Re: [PATCH 3/3] drm/i915: Make sure vsyncshift is positive

[Jesse Barnes <jbarnes@virtuousgeek.org>]

On Fri, 28 Mar 2014 23:29:32 +0200
ville.syrjala@linux.intel.com wrote:

> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> If vsyncshift comes out as negative, add one htotal to it to get the
> corresponding positive value.
> 
> This is rather theoretical as it would require a mode where the
> hsync+back porch is very long and the active+front porch very short.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 3ab40e3..7d3b18b 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -5377,7 +5377,8 @@ static void intel_set_pipe_timings(struct intel_crtc *intel_crtc)
>  	enum transcoder cpu_transcoder = intel_crtc->config.cpu_transcoder;
>  	struct drm_display_mode *adjusted_mode =
>  		&intel_crtc->config.adjusted_mode;
> -	uint32_t vsyncshift = 0, crtc_vtotal, crtc_vblank_end;
> +	uint32_t crtc_vtotal, crtc_vblank_end;
> +	int vsyncshift = 0;
>  
>  	/* We need to be careful not to changed the adjusted mode, for otherwise
>  	 * the hw state checker will get angry at the mismatch. */
> @@ -5394,6 +5395,8 @@ static void intel_set_pipe_timings(struct intel_crtc *intel_crtc)
>  		else
>  			vsyncshift = adjusted_mode->crtc_hsync_start -
>  				adjusted_mode->crtc_htotal / 2;
> +		if (vsyncshift < 0)
> +			vsyncshift += adjusted_mode->crtc_htotal;
>  	}
>  
>  	if (INTEL_INFO(dev)->gen > 3)


Funky indeed.  I wonder if we should congratulate the user if we detect
this configuration.  "Achievement unlocked: funky mode timings!".

Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>

-- 
Jesse Barnes, Intel Open Source Technology Center
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