[Intel-gfx] [PATCH 2/2] drm/i915: Fail addfb ioctl if color and CCS buffers overlap

[Gabriel Krisman Bertazi]

Ville Syrjälä <ville.syrjala at linux.intel.com> writes:

> On Tue, Sep 05, 2017 at 08:36:54AM +0100, Daniel Stone wrote:
>> Hi Ville,
>> 
>> On 4 September 2017 at 17:37, Ville Syrjälä
>> <ville.syrjala at linux.intel.com> wrote:
>> > On Thu, Aug 31, 2017 at 04:52:15PM -0300, Gabriel Krisman Bertazi wrote:
>> >> With this patch the new testcase igt at kms_ccs@pipe-X-invalid-ccs-offset
>> >> succeeds.
>> >
>> > I don't think we actually want to reject overlap. I had a patch for that
>> > years ago, but I decided to drop it because people might want to
>> > interleave the planes in some interesting ways. Making the overlap
>> > check accurate enough to allow that would be to total overkill. So IMO
>> > it's perfectly fine to let the user shoot himself in the foot if they
>> > mess up the offsets.
>> 
>> Is that actually supported by any hardware renderer? If not, maybe the
>> check should only be enabled for generations who support it.
>
> Not sure I understand the question. You can program your offsets/strides
> any which way you want,

Hi Ville,

Sorry for the delay.  Reviewing documentation at [1] I see the
following, in page 177, regarding CCS structure:
"The CCS is always placed after the main surface and is 4K page
aligned".  Sorry if I am missing something, but I believe this indicates
we can reject any overlapping between the main buffer and CCS. Can you
explain why not?

[1] https://01.org/sites/default/files/documentation/intel-gfx-prm-osrc-kbl-vol12-display.pdf

-- 
Gabriel Krisman Bertazi