Hi Chris:
There is mapping between i915 cache level -> PPAT index. Currently it's:
static gen8_pte_t gen8_pte_encode(dma_addr_t addr,
enum i915_cache_level level)
{
...
switch (level) {
case I915_CACHE_NONE:
pte |= PPAT_UNCACHED_INDEX;
break;
case I915_CACHE_WT:
pte |= PPAT_DISPLAY_ELLC_INDEX;
break;
default:
pte |= PPAT_CACHED_INDEX;
break;
}
...
According to bspec, the PPAT index filled in the page table is calculated as:
PPAT index = 4 * PAT + 2 * PCD + PWT
In the i915_gem_gtt.c
#define PPAT_UNCACHED_INDEX (_PAGE_PWT | _PAGE_PCD) // PPAT INDEX = 1 + 2 * 1 = 3
#define PPAT_CACHED_PDE_INDEX 0 /* WB LLC */ // PPAT INDEX = 0
#define PPAT_CACHED_INDEX _PAGE_PAT /* WB LLCeLLC */ // PPAT INDEX = 4 * 1 = 4
#define PPAT_DISPLAY_ELLC_INDEX _PAGE_PCD /* WT eLLC */ // PPAT INDEX = 2 * 1 = 2
Actually the PPAT index used by i915 are: 0 2 3 4, which has already been reserved in the RFC patches.
The reason I want to reserve that PPAT entries for host is to keep the mapping between I915_CACHE_* and PPAT_*_INDEX unchanged.
Thanks,
Zhi.
-----Original Message-----
From: Chris Wilson [mailto:chris@xxxxxxxxxxxxxxxxxx]
Sent: Tuesday, August 29, 2017 1:40 PM
To: Wang, Zhi A <zhi.a.wang@xxxxxxxxx>; intel-gfx@xxxxxxxxxxxxxxxxxxxxx; intel-gvt-dev@xxxxxxxxxxxxxxxxxxxxx
Cc: joonas.lahtinen@xxxxxxxxxxxxxxx; zhenyuw@xxxxxxxxxxxxxxx; Wang, Zhi A <zhi.a.wang@xxxxxxxxx>; Widawsky, Benjamin <benjamin.widawsky@xxxxxxxxx>; Vivi, Rodrigo <rodrigo.vivi@xxxxxxxxx>
Subject: Re: [RFCv5 2/2] drm/i915: Introduce private PAT management
Quoting Chris Wilson (2017-08-29 11:05:21)
> Quoting Zhi Wang (2017-08-29 09:00:51)
> > +static void cnl_setup_private_ppat(struct intel_ppat *ppat) {
> > + ppat->max_entries = 8;
> > + ppat->update = cnl_private_pat_update;
> > + ppat->match = bdw_private_pat_match;
> > + ppat->dummy_value = GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(3);
> > +
> > /* XXX: spec is unclear if this is still needed for CNL+ */
> > - if (!USES_PPGTT(dev_priv)) {
> > - I915_WRITE(GEN10_PAT_INDEX(0), GEN8_PPAT_UC);
> > + if (!USES_PPGTT(ppat->i915)) {
> > + alloc_ppat_entry(ppat, 0, GEN8_PPAT_UC);
> > return;
> > }
> >
> > - I915_WRITE(GEN10_PAT_INDEX(0), GEN8_PPAT_WB | GEN8_PPAT_LLC);
> > - I915_WRITE(GEN10_PAT_INDEX(1), GEN8_PPAT_WC | GEN8_PPAT_LLCELLC);
> > - I915_WRITE(GEN10_PAT_INDEX(2), GEN8_PPAT_WT | GEN8_PPAT_LLCELLC);
> > - I915_WRITE(GEN10_PAT_INDEX(3), GEN8_PPAT_UC);
> > - I915_WRITE(GEN10_PAT_INDEX(4), GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(0));
> > - I915_WRITE(GEN10_PAT_INDEX(5), GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(1));
> > - I915_WRITE(GEN10_PAT_INDEX(6), GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(2));
> > - I915_WRITE(GEN10_PAT_INDEX(7), GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(3));
> > + alloc_ppat_entry(ppat, 0, GEN8_PPAT_WB | GEN8_PPAT_LLC);
> > + alloc_ppat_entry(ppat, 2, GEN8_PPAT_WT | GEN8_PPAT_LLCELLC);
> > + alloc_ppat_entry(ppat, 3, GEN8_PPAT_UC);
> > + alloc_ppat_entry(ppat, 4, GEN8_PPAT_LLCELLC |
> > + GEN8_PPAT_AGE(0));
> > }
> >
> > /* The GGTT and PPGTT need a private PPAT setup in order to handle cacheability
> > * bits. When using advanced contexts each context stores its own PAT, but
> > * writing this data shouldn't be harmful even in those cases. */
> > -static void bdw_setup_private_ppat(struct drm_i915_private
> > *dev_priv)
> > +static void bdw_setup_private_ppat(struct intel_ppat *ppat)
> > {
> > - u64 pat;
> > -
> > - pat = GEN8_PPAT(0, GEN8_PPAT_WB | GEN8_PPAT_LLC) | /* for normal objects, no eLLC */
> > - GEN8_PPAT(1, GEN8_PPAT_WC | GEN8_PPAT_LLCELLC) | /* for something pointing to ptes? */
> > - GEN8_PPAT(2, GEN8_PPAT_WT | GEN8_PPAT_LLCELLC) | /* for scanout with eLLC */
> > - GEN8_PPAT(3, GEN8_PPAT_UC) | /* Uncached objects, mostly for scanout */
> > - GEN8_PPAT(4, GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(0)) |
> > - GEN8_PPAT(5, GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(1)) |
> > - GEN8_PPAT(6, GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(2)) |
> > - GEN8_PPAT(7, GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(3));
> > + ppat->max_entries = 8;
> > + ppat->update = bdw_private_pat_update;
> > + ppat->match = bdw_private_pat_match;
> > + ppat->dummy_value = GEN8_PPAT_WB | GEN8_PPAT_LLCELLC |
> > + GEN8_PPAT_AGE(3);
> >
> > - if (!USES_PPGTT(dev_priv))
> > + if (!USES_PPGTT(dev_priv)) {
> > /* Spec: "For GGTT, there is NO pat_sel[2:0] from the entry,
> > * so RTL will always use the value corresponding to
> > * pat_sel = 000".
> > @@ -2864,17 +3038,22 @@ static void bdw_setup_private_ppat(struct drm_i915_private *dev_priv)
> > * So we can still hold onto all our assumptions wrt cpu
> > * clflushing on LLC machines.
> > */
> > - pat = GEN8_PPAT(0, GEN8_PPAT_UC);
> > + alloc_ppat_entry(ppat, 0, GEN8_PPAT_UC);
> > + return;
> > + }
> >
> > - /* XXX: spec defines this as 2 distinct registers. It's unclear if a 64b
> > - * write would work. */
> > - I915_WRITE(GEN8_PRIVATE_PAT_LO, pat);
> > - I915_WRITE(GEN8_PRIVATE_PAT_HI, pat >> 32);
> > + alloc_ppat_entry(ppat, 0, GEN8_PPAT_WB | GEN8_PPAT_LLC); /* for normal objects, no eLLC */
> > + alloc_ppat_entry(ppat, 2, GEN8_PPAT_WT | GEN8_PPAT_LLCELLC); /* for scanout with eLLC */
> > + alloc_ppat_entry(ppat, 3, GEN8_PPAT_UC); /* Uncached objects, mostly for scanout */
> > + alloc_ppat_entry(ppat, 4, GEN8_PPAT_WB | GEN8_PPAT_LLCELLC |
> > + GEN8_PPAT_AGE(0));
> > }
> >
> > -static void chv_setup_private_ppat(struct drm_i915_private
> > *dev_priv)
> > +static void chv_setup_private_ppat(struct intel_ppat *ppat)
> > {
> > - u64 pat;
> > + ppat->max_entries = 8;
> > + ppat->update = bdw_private_pat_update;
> > + ppat->match = chv_private_pat_match;
> > + ppat->dummy_value = CHV_PPAT_SNOOP;
> >
> > /*
> > * Map WB on BDW to snooped on CHV.
> > @@ -2894,17 +3073,11 @@ static void chv_setup_private_ppat(struct drm_i915_private *dev_priv)
> > * Which means we must set the snoop bit in PAT entry 0
> > * in order to keep the global status page working.
> > */
> > - pat = GEN8_PPAT(0, CHV_PPAT_SNOOP) |
> > - GEN8_PPAT(1, 0) |
> > - GEN8_PPAT(2, 0) |
> > - GEN8_PPAT(3, 0) |
> > - GEN8_PPAT(4, CHV_PPAT_SNOOP) |
> > - GEN8_PPAT(5, CHV_PPAT_SNOOP) |
> > - GEN8_PPAT(6, CHV_PPAT_SNOOP) |
> > - GEN8_PPAT(7, CHV_PPAT_SNOOP);
> >
> > - I915_WRITE(GEN8_PRIVATE_PAT_LO, pat);
> > - I915_WRITE(GEN8_PRIVATE_PAT_HI, pat >> 32);
> > + alloc_ppat_entry(ppat, 0, CHV_PPAT_SNOOP);
> > + alloc_ppat_entry(ppat, 2, 0);
> > + alloc_ppat_entry(ppat, 3, 0);
> > + alloc_ppat_entry(ppat, 4, CHV_PPAT_SNOOP);
> > }
>
> 1 is dropped in all cases?
>
> The current ABI is that we reserve (0, 1, 2) for userspace. 1 means
> follow-PTE and is especially important.
Ignore the ABI concern, getting my tables confused. But the question still remains why do we need to reserve these in particular?
-Chris
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