[Intel-gfx] [PATCH] drm/i915/pch: Save/restore PCH_PORT_HOTPLUG across suspend

[Jesse Barnes]

On Tue, 26 Jul 2011 16:53:06 -0400
Adam Jackson <ajax at redhat.com> wrote:

> At least on a Lenovo X220 the HPD bits of this are enabled at boot but
> cleared after resume, which means plug interrupts stop working.
> 
> This also happens to fix DP displays re-lighting on resume.  I'm quite
> certain that's an accident: the first DP link train inevitably fails on
> that machine, and it's only serendipity that we're getting multiple plug
> interrupts and the second train works.  But I shall take my victories
> where I get them.
> 
> Signed-off-by: Adam Jackson <ajax at redhat.com>
> ---
>  drivers/gpu/drm/i915/i915_drv.h     |    1 +
>  drivers/gpu/drm/i915/i915_suspend.c |    2 ++
>  2 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index cf30f99..6b93fa5 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -541,6 +541,7 @@ typedef struct drm_i915_private {
>  	u32 savePIPEB_LINK_M1;
>  	u32 savePIPEB_LINK_N1;
>  	u32 saveMCHBAR_RENDER_STANDBY;
> +	u32 savePCH_PORT_HOTPLUG;
>  
>  	struct {
>  		/** Bridge to intel-gtt-ko */
> diff --git a/drivers/gpu/drm/i915/i915_suspend.c b/drivers/gpu/drm/i915/i915_suspend.c
> index 5257cfc..27693c0 100644
> --- a/drivers/gpu/drm/i915/i915_suspend.c
> +++ b/drivers/gpu/drm/i915/i915_suspend.c
> @@ -814,6 +814,7 @@ int i915_save_state(struct drm_device *dev)
>  		dev_priv->saveFDI_RXB_IMR = I915_READ(_FDI_RXB_IMR);
>  		dev_priv->saveMCHBAR_RENDER_STANDBY =
>  			I915_READ(RSTDBYCTL);
> +		dev_priv->savePCH_PORT_HOTPLUG = I915_READ(PCH_PORT_HOTPLUG);
>  	} else {
>  		dev_priv->saveIER = I915_READ(IER);
>  		dev_priv->saveIMR = I915_READ(IMR);
> @@ -865,6 +866,7 @@ int i915_restore_state(struct drm_device *dev)
>  		I915_WRITE(GTIMR, dev_priv->saveGTIMR);
>  		I915_WRITE(_FDI_RXA_IMR, dev_priv->saveFDI_RXA_IMR);
>  		I915_WRITE(_FDI_RXB_IMR, dev_priv->saveFDI_RXB_IMR);
> +		I915_WRITE(PCH_PORT_HOTPLUG, dev_priv->savePCH_PORT_HOTPLUG);
>  	} else {
>  		I915_WRITE(IER, dev_priv->saveIER);
>  		I915_WRITE(IMR, dev_priv->saveIMR);

We should be writing this reg.  The only question is whether we should
be trusting the BIOS values (which may have custom pulse duration
settings) or just unconditionally enabling hot plug for ports we care
about with the default 2ms pulse width (per the DP spec).

If we assume the BIOS programs this reg to a good value (a very big
assumption) saving and restoring it is safest.  I just wonder if we'll
find machines where it's broken by default leading to weird DP behavior.

-- 
Jesse Barnes, Intel Open Source Technology Center