[Intel-gfx] [PATCH 1/2] drm/i915: check for power well in redisable VGA with generic fn

[Paulo Zanoni]

2013/10/11 Jesse Barnes <jbarnes at virtuousgeek.org>:
> Rather than using a HSW specific check.
>
> Signed-off-by: Jesse Barnes <jbarnes at virtuousgeek.org>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 53c4ea8..5452b34 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -10667,8 +10667,7 @@ void i915_redisable_vga(struct drm_device *dev)
>          * level, just check if the power well is enabled instead of trying to
>          * follow the "don't touch the power well if we don't need it" policy
>          * the rest of the driver uses. */
> -       if (HAS_POWER_WELL(dev) &&
> -           (I915_READ(HSW_PWR_WELL_DRIVER) & HSW_PWR_WELL_STATE_ENABLED) == 0)
> +       if (!intel_display_power_enabled(dev, POWER_DOMAIN_VGA))

See the big comment. With your patch we're not only going to return in
case the power well is disabled, we're going to return in case it's
disabled _or_ we promised to not touch it (even if it's enabled). I
originally made the same mistake, then Ville spotted it on the code
review. This function should assume the BIOS is being an idiot and is
trying to mess with us.

I admit I don't like it, suggestions to further improve this code are
welcome. But it seems no one really knows what's the best and safest
thing to do here :(

>                 return;
>
>         if (I915_READ(vga_reg) != VGA_DISP_DISABLE) {
> --
> 1.8.3.1
>
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-- 
Paulo Zanoni