Re: [PATCH v16 1/4] drm/i915: Introduce private PAT management

[Joonas Lahtinen <joonas.lahtinen@linux.intel.com>]

On Wed, 2017-09-13 at 16:44 +0800, Zhi Wang wrote:
> The private PAT management is to support PPAT entry manipulation. Two
> APIs are introduced for dynamically managing PPAT entries: intel_ppat_get
> and intel_ppat_put.
> 
> intel_ppat_get will search for an existing PPAT entry which perfectly
> matches the required PPAT value. If not, it will try to allocate a new
> entry if there is any available PPAT indexs, or return a partially
> matched PPAT entry if there is no available PPAT indexes.
> 
> intel_ppat_put will put back the PPAT entry which comes from
> intel_ppat_get. If it's dynamically allocated, the reference count will
> be decreased. If the reference count turns into zero, the PPAT index is
> freed again.
> 
> Besides, another two callbacks are introduced to support the private PAT
> management framework. One is ppat->update_hw(), which writes the PPAT
> configurations in ppat->entries into HW. Another one is ppat->match, which
> will return a score to show how two PPAT values match with each other.
> 
> v16:
> 
> - Fix a bug in PPAT match function of BDW. (Joonas)
> 
> v15:
> 
> - Refine some code flow. (Joonas)
> 
> v12:
> 
> - Fix a problem "not returning the entry of best score". (Zhenyu)
> 
> v7:
> 
> - Keep all the register writes unchanged in this patch. (Joonas)
> 
> v6:
> 
> - Address all comments from Chris:
> http://www.spinics.net/lists/intel-gfx/msg136850.html
> 
> - Address all comments from Joonas:
> http://www.spinics.net/lists/intel-gfx/msg136845.html
> 
> v5:
> 
> - Add check and warnnings for those platforms which don't have PPAT.
> 
> v3:
> 
> - Introduce dirty bitmap for PPAT registers. (Chris)
> - Change the name of the pointer "dev_priv" to "i915". (Chris)
> - intel_ppat_{get, put} returns/takes a const intel_ppat_entry *. (Chris)
> 
> v2:
> 
> - API re-design. (Chris)
> 
> Signed-off-by: Zhi Wang <zhi.a.wang@intel.com>
> Cc: Ben Widawsky <benjamin.widawsky@intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> #v7
> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

<SNIP>

> +static unsigned int bdw_private_pat_match(u8 src, u8 dst)
> +{
> +	unsigned int score = 0;
> +
> +	/* Cache attribute has to be matched. */
> +	if (GEN8_PPAT_GET_CA(src) != GEN8_PPAT_GET_CA(dst))
> +		return 0;
> +
> +	score += 4;
> +
> +	if (GEN8_PPAT_GET_TC(src) == GEN8_PPAT_GET_TC(dst))
> +		score += 2;
> +
> +	if (GEN8_PPAT_GET_AGE(src) == GEN8_PPAT_GET_AGE(dst))
> +		score += 1;
> +
> +	if (score == 3)
> +		return INTEL_PPAT_PERFECT_MATCH;

This still needs to check for 7 to trigger the fast-path. A
future-proof way would be;

	return score >= 7 ? INTEL_PPAT_PERFECT_MATCH :
			    score;

Regards, Joonas
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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