[Intel-gfx] [PATCH 1/5] drm/i915: redisable VGA when we disable the power well

[Ville Syrjälä]

On Thu, Sep 26, 2013 at 08:05:58PM -0300, Paulo Zanoni wrote:
> From: Paulo Zanoni <paulo.r.zanoni at intel.com>
> 
> VGA whack-a-mole!
> 
> We need VGA to be disabled whenever our driver is working. So even
> without reproducible bugs this patch makes sense, but we do have a bug
> solved by this patch.
> 
> If you boot a Haswell machine with eDP+HDMI, then kill your display
> manager and run:
>     echo 0 > /sys/class/vtconsole/vtcon1/bind
> you'll get thousands of "unclaimed register" messages. Notice that
> since we have eDP+HDMI, the power well is *enabled* when we run the
> command, but if you look at dmesg you'll see that at some point during
> the boot we disabled it and then reenabled it. This patch solves this
> problem.
> 
> I didn't do a deep analysis of the problem, but I guess vgacon gets
> seriously confused when it sees that the VGA plane is enabled.
> 
> Besides the command above, this problem can also be reproduced by the
> "module_reload" test from intel-gpu-tools.
> 
> Fixes regression introduced by:
>     commit bf51d5e2cda5d36d98e4b46ac7fca9461e512c41
>     Author: Paulo Zanoni <paulo.r.zanoni at intel.com>
>         drm/i915: switch disable_power_well default value to 1
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=67813
> Signed-off-by: Paulo Zanoni <paulo.r.zanoni at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 2 +-
>  drivers/gpu/drm/i915/intel_drv.h     | 1 +
>  drivers/gpu/drm/i915/intel_pm.c      | 6 ++++++
>  3 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 665fa8f..065ffed 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -10232,7 +10232,7 @@ static void intel_init_quirks(struct drm_device *dev)
>  }
>  
>  /* Disable the VGA plane that we never use */
> -static void i915_disable_vga(struct drm_device *dev)
> +void i915_disable_vga(struct drm_device *dev)
>  {
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  	u8 sr1;
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index a17a86a..e63646a 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -678,6 +678,7 @@ void
>  ironlake_check_encoder_dotclock(const struct intel_crtc_config *pipe_config,
>  				int dotclock);
>  bool intel_crtc_active(struct drm_crtc *crtc);
> +void i915_disable_vga(struct drm_device *dev);
>  void i915_disable_vga_mem(struct drm_device *dev);
>  
>  
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 2ac1c2f..7a8af95 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -5329,6 +5329,12 @@ static void __intel_set_power_well(struct drm_device *dev, bool enable)
>  			if (wait_for((I915_READ(HSW_PWR_WELL_DRIVER) &
>  				      HSW_PWR_WELL_STATE_ENABLED), 20))
>  				DRM_ERROR("Timeout enabling power well\n");
> +
> +			if (I915_READ(i915_vgacntrl_reg(dev)) !=
> +			    VGA_DISP_DISABLE) {
> +				i915_disable_vga(dev);
> +				i915_disable_vga_mem(dev);
> +			}

Hmm. That makes no sense.

So somehow the thrice cursed BIOS re-enabled the VGA plane behind our
back? That really shouldn't cause any problems other than maybe
corrupting the display or something. In any case it has nothing to do
with vga resource decode.

The real problem seems to be that vgacon is poking at vga resources we
apparently decode but can't handle. If your patch really fixes it then
it would seem to BIOS also enabled VGA memory decode. But that still
doesn't explain the unclaimed register errors, as that would require
the power well to be off. But since you say HDMI is enabled, the power
well must be on as well. So all I can say is wtf?

>  		}
>  	} else {
>  		if (enable_requested) {
> -- 
> 1.8.3.1
> 
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-- 
Ville Syrjälä
Intel OTC