Re: [PATCH v2 02/15] drm/i915/dsb: DSB context creation.

From: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
To: Animesh Manna <animesh.manna@intel.com>, intel-gfx@lists.freedesktop.org
Cc: Jani Nikula <jani.nikula@intel.com>
Subject: Re: [PATCH v2 02/15] drm/i915/dsb: DSB context creation.
Date: Thu, 17 Oct 2019 09:35:23 +0100	[thread overview]
Message-ID: <ce725ae5-0414-deee-cf05-dd668ee4dc6e@linux.intel.com> (raw)
In-Reply-To: <156647579816.20466.12274548195324928413@skylake-alporthouse-com>

On 22/08/2019 13:09, Chris Wilson wrote:
> Quoting Animesh Manna (2019-08-22 13:05:06)
>> Hi,
>>
>>
>> On 8/21/2019 11:41 PM, Chris Wilson wrote:
>>> Quoting Animesh Manna (2019-08-21 07:32:22)
>>>> +       vma = i915_gem_object_ggtt_pin(obj, NULL, 0, 0, PIN_MAPPABLE);
>>> Only this (currently) still requires struct_mutex
>>
>> Sure will add.
>>>
>>> Does it have to mappable? Is that the HW constraint?
>>
>> Yes, as per HW design need a cpu mapped buffer to write opcode+data from
>> driver.
> 
> PIN_MAPPABLE refers to the iomem aperture portion of the Global GTT (i.e.
> the low 64-512MiB). You never use a GGTT mmap for your CPU access, so the
> placement should be entirely dictated by the DSB requirements. If you
> don't need to be in the low region, don't force it to be, so we have
> less congestion for the objects that have to be placed in that region.

I was doing a mini audit of what uses the aperture these days and 
noticed this code has been merged in the meantime, but AFAICS this 
question from Chris hasn't been answered? At least not on the mailing 
list. So does it need to be in the aperture region or not?

Regards,

Tvrtko
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