[Intel-gfx] [PATCH 4/9] drm/i915: add comment about pch pll enabling rules

[Paulo Zanoni]

Hi

2012/10/26 Daniel Vetter <daniel.vetter at ffwll.ch>:
> Atm we have a few funny issues where we enable/disable shared
> pll clocks. To make it clear that we are not required to enable/
> disable the pch plls together with the other pch resources (and
> so should keep it running when it's used by another pipe in
> a shared pll configuration) add a comment.
>
> This note is lifted from "Graphics BSpec: vol4g North Display Engine
> Registers [IVB], Display Mode Set Sequence", step 9.d. of the enable
> sequence:
>
> "Configure and enable PCH DPLL, wait for PCH DPLL warmup (Can be
> done anytime before enabling PCH transcoder)."
>
> Since fixing the pll sharing code to no longer disable shared plls
> if they're still in use is more involved, let's just stick with the
> comment for now.

I'm not sure what's the problem with the current code. Could you
please explain a little bit more? After a brief look at
intel_enable_pch_pll and intel_disable_pch_pll it seems our code does
try to check the pll refcount and behave correctly. I'm not an expert
of the ILK PCH pll sharing code, so I may be missing something.

>
> Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index b19e3bb..aa80ecb 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -3007,6 +3007,9 @@ static void ironlake_pch_enable(struct drm_crtc *crtc)
>         /* For PCH output, training FDI link */
>         dev_priv->display.fdi_link_train(crtc);
>
> +       /* XXX: pch pll's can be enabled any time before we enable the PCH
> +        * transcoder, and we actually should do this to not upset any PCH
> +        * transcoder that already use the clock when we share it. */
>         intel_enable_pch_pll(intel_crtc);
>
>         if (HAS_PCH_LPT(dev)) {
> --
> 1.7.11.4
>
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-- 
Paulo Zanoni