsch board and with EDIDs of 1, 2, 3 and 4 blocks.
> 
> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
> ---
> Testing on the Renesas board also requires these two adv7604 patches
> if you want to test with an HDMI cable between the HDMI input and output:
> 
> https://patchwork.linuxtv.org/project/linux-media/patch/00882808-472a-d429-c565-a701da579ead@xs4all.nl/
> https://patchwork.linuxtv.org/project/linux-media/patch/c7093e76-ffb4-b19c-f576-b264f935a3ce@xs4all.nl/
> ---
> diff --git a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> index 76555ae64e9c..9e8db1c60167 100644
> --- a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> +++ b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> @@ -328,6 +328,7 @@ static void adv7511_set_link_config(struct adv7511 *adv7511,
>  static void __adv7511_power_on(struct adv7511 *adv7511)
>  {
>  	adv7511->current_edid_segment = -1;
> +	adv7511->edid_read = false;
> 
>  	regmap_update_bits(adv7511->regmap, ADV7511_REG_POWER,
>  			   ADV7511_POWER_POWER_DOWN, 0);
> @@ -529,29 +530,35 @@ static int adv7511_get_edid_block(void *data, u8 *buf, unsigned int block,
>  	struct adv7511 *adv7511 = data;
>  	struct i2c_msg xfer[2];
>  	uint8_t offset;
> +	unsigned int cur_segment;
>  	unsigned int i;
>  	int ret;
> 
>  	if (len > 128)
>  		return -EINVAL;
> 
> -	if (adv7511->current_edid_segment != block / 2) {
> -		unsigned int status;
> +	/* wait for any EDID segment reads to finish */
> +	adv7511_wait_for_edid(adv7511, 200);

Why do we need to wait for the EDID read to complete here ? Does the
ADV7511 initiate an EDID read by itself that we need to wait for it to
complete ?

> 
> -		ret = regmap_read(adv7511->regmap, ADV7511_REG_DDC_STATUS,
> -				  &status);
> +	ret = regmap_read(adv7511->regmap, ADV7511_REG_EDID_SEGMENT, &cur_segment);
> +	if (ret < 0)
> +		return ret;

Do we need to read this from the device, can't we instead use
current_edid_segment ?

> +
> +	/*
> +	 * If the current read segment does not match what we need, then
> +	 * write the new segment and wait for it to be read.
> +	 */
> +	if (cur_segment != block / 2) {
> +		adv7511->edid_read = false;
> +		cur_segment = block / 2;
> +		regmap_write(adv7511->regmap, ADV7511_REG_EDID_SEGMENT,
> +			     cur_segment);
> +		ret = adv7511_wait_for_edid(adv7511, 200);
>  		if (ret < 0)
>  			return ret;
> +	}
> 
> -		if (status != 2) {
> -			adv7511->edid_read = false;
> -			regmap_write(adv7511->regmap, ADV7511_REG_EDID_SEGMENT,
> -				     block);
> -			ret = adv7511_wait_for_edid(adv7511, 200);
> -			if (ret < 0)
> -				return ret;
> -		}
> -
> +	if (adv7511->current_edid_segment != cur_segment) {

Do you need to test this condition separately from the previous one ?

>  		/* Break this apart, hopefully more I2C controllers will
>  		 * support 64 byte transfers than 256 byte transfers
>  		 */
> @@ -579,7 +586,7 @@ static int adv7511_get_edid_block(void *data, u8 *buf, unsigned int block,
>  			offset += 64;
>  		}
> 
> -		adv7511->current_edid_segment = block / 2;
> +		adv7511->current_edid_segment = cur_segment;
>  	}
> 
>  	if (block % 2 == 0)

-- 
Regards,

Laurent Pinchart

Re: [PATCH] drm/bridge: adv7511: fix support for large EDIDs

[Hans Verkuil]

Hi Laurent,

Thank you for the review.

On 26/03/2021 02:00, Laurent Pinchart wrote:
> Hi Hans,
> 
> Thank you for the patch.
> 
> On Wed, Mar 24, 2021 at 09:53:32AM +0100, Hans Verkuil wrote:
>> While testing support for large (> 256 bytes) EDIDs on the Renesas
>> Koelsch board I noticed that the adv7511 bridge driver only read the
>> first two blocks.
>>
>> The media V4L2 version for the adv7511 (drivers/media/i2c/adv7511-v4l2.c)
>> handled this correctly.
>>
>> Besides a simple bug when setting the segment register (it was set to the
>> block number instead of block / 2), the logic of the code was also weird.
>> In particular reading the DDC_STATUS is odd: this is unrelated to EDID
>> reading.
> 
> Bits 3:0 of DDC_STATUS report the DDC controller state, which can be
> used to wait until the DDC controller is idle (it reports, among other
> possible states, if an EDID read is in progress). Other options are
> possible of course, including waiting for ADV7511_INT0_EDID_READY as
> done in adv7511_wait_for_edid(), but I wonder if the !irq case in
> adv7511_wait_for_edid() wouldn't be better of busy-looping on the DDC
> status instead of running the interrupt handler manually. That's
> unrelated to this patch though.
> 
>> The reworked code just waits for any EDID segment reads to finish (this
>> does nothing if the a segment is already read), checks if the desired
>> segment matches the read segment, and if not, then it requests the new
>> segment and waits again for the EDID segment to be read.
>>
>> Finally it checks if the currently buffered EDID segment contains the
>> desired EDID block, and if not it will update the EDID buffer from
>> the adv7511.
>>
>> Tested with my Koelsch board and with EDIDs of 1, 2, 3 and 4 blocks.
>>
>> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
>> ---
>> Testing on the Renesas board also requires these two adv7604 patches
>> if you want to test with an HDMI cable between the HDMI input and output:
>>
>> https://patchwork.linuxtv.org/project/linux-media/patch/00882808-472a-d429-c565-a701da579ead@xs4all.nl/
>> https://patchwork.linuxtv.org/project/linux-media/patch/c7093e76-ffb4-b19c-f576-b264f935a3ce@xs4all.nl/
>> ---
>> diff --git a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
>> index 76555ae64e9c..9e8db1c60167 100644
>> --- a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
>> +++ b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
>> @@ -328,6 +328,7 @@ static void adv7511_set_link_config(struct adv7511 *adv7511,
>>  static void __adv7511_power_on(struct adv7511 *adv7511)
>>  {
>>  	adv7511->current_edid_segment = -1;
>> +	adv7511->edid_read = false;
>>
>>  	regmap_update_bits(adv7511->regmap, ADV7511_REG_POWER,
>>  			   ADV7511_POWER_POWER_DOWN, 0);
>> @@ -529,29 +530,35 @@ static int adv7511_get_edid_block(void *data, u8 *buf, unsigned int block,
>>  	struct adv7511 *adv7511 = data;
>>  	struct i2c_msg xfer[2];
>>  	uint8_t offset;
>> +	unsigned int cur_segment;
>>  	unsigned int i;
>>  	int ret;
>>
>>  	if (len > 128)
>>  		return -EINVAL;
>>
>> -	if (adv7511->current_edid_segment != block / 2) {
>> -		unsigned int status;
>> +	/* wait for any EDID segment reads to finish */
>> +	adv7511_wait_for_edid(adv7511, 200);
> 
> Why do we need to wait for the EDID read to complete here ? Does the
> ADV7511 initiate an EDID read by itself that we need to wait for it to
> complete ?

Yes. When powered on it will automatically start to read the first segment.

> 
>>
>> -		ret = regmap_read(adv7511->regmap, ADV7511_REG_DDC_STATUS,
>> -				  &status);
>> +	ret = regmap_read(adv7511->regmap, ADV7511_REG_EDID_SEGMENT, &cur_segment);
>> +	if (ret < 0)
>> +		return ret;
> 
> Do we need to read this from the device, can't we instead use
> current_edid_segment ?

We can, provided we take into account that after poweron current_edid_segment is -1,
and in that case we must not set ADV7511_REG_EDID_SEGMENT again.

I'll make that change.

> 
>> +
>> +	/*
>> +	 * If the current read segment does not match what we need, then
>> +	 * write the new segment and wait for it to be read.
>> +	 */
>> +	if (cur_segment != block / 2) {
>> +		adv7511->edid_read = false;
>> +		cur_segment = block / 2;
>> +		regmap_write(adv7511->regmap, ADV7511_REG_EDID_SEGMENT,
>> +			     cur_segment);
>> +		ret = adv7511_wait_for_edid(adv7511, 200);
>>  		if (ret < 0)
>>  			return ret;
>> +	}
>>
>> -		if (status != 2) {
>> -			adv7511->edid_read = false;
>> -			regmap_write(adv7511->regmap, ADV7511_REG_EDID_SEGMENT,
>> -				     block);
>> -			ret = adv7511_wait_for_edid(adv7511, 200);
>> -			if (ret < 0)
>> -				return ret;
>> -		}
>> -
>> +	if (adv7511->current_edid_segment != cur_segment) {
> 
> Do you need to test this condition separately from the previous one ?

Yes, again for the initial power on case where segment 0 has been read
without ADV7511_REG_EDID_SEGMENT being written by us, and so we still
need to read out segment 0 from the adv7511.

I'll add some comments in v2.

> 
>>  		/* Break this apart, hopefully more I2C controllers will
>>  		 * support 64 byte transfers than 256 byte transfers
>>  		 */
>> @@ -579,7 +586,7 @@ static int adv7511_get_edid_block(void *data, u8 *buf, unsigned int block,
>>  			offset += 64;
>>  		}
>>
>> -		adv7511->current_edid_segment = block / 2;
>> +		adv7511->current_edid_segment = cur_segment;
>>  	}
>>
>>  	if (block % 2 == 0)
> 

Regards,

	Hans

Re: [PATCH] drm/bridge: adv7511: fix support for large EDIDs

[Hans Verkuil]

On 26/03/2021 02:00, Laurent Pinchart wrote:
> Hi Hans,
> 
> Thank you for the patch.
> 
> On Wed, Mar 24, 2021 at 09:53:32AM +0100, Hans Verkuil wrote:
>> While testing support for large (> 256 bytes) EDIDs on the Renesas
>> Koelsch board I noticed that the adv7511 bridge driver only read the
>> first two blocks.
>>
>> The media V4L2 version for the adv7511 (drivers/media/i2c/adv7511-v4l2.c)
>> handled this correctly.
>>
>> Besides a simple bug when setting the segment register (it was set to the
>> block number instead of block / 2), the logic of the code was also weird.
>> In particular reading the DDC_STATUS is odd: this is unrelated to EDID
>> reading.
> 
> Bits 3:0 of DDC_STATUS report the DDC controller state, which can be
> used to wait until the DDC controller is idle (it reports, among other
> possible states, if an EDID read is in progress). Other options are
> possible of course, including waiting for ADV7511_INT0_EDID_READY as
> done in adv7511_wait_for_edid(), but I wonder if the !irq case in
> adv7511_wait_for_edid() wouldn't be better of busy-looping on the DDC
> status instead of running the interrupt handler manually. That's
> unrelated to this patch though.

The DDC status tests for other things as well, including HDCP.

I think it is pure luck that this code even worked:

        if (adv7511->current_edid_segment != block / 2) {
                unsigned int status;

                ret = regmap_read(adv7511->regmap, ADV7511_REG_DDC_STATUS,
                                  &status);
                if (ret < 0)
                        return ret;

                if (status != 2) {
                        adv7511->edid_read = false;
                        regmap_write(adv7511->regmap, ADV7511_REG_EDID_SEGMENT,
                                     block);
                        ret = adv7511_wait_for_edid(adv7511, 200);
                        if (ret < 0)
                                return ret;
                }

What happens on power on is that the adv7511 starts reading the EDID.
So the DDC_STATUS is 1 (Reading EDID). This code is called, it falls
in the status != 2 block, it writes the EDID_SEGMENT with 0 (it already
is 0 after a power on), then waits for the EDID read to finish.

The only reason this works is that this code is called fast enough
after the device is powered on that it is still reading the EDID.

It fails if you want to read the next segment, since in that case the
status is 2 (IDLE) and it will never write the new segment to the
EDID_SEGMENT register.

And besides, status wasn't ANDed with 0xf either, and HDCP might
also be ongoing (should that be enabled in the future).

Regards,

	Hans

Re: [PATCH] drm/bridge: adv7511: fix support for large EDIDs

[Laurent Pinchart]

Hi Hans,

On Fri, Mar 26, 2021 at 07:31:09AM +0100, Hans Verkuil wrote:
> On 26/03/2021 02:00, Laurent Pinchart wrote:
> > On Wed, Mar 24, 2021 at 09:53:32AM +0100, Hans Verkuil wrote:
> >> While testing support for large (> 256 bytes) EDIDs on the Renesas
> >> Koelsch board I noticed that the adv7511 bridge driver only read the
> >> first two blocks.
> >>
> >> The media V4L2 version for the adv7511 (drivers/media/i2c/adv7511-v4l2.c)
> >> handled this correctly.
> >>
> >> Besides a simple bug when setting the segment register (it was set to the
> >> block number instead of block / 2), the logic of the code was also weird.
> >> In particular reading the DDC_STATUS is odd: this is unrelated to EDID
> >> reading.
> > 
> > Bits 3:0 of DDC_STATUS report the DDC controller state, which can be
> > used to wait until the DDC controller is idle (it reports, among other
> > possible states, if an EDID read is in progress). Other options are
> > possible of course, including waiting for ADV7511_INT0_EDID_READY as
> > done in adv7511_wait_for_edid(), but I wonder if the !irq case in
> > adv7511_wait_for_edid() wouldn't be better of busy-looping on the DDC
> > status instead of running the interrupt handler manually. That's
> > unrelated to this patch though.
> 
> The DDC status tests for other things as well, including HDCP.

I haven't read the chip's documentation in details, but if HDCP
negotiation is in progress, doesn't that keep the DDC bus busy,
preventing an EDID read ?

> I think it is pure luck that this code even worked:
> 
>         if (adv7511->current_edid_segment != block / 2) {
>                 unsigned int status;
> 
>                 ret = regmap_read(adv7511->regmap, ADV7511_REG_DDC_STATUS,
>                                   &status);
>                 if (ret < 0)
>                         return ret;
> 
>                 if (status != 2) {
>                         adv7511->edid_read = false;
>                         regmap_write(adv7511->regmap, ADV7511_REG_EDID_SEGMENT,
>                                      block);
>                         ret = adv7511_wait_for_edid(adv7511, 200);
>                         if (ret < 0)
>                                 return ret;
>                 }
> 
> What happens on power on is that the adv7511 starts reading the EDID.
> So the DDC_STATUS is 1 (Reading EDID). This code is called, it falls
> in the status != 2 block, it writes the EDID_SEGMENT with 0 (it already
> is 0 after a power on), then waits for the EDID read to finish.
> 
> The only reason this works is that this code is called fast enough
> after the device is powered on that it is still reading the EDID.

Yes, I agree with you. Luck is nice, except when it makes us merge
incorrect code :-)

> It fails if you want to read the next segment, since in that case the
> status is 2 (IDLE) and it will never write the new segment to the
> EDID_SEGMENT register.
> 
> And besides, status wasn't ANDed with 0xf either, and HDCP might
> also be ongoing (should that be enabled in the future).

-- 
Regards,

Laurent Pinchart