[PATCH] drm/bridge: sii902x: Retry status read after DDI I2C

[PATCH] drm/bridge: sii902x: Retry status read after DDI I2C

[Linus Walleij]

The following happens when connection a DVI output driven
from the SiI9022 using a DVI-to-VGA adapter plug:

i2c i2c-0: sendbytes: NAK bailout.
i2c i2c-0: sendbytes: NAK bailout.

Then no picture. Apparently the I2C engine inside the SiI9022
is not smart enough to try to fall back to DDC I2C. Or the
vendor have not integrated the electronics properly. I don't
know which one it is.

After this, the I2C bus seems stalled and the first attempt to
read the status register fails, and the code returns with
negative return value, and the display fails to initialized.

Instead, retry status readout five times and continue even
if this fails.

Tested on the ARM Versatile Express with a DVI-to-VGA
connector, it now gives picture.

Introduce a helper struct device *dev variable to make
the code more readable.

Cc: Ville Syrj?l? <ville.syrjala@linux.intel.com>
Cc: Liviu Dudau <Liviu.Dudau@arm.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
ChangeLog v1->v2:
- Found the real problem instead of trying to explicitly
  shoehorn EDID modes into the error path.
---
 drivers/gpu/drm/bridge/sii902x.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/bridge/sii902x.c b/drivers/gpu/drm/bridge/sii902x.c
index b1ab4ab09532..60373d7eb220 100644
--- a/drivers/gpu/drm/bridge/sii902x.c
+++ b/drivers/gpu/drm/bridge/sii902x.c
@@ -137,7 +137,9 @@ static int sii902x_get_modes(struct drm_connector *connector)
 	struct sii902x *sii902x = connector_to_sii902x(connector);
 	struct regmap *regmap = sii902x->regmap;
 	u32 bus_format = MEDIA_BUS_FMT_RGB888_1X24;
+	struct device *dev = &sii902x->i2c->dev;
 	unsigned long timeout;
+	unsigned int retries;
 	unsigned int status;
 	struct edid *edid;
 	int num = 0;
@@ -159,7 +161,7 @@ static int sii902x_get_modes(struct drm_connector *connector)
 		 time_before(jiffies, timeout));
 
 	if (!(status & SII902X_SYS_CTRL_DDC_BUS_GRTD)) {
-		dev_err(&sii902x->i2c->dev, "failed to acquire the i2c bus\n");
+		dev_err(dev, "failed to acquire the i2c bus\n");
 		return -ETIMEDOUT;
 	}
 
@@ -179,9 +181,19 @@ static int sii902x_get_modes(struct drm_connector *connector)
 	if (ret)
 		return ret;
 
-	ret = regmap_read(regmap, SII902X_SYS_CTRL_DATA, &status);
+	/*
+	 * Sometimes the I2C bus can stall after failure to use the
+	 * EDID channel. Retry a few times to see if things clear
+	 * up, else continue anyway.
+	 */
+	retries = 5;
+	do {
+		ret = regmap_read(regmap, SII902X_SYS_CTRL_DATA,
+				  &status);
+		retries--;
+	} while (ret && retries);
 	if (ret)
-		return ret;
+		dev_err(dev, "failed to read status (%d)\n", ret);
 
 	ret = regmap_update_bits(regmap, SII902X_SYS_CTRL_DATA,
 				 SII902X_SYS_CTRL_DDC_BUS_REQ |
@@ -201,7 +213,7 @@ static int sii902x_get_modes(struct drm_connector *connector)
 
 	if (status & (SII902X_SYS_CTRL_DDC_BUS_REQ |
 		      SII902X_SYS_CTRL_DDC_BUS_GRTD)) {
-		dev_err(&sii902x->i2c->dev, "failed to release the i2c bus\n");
+		dev_err(dev, "failed to release the i2c bus\n");
 		return -ETIMEDOUT;
 	}
 
-- 
2.14.3

[PATCH] drm/bridge: sii902x: Retry status read after DDI I2C

[Liviu Dudau]

On Mon, Mar 05, 2018 at 11:17:02AM +0100, Linus Walleij wrote:
> The following happens when connection a DVI output driven
> from the SiI9022 using a DVI-to-VGA adapter plug:
> 
> i2c i2c-0: sendbytes: NAK bailout.
> i2c i2c-0: sendbytes: NAK bailout.
> 
> Then no picture. Apparently the I2C engine inside the SiI9022
> is not smart enough to try to fall back to DDC I2C. Or the
> vendor have not integrated the electronics properly. I don't
> know which one it is.
> 
> After this, the I2C bus seems stalled and the first attempt to
> read the status register fails, and the code returns with
> negative return value, and the display fails to initialized.
> 
> Instead, retry status readout five times and continue even
> if this fails.
> 
> Tested on the ARM Versatile Express with a DVI-to-VGA
> connector, it now gives picture.
> 
> Introduce a helper struct device *dev variable to make
> the code more readable.
> 
> Cc: Ville Syrj?l? <ville.syrjala@linux.intel.com>
> Cc: Liviu Dudau <Liviu.Dudau@arm.com>

I don't have a suitable configuration to test this, but looks goot to me.

Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>

BTW, Linus, could it be that your DVI-to-VGA connector doesn't wire
correctly the EDID pin?

Best regards,
Liviu

> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
> ---
> ChangeLog v1->v2:
> - Found the real problem instead of trying to explicitly
>   shoehorn EDID modes into the error path.
> ---
>  drivers/gpu/drm/bridge/sii902x.c | 20 ++++++++++++++++----
>  1 file changed, 16 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/sii902x.c b/drivers/gpu/drm/bridge/sii902x.c
> index b1ab4ab09532..60373d7eb220 100644
> --- a/drivers/gpu/drm/bridge/sii902x.c
> +++ b/drivers/gpu/drm/bridge/sii902x.c
> @@ -137,7 +137,9 @@ static int sii902x_get_modes(struct drm_connector *connector)
>  	struct sii902x *sii902x = connector_to_sii902x(connector);
>  	struct regmap *regmap = sii902x->regmap;
>  	u32 bus_format = MEDIA_BUS_FMT_RGB888_1X24;
> +	struct device *dev = &sii902x->i2c->dev;
>  	unsigned long timeout;
> +	unsigned int retries;
>  	unsigned int status;
>  	struct edid *edid;
>  	int num = 0;
> @@ -159,7 +161,7 @@ static int sii902x_get_modes(struct drm_connector *connector)
>  		 time_before(jiffies, timeout));
>  
>  	if (!(status & SII902X_SYS_CTRL_DDC_BUS_GRTD)) {
> -		dev_err(&sii902x->i2c->dev, "failed to acquire the i2c bus\n");
> +		dev_err(dev, "failed to acquire the i2c bus\n");
>  		return -ETIMEDOUT;
>  	}
>  
> @@ -179,9 +181,19 @@ static int sii902x_get_modes(struct drm_connector *connector)
>  	if (ret)
>  		return ret;
>  
> -	ret = regmap_read(regmap, SII902X_SYS_CTRL_DATA, &status);
> +	/*
> +	 * Sometimes the I2C bus can stall after failure to use the
> +	 * EDID channel. Retry a few times to see if things clear
> +	 * up, else continue anyway.
> +	 */
> +	retries = 5;
> +	do {
> +		ret = regmap_read(regmap, SII902X_SYS_CTRL_DATA,
> +				  &status);
> +		retries--;
> +	} while (ret && retries);
>  	if (ret)
> -		return ret;
> +		dev_err(dev, "failed to read status (%d)\n", ret);
>  
>  	ret = regmap_update_bits(regmap, SII902X_SYS_CTRL_DATA,
>  				 SII902X_SYS_CTRL_DDC_BUS_REQ |
> @@ -201,7 +213,7 @@ static int sii902x_get_modes(struct drm_connector *connector)
>  
>  	if (status & (SII902X_SYS_CTRL_DDC_BUS_REQ |
>  		      SII902X_SYS_CTRL_DDC_BUS_GRTD)) {
> -		dev_err(&sii902x->i2c->dev, "failed to release the i2c bus\n");
> +		dev_err(dev, "failed to release the i2c bus\n");
>  		return -ETIMEDOUT;
>  	}
>  
> -- 
> 2.14.3
> 

-- 
====================
| I would like to |
| fix the world,  |
| but they're not |
| giving me the   |
 \ source code!  /
  ---------------
    ?\_(?)_/?

[PATCH] drm/bridge: sii902x: Retry status read after DDI I2C

[Linus Walleij]

On Mon, Mar 5, 2018 at 5:05 PM, Liviu Dudau <Liviu.Dudau@arm.com> wrote:

>> Cc: Ville Syrj?l? <ville.syrjala@linux.intel.com>
>> Cc: Liviu Dudau <Liviu.Dudau@arm.com>
>
> I don't have a suitable configuration to test this, but looks goot to me.
>
> Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>

Thanks!

> BTW, Linus, could it be that your DVI-to-VGA connector doesn't wire
> correctly the EDID pin?

Very possible. I also suspect signal levels or something like
that, possibly no proper pull-up resistor on the line. Or
anything similar... it now falls back nicely to default EDID
modes though.

Yours,
Linus Walleij