[Intel-gfx] [PATCH] drm/i915: Shift driver's HWSP usage out of reserved range

[Daniel, Thomas]

> -----Original Message-----
> From: Daniel Vetter [mailto:daniel.vetter at ffwll.ch] On Behalf Of Daniel Vetter
> Sent: Monday, February 23, 2015 11:28 PM
> To: Gordon, David S
> Cc: Daniel, Thomas; intel-gfx at lists.freedesktop.org
> Subject: Re: [Intel-gfx] [PATCH] drm/i915: Shift driver's HWSP usage out of
> reserved range
> 
> On Thu, Feb 19, 2015 at 02:58:48PM +0000, Dave Gordon wrote:
> > On 18/02/15 11:48, Thomas Daniel wrote:
> > > As of Gen6, the general purpose area of the hardware status page has shrunk
> and
> > > now begins at dword 0x30.  i915 driver uses dword 0x20 to store the seqno
> which
> > > is now reserved.  So shift our HWSP dwords up into the general purpose
> range
> > > before this bites us.
> 
> It would be really interesting to know what exactly the hw does with
> offsets below 0x30 ... it might explain some of the bugs we've seen. Can
> you please digg that out so that I can amend the commit message?

All documentation I've seen just says "Reserved" for current hardware including SKL so we can't rely on any particular usage.  That's why I just put "Reserved" for these dwords in the comment.

Thomas.