[PATCH] drm/i915: apply WaEnableVGAAccessThroughIOPort as needed

[Ville Syrjälä]

On Fri, Jun 04, 2021 at 04:49:05PM +0100, Emil Velikov wrote:
> From: Emil Velikov <emil.velikov at collabora.com>
> 
> Currently as the workaround is applied the screen flickers. As a result
> we do not achieve seamless boot experience.
> 
> Avoiding the issue in the common use-case might be hard, although we can
> resolve it for dual GPU setups - when the "other" GPU is primary and/or
> outputs are connected to it.
> 
> With this I was able to get seamless experience on my Intel/Nvidia box,
> running systemd-boot and sddm/Xorg. Note that the i915 driver is within
> initrd while the Nvidia one is not.
> 
> Without this patch, the splash presented by systemd-boot (UEFI BGRT) is
> torn down as the code-path kicks in, leaving the monitor blank until the
> login manager starts.
> 
> Same issue were reported with plymouth/grub, although personally I
> wasn't able to get them to behave on my setup.
> 
> Suggested-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Signed-off-by: Emil Velikov <emil.velikov at collabora.com>
> ---

Pushed to drm-intel-next. Thanks.

> 
> Supersedes
> https://lore.kernel.org/dri-devel/20210516171432.1734268-1-emil.l.velikov@gmail.com/
> 
> Ville, others,
> 
> Patch is based against drm-intel/drm-intel-next and will apply cleanly
> against drm-intel/drm-intel-fixes.
> 
> If possible, can one of the i915 maintainers apply it to the latter?
> 
> Thanks
> Emil
> ---
>  drivers/gpu/drm/i915/display/intel_vga.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_vga.c b/drivers/gpu/drm/i915/display/intel_vga.c
> index be333699c515..7beef1206097 100644
> --- a/drivers/gpu/drm/i915/display/intel_vga.c
> +++ b/drivers/gpu/drm/i915/display/intel_vga.c
> @@ -29,6 +29,9 @@ void intel_vga_disable(struct drm_i915_private *dev_priv)
>  	i915_reg_t vga_reg = intel_vga_cntrl_reg(dev_priv);
>  	u8 sr1;
>  
> +	if (intel_de_read(dev_priv, vga_reg) & VGA_DISP_DISABLE)
> +		return;
> +
>  	/* WaEnableVGAAccessThroughIOPort:ctg,elk,ilk,snb,ivb,vlv,hsw */
>  	vga_get_uninterruptible(pdev, VGA_RSRC_LEGACY_IO);
>  	outb(SR01, VGA_SR_INDEX);
> -- 
> 2.31.1

-- 
Ville Syrjälä
Intel