[Intel-gfx] [PATCH 1/4] drm/i915/display: Handle fused off display correctly

[Ville Syrjälä]

On Thu, Oct 10, 2019 at 12:32:38PM -0700, José Roberto de Souza wrote:
> If all pipes are fused off it means that display is disabled, similar
> like we handle for GEN 7 and 8 right above.
> 
> On GEN 9 the bit 31 is "Internal Graphics Disable" and on newer GENs
> it has another function, probably on GEN 9 when bit 31 is set all
> the 3 pipes disable bit are set, so we can unify the handling.

I'm not sure this is really correct. The description says the pipe will
just output a solid color, so the display hardware may be there to some
degree and if we don't want to waste power we may have to power manage
some of it still.

Not sure how high up we've plugged in the 'pipe_mask==0 -> display not
there' logic. If it's too high up we may leave some power on the floor.

But all that is just speculation on my part. Would probably be good
to get some clarification to the spec about this stuff.

> 
> Cc: Lucas De Marchi <lucas.demarchi at intel.com>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Signed-off-by: José Roberto de Souza <jose.souza at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_device_info.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_device_info.c b/drivers/gpu/drm/i915/intel_device_info.c
> index 85e480bdc673..c01fccfe3cca 100644
> --- a/drivers/gpu/drm/i915/intel_device_info.c
> +++ b/drivers/gpu/drm/i915/intel_device_info.c
> @@ -972,15 +972,14 @@ void intel_device_info_runtime_init(struct drm_i915_private *dev_priv)
>  			enabled_mask &= ~BIT(PIPE_D);
>  
>  		/*
> -		 * At least one pipe should be enabled and if there are
> -		 * disabled pipes, they should be the last ones, with no holes
> -		 * in the mask.
> +		 * If there are disabled pipes, they should be the last ones,
> +		 * with no holes in the mask.
>  		 */
> -		if (enabled_mask == 0 || !is_power_of_2(enabled_mask + 1))
> +		if (enabled_mask && !is_power_of_2(enabled_mask + 1))
>  			DRM_ERROR("invalid pipe fuse configuration: enabled_mask=0x%x\n",
>  				  enabled_mask);
> -		else
> -			info->pipe_mask = enabled_mask;
> +
> +		info->pipe_mask = enabled_mask;
>  	}
>  
>  	/* Initialize slice/subslice/EU info */
> -- 
> 2.23.0

-- 
Ville Syrjälä
Intel