[Intel-gfx] [PATCH v5 1/2] drm/i915/cnl: Implement WaProgramMgsrForCorrectSliceSpecificMmioReads

[Chris Wilson]

Quoting Zhang, Yunwei (2018-03-27 23:49:27)
> 
> 
> On 3/27/2018 3:27 PM, Chris Wilson wrote:
> > Quoting Yunwei Zhang (2018-03-27 23:14:16)
> >> WaProgramMgsrForCorrectSliceSpecificMmioReads dictate that before any MMIO
> >> read into Slice/Subslice specific registers, MCR packet control
> >> register(0xFDC) needs to be programmed to point to any enabled
> >> slice/subslice pair. Otherwise, incorrect value will be returned.
> >>
> >> However, that means each subsequent MMIO read will be forwarded to a
> >> specific slice/subslice combination as read is unicast. This is OK since
> >> slice/subslice specific register values are consistent in almost all cases
> >> across slice/subslice. There are rare occasions such as INSTDONE that this
> >> value will be dependent on slice/subslice combo, in such cases, we need to
> >> program 0xFDC and recover this after. This is already covered by
> >> read_subslice_reg.
> >>
> >> Also, 0xFDC will lose its information after TDR/engine reset/power state
> >> change.
> >>
> >> References: HSD#1405586840, BSID#0575
> >>
> >> v2:
> >>   - use fls() instead of find_last_bit() (Chris)
> >>   - added INTEL_SSEU to extract sseu from device info. (Chris)
> >> v3:
> >>   - rebase on latest tip
> >> v5:
> >>   - Added references (Mika)
> >>   - Change the ordered of passing arguments and etc. (Ursulin)
> >>
> >> Cc: Oscar Mateo <oscar.mateo at intel.com>
> >> Cc: Michel Thierry <michel.thierry at intel.com>
> >> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> >> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> >> Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> >> Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
> >> Signed-off-by: Yunwei Zhang <yunwei.zhang at intel.com>
> >> ---
> >>   drivers/gpu/drm/i915/intel_engine_cs.c | 39 ++++++++++++++++++++++++++++++++--
> >>   1 file changed, 37 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
> >> index de09fa4..4c78d1e 100644
> >> --- a/drivers/gpu/drm/i915/intel_engine_cs.c
> >> +++ b/drivers/gpu/drm/i915/intel_engine_cs.c
> >> @@ -796,6 +796,27 @@ const char *i915_cache_level_str(struct drm_i915_private *i915, int type)
> >>          }
> >>   }
> >>   
> >> +static u32 calculate_mcr(struct drm_i915_private *dev_priv, u32 mcr)
> >> +{
> >> +       const struct sseu_dev_info *sseu = &(INTEL_INFO(dev_priv)->sseu);
> >> +       u32 slice = fls(sseu->slice_mask);
> >> +       u32 subslice = fls(sseu->subslice_mask[slice]);
> >> +
> >> +       mcr &= ~(GEN8_MCR_SLICE_MASK | GEN8_MCR_SUBSLICE_MASK);
> >> +       mcr |= GEN8_MCR_SLICE(slice) | GEN8_MCR_SUBSLICE(subslice);
> >> +
> >> +       return mcr;
> >> +}
> >> +
> >> +static void wa_init_mcr(struct drm_i915_private *dev_priv)
> >> +{
> >> +       u32 mcr;
> >> +
> >> +       mcr = I915_READ(GEN8_MCR_SELECTOR);
> >> +       mcr = calculate_mcr(dev_priv, mcr);
> >> +       I915_WRITE(GEN8_MCR_SELECTOR, mcr);
> >> +}
> >> +
> >>   static inline uint32_t
> >>   read_subslice_reg(struct drm_i915_private *dev_priv, int slice,
> >>                    int subslice, i915_reg_t reg)
> >> @@ -828,18 +849,29 @@ read_subslice_reg(struct drm_i915_private *dev_priv, int slice,
> >>          intel_uncore_forcewake_get__locked(dev_priv, fw_domains);
> >>   
> >>          mcr = I915_READ_FW(GEN8_MCR_SELECTOR);
> >> +
> >>          /*
> >>           * The HW expects the slice and sublice selectors to be reset to 0
> >>           * after reading out the registers.
> >>           */
> >> -       WARN_ON_ONCE(mcr & mcr_slice_subslice_mask);
> >> +       WARN_ON_ONCE(INTEL_GEN(dev_priv) < 10 &&
> >> +                    (mcr & mcr_slice_subslice_mask));
> >>          mcr &= ~mcr_slice_subslice_mask;
> >>          mcr |= mcr_slice_subslice_select;
> >>          I915_WRITE_FW(GEN8_MCR_SELECTOR, mcr);
> >>   
> >>          ret = I915_READ_FW(reg);
> >>   
> >> -       mcr &= ~mcr_slice_subslice_mask;
> >> +       /*
> >> +        * WaProgramMgsrForCorrectSliceSpecificMmioReads:cnl
> >> +        * expects mcr to be programed to a enabled slice/subslice pair
> >> +        * before any MMIO read into slice/subslice register
> >> +        */
> > So the read was above, where we did set the subslice_select
> > appropriately. Here we are resetting back to 0 *after* the read, as the
> > comment before indicates.
> >
> > So what are you trying to accomplish with this patch? Other than leaving
> > the code in conflict with itself.
> > -Chris
> Hi Chris,
> 
> The comment mentioned 0xFDC needs to be reset to 0 was before this WA 
> was introduced, in later HW, this WA requires 0xFDC to be programmed to 
> a enabled slice/subslice.
> 
> What this patch does it to initialize 0xFDC once at the initialization 
> (also it will be called after engine reset/TDR/coming out of c6) and 
> make sure every time it is changed, it will be reprogrammed to a enabled 
> slice/subslice so that a MMIO
> read will get the correct value. read_subslice_reg changes the 0xFDC 
> value and if it is set to 0, it will cause MMIO read to return invalid 
> value for s/ss specific registers.

What mmio read? The only accessor should be this function.

And still the two comments are in direct conflict with each other.
-Chris