Re: [PATCH v3 07/15] drm/i915: Add functions to allocate / release gem obj for GuC

Yu Dai
2015-04-20T16:03:31Z

On 04/18/2015 06:47 AM, Chris Wilson wrote:
> On Fri, Apr 17, 2015 at 02:21:12PM -0700, yu.dai@intel.com wrote:
> > From: Alex Dai <yu.dai@intel.com>
> >
> > All gem objects used by GuC are pinned to ggtt space out of range
> > [0, WOPCM size]. In GuC address space mapping, [0, WPOCM size] is
> > used internally for its Boot ROM, SRAM etc. Currently this WPOCM
> > size is 512K. This is done by using of PIN_OFFSET_BIAS.
>
> If the region is reserved, remove that region from the GGTT drm_mm range
> manager. Then the restriction is applied to all objects and not in a
> hodge-podge fashion like this.
>
I don't think I have clearly explained this. GTT range [0, WPOCM size]
can't be used by GuC firmware, but still others can use it without any
issue. PIN_OFFSET_BIAS is great for such use case.