[Intel-gfx] [PATCH v9 1/2] drm/i915: Implement WaProgramMgsrForCorrectSliceSpecificMmioReads

[Chris Wilson]

Quoting Oscar Mateo (2018-04-18 17:30:41)
> 
> 
> On 4/17/2018 3:58 PM, Yunwei Zhang wrote:
> > +     /*
> > +      * HW expects MCR to be programed to a enabled slice/subslice pair
> > +      * before any MMIO read into slice/subslice register
> > +      */
> 
> The comment above makes more sense in sanitize_mcr, together with the WA 
> label. You can make it a bit more verbose with the info in the commit 
> message. Something like this:
> 
> /*
>   * WaProgramMgsrForCorrectSliceSpecificMmioReads:cnl,icl
>   * Before any MMIO read into slice/subslice specific registers, MCR
>   * packet control register needs to be programmed to point to any
>   * enabled s/ss pair. Otherwise, incorrect values will be returned.
>   * This means each subsequent MMIO read will be forwarded to an
>   * specific s/ss combination, but this is OK since these registers
>   * are consistent across s/ss in almost all cases. In the rare
>   * occasions, such as INSTDONE, where this value is dependent
>   * on s/ss combo, the read shoud be done with read_subslice_reg.
>   */
> 
> I don't think any other comment is required here.

Apart from the answer to the earlier question, what mmio read after this
point? If all slice/subslice register access is through this function,
what are you trying to protect? Very curious.
-Chris