Re: [PATCH v2 2/2] drm/i915: resize the GuC WOPCM for rc6

From: Dave Gordon <david.s.gordon@intel.com>
To: Peter Antoine <peter.antoine@intel.com>,
	Jeff McGee <jeff.mcgee@intel.com>
Cc: intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH v2 2/2] drm/i915: resize the GuC WOPCM for rc6
Date: Wed, 3 Feb 2016 15:39:47 +0000	[thread overview]
Message-ID: <56B21F43.9080206@intel.com> (raw)
In-Reply-To: <20160121214140.GB30883@jeffdesk>

On 21/01/16 21:41, Jeff McGee wrote:
> On Thu, Jan 21, 2016 at 06:11:01PM +0000, Peter Antoine wrote:
>> This patch resizes the GuC WOPCM to so that the GuC and the RC6 memory
>> spaces do not overlap.
>>
>> Issue: https://jira01.devtools.intel.com/browse/VIZ-6638
>> Signed-off-by: Peter Antoine <peter.antoine@intel.com>
>> ---
>>   drivers/gpu/drm/i915/i915_guc_reg.h     | 3 ++-
>>   drivers/gpu/drm/i915/intel_guc_loader.c | 6 +++++-
>>   2 files changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_guc_reg.h b/drivers/gpu/drm/i915/i915_guc_reg.h
>> index 685c799..cb938b0 100644
>> --- a/drivers/gpu/drm/i915/i915_guc_reg.h
>> +++ b/drivers/gpu/drm/i915/i915_guc_reg.h
>> @@ -58,7 +58,8 @@
>>   #define GUC_MAX_IDLE_COUNT		_MMIO(0xC3E4)
>>
>>   #define GUC_WOPCM_SIZE			_MMIO(0xc050)
>> -#define   GUC_WOPCM_SIZE_VALUE  	  (0x80 << 12)	/* 512KB */
>> +#define   GUC_WOPCM_SIZE_VALUE		(0x80 << 12)	/* 512KB */
>> +#define   BXT_GUC_WOPCM_SIZE_VALUE	(0x70 << 12)	/* 448KB */
>>
>>   /* GuC addresses below GUC_WOPCM_TOP don't map through the GTT */
>>   #define	GUC_WOPCM_TOP			(GUC_WOPCM_SIZE_VALUE)
> Should GUC_WOPCM_TOP be dynamically assigned the proper value, or is it
> sufficient to leave at the max possible WOPCM size? If the later, might be
> worth a comment.
> -Jeff

This isn't the right interpretation of these values.

GUC_WOPCM_TOP is the value defining the top of the GTT address range NOT 
available to the GuC and hence where GuC-accessible objects must NOT be 
placed.

GUC_WOPCM_SIZE_VALUE is the value written to the GUC_WOPCM_SIZE 
register, defining how much WOPCM space CAN be used.

The former is an architectural constant (512K); the latter is a 
software-defined boundary between areas of memory within that range that 
are used for different purposes.

Therefore, GUC_WOPCM_TOP must NOT be defined in terms of 
GUC_WOPCM_SIZE_VALUE, but GUC_WOPCM_SIZE_VALUE could be defined in terms 
of GUC_WOPCM_TOP, in particular as (GUC_WOPCM_TOP-reserved).

.Dave.
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