[DVO][PATCH] drm/i915: Fall back to bit banging mode for DVO transmitter detection

[DVO][PATCH] drm/i915: Fall back to bit banging mode for DVO transmitter detection

["David Müller (ELSOFT AG)"]

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Hello

As discussed in this thread
http://lists.freedesktop.org/archives/dri-devel/2013-April/037411.html
GMBUS based DVO transmitter detection seems to be unreliable which could
result in an unusable DVO port.

The attached patch fixes this by falling back to bit banging mode for
the time DVO transmitter detection is in progress.


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Signed-off-by: David Müller <d.mueller@elsoft.ch>
Tested-by: David Müller <d.mueller@elsoft.ch>

---
diff -dpurN a/drivers/gpu/drm/i915/intel_dvo.c b/drivers/gpu/drm/i915/intel_dvo.c
--- a/drivers/gpu/drm/i915/intel_dvo.c	2012-12-11 10:09:35.113446850 +0100
+++ b/drivers/gpu/drm/i915/intel_dvo.c	2013-04-19 07:21:54.054546365 +0200
@@ -449,6 +449,7 @@ void intel_dvo_init(struct drm_device *d
 		const struct intel_dvo_device *dvo = &intel_dvo_devices[i];
 		struct i2c_adapter *i2c;
 		int gpio;
+		bool dvoinit;
 
 		/* Allow the I2C driver info to specify the GPIO to be used in
 		 * special cases, but otherwise default to what's defined
@@ -468,7 +469,17 @@ void intel_dvo_init(struct drm_device *d
 		i2c = intel_gmbus_get_adapter(dev_priv, gpio);
 
 		intel_dvo->dev = *dvo;
-		if (!dvo->dev_ops->init(&intel_dvo->dev, i2c))
+
+		/* GMBUS NAK handling seems to be unstable, hence let the
+		 * transmitter detection run in bit banging mode for now.
+		 */
+		intel_gmbus_force_bit(i2c, true);
+
+		dvoinit = dvo->dev_ops->init(&intel_dvo->dev, i2c);
+
+		intel_gmbus_force_bit(i2c, false);
+
+		if (!dvoinit)
 			continue;
 
 		intel_encoder->type = INTEL_OUTPUT_DVO;

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Re: [DVO][PATCH] drm/i915: Fall back to bit banging mode for DVO transmitter detection

[Daniel Vetter]

On Fri, Apr 19, 2013 at 10:41:50AM +0200, "David Müller (ELSOFT AG)" wrote:
> Hello
> 
> As discussed in this thread
> http://lists.freedesktop.org/archives/dri-devel/2013-April/037411.html
> GMBUS based DVO transmitter detection seems to be unreliable which could
> result in an unusable DVO port.
> 
> The attached patch fixes this by falling back to bit banging mode for
> the time DVO transmitter detection is in progress.
> 

> Signed-off-by: David Müller <d.mueller@elsoft.ch>
> Tested-by: David Müller <d.mueller@elsoft.ch>
> 
> ---
> diff -dpurN a/drivers/gpu/drm/i915/intel_dvo.c b/drivers/gpu/drm/i915/intel_dvo.c
> --- a/drivers/gpu/drm/i915/intel_dvo.c	2012-12-11 10:09:35.113446850 +0100
> +++ b/drivers/gpu/drm/i915/intel_dvo.c	2013-04-19 07:21:54.054546365 +0200
> @@ -449,6 +449,7 @@ void intel_dvo_init(struct drm_device *d
>  		const struct intel_dvo_device *dvo = &intel_dvo_devices[i];
>  		struct i2c_adapter *i2c;
>  		int gpio;
> +		bool dvoinit;
>  
>  		/* Allow the I2C driver info to specify the GPIO to be used in
>  		 * special cases, but otherwise default to what's defined
> @@ -468,7 +469,17 @@ void intel_dvo_init(struct drm_device *d
>  		i2c = intel_gmbus_get_adapter(dev_priv, gpio);
>  
>  		intel_dvo->dev = *dvo;
> -		if (!dvo->dev_ops->init(&intel_dvo->dev, i2c))
> +
> +		/* GMBUS NAK handling seems to be unstable, hence let the
> +		 * transmitter detection run in bit banging mode for now.
> +		 */
> +		intel_gmbus_force_bit(i2c, true);
> +
> +		dvoinit = dvo->dev_ops->init(&intel_dvo->dev, i2c);
> +
> +		intel_gmbus_force_bit(i2c, false);

Shouldn't we keep the dvo i2c line in bit-banging mode always, i.e.
restore gmbus mode only when dvo init failed?

I suspect that for fickle hw not just init will fail ...
-Daniel

> +
> +		if (!dvoinit)
>  			continue;
>  
>  		intel_encoder->type = INTEL_OUTPUT_DVO;


-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch

Re: [DVO][PATCH] drm/i915: Fall back to bit banging mode for DVO transmitter detection

["David Müller (ELSOFT AG)"]

Daniel Vetter wrote:
> On Fri, Apr 19, 2013 at 10:41:50AM +0200, "David Müller (ELSOFT AG)" wrote:
>> +		/* GMBUS NAK handling seems to be unstable, hence let the
>> +		 * transmitter detection run in bit banging mode for now.
>> +		 */
>> +		intel_gmbus_force_bit(i2c, true);
>> +
>> +		dvoinit = dvo->dev_ops->init(&intel_dvo->dev, i2c);
>> +
>> +		intel_gmbus_force_bit(i2c, false);
> 
> Shouldn't we keep the dvo i2c line in bit-banging mode always, i.e.
> restore gmbus mode only when dvo init failed?
> 
> I suspect that for fickle hw not just init will fail ...

As far as i can tell, the critical part is the NAK handling.

Dave

Re: [DVO][PATCH] drm/i915: Fall back to bit banging mode for DVO transmitter detection

[Daniel Vetter]

On Fri, Apr 19, 2013 at 12:54:00PM +0200, "David Müller (ELSOFT AG)" wrote:
> Daniel Vetter wrote:
> > On Fri, Apr 19, 2013 at 10:41:50AM +0200, "David Müller (ELSOFT AG)" wrote:
> >> +		/* GMBUS NAK handling seems to be unstable, hence let the
> >> +		 * transmitter detection run in bit banging mode for now.
> >> +		 */
> >> +		intel_gmbus_force_bit(i2c, true);
> >> +
> >> +		dvoinit = dvo->dev_ops->init(&intel_dvo->dev, i2c);
> >> +
> >> +		intel_gmbus_force_bit(i2c, false);
> > 
> > Shouldn't we keep the dvo i2c line in bit-banging mode always, i.e.
> > restore gmbus mode only when dvo init failed?
> > 
> > I suspect that for fickle hw not just init will fail ...
> 
> As far as i can tell, the critical part is the NAK handling.

Ok, I've merged the patch for 3.10 with cc: stable.

Thanks, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch