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

[Daniel Vetter <daniel@ffwll.ch>]

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