[Mesa-dev] [android-x86-devel] Re: gralloc_drm_pipe

[Rob Herring]

On Tue, Mar 29, 2016 at 8:43 AM, Rob Clark <robdclark at gmail.com> wrote:
> On Mon, Mar 28, 2016 at 12:29 PM, Rob Herring <robh at kernel.org> wrote:
>> On Fri, Mar 25, 2016 at 8:38 PM, Stéphane Marchesin <marcheu at google.com> wrote:
>>> On Wed, Mar 23, 2016 at 5:22 PM, Rob Herring <robh at kernel.org> wrote:
>>>> On Fri, Mar 4, 2016 at 12:07 PM, Rob Clark <robdclark at gmail.com> wrote:
>>>>> On Fri, Mar 4, 2016 at 12:59 PM, Rob Clark <robdclark at gmail.com> wrote:
>>>>>> So, I've been advocating that for android, gallium drivers use
>>>>>> gralloc_drm_pipe, since with android it seems like you end up with
>>>>>> both gralloc and libGL in the same process, and having both share the
>>>>>> same pipe_screen avoids lots of headaches with multiple gem handles
>>>>>> pointing to same underlying buffer.
>>>>>>
>>>>>> But the awkward thing is that gralloc_drm_pipe is using gallium APIs
>>>>>> that aren't particularly intended to be used out-of-tree.  Ie. not
>>>>>> really stable APIs.  At the time, the thing that made sense to me was
>>>>>> to pull drm_gralloc into mesa.  But at the time, there were no
>>>>>> non-mesa users of drm_gralloc, which isn't really true anymore.
>>>>>>
>>>>>> Maybe what makes more sense now is to implement a gralloc state
>>>>>> tracker, which exposes a stable API for drm_gralloc?  It would mostly
>>>>>> be a shim to expose gallium import/export/transfer APIs in a stable
>>>>>> way, but would also be where the code that figures out which driver to
>>>>>> use to create/get the pipe_screen.
>>>>>
>>>>> and actually, we might just be able to use XA state tracker for this..
>>>>> I think it exposes all the necessary import/export/etc stuff that
>>>>> gralloc would need..
>>>>
>>>> Rob and I discussed this a bit more F2F recently. An alternative we
>>>> discussed would be using GBM instead. GBM seems more inline with
>>>> gralloc needs. This would also have the advantage of working with
>>>> minigbm as well for non-mesa cases. Any thoughts on GBM vs. XA?
>>>
>>> gbm as it is misses some bits, for example lock/unlock, and more fine
>>> grained usage flags.
>>
>> I think this can be implemented on top within gralloc as it is today
>> with drm_gralloc.
>>
>> However, I found a bigger mismatch is there are no explicit map/unmap
>> calls in GBM. A writeable buffer will be a dumb buffer and is
>> implicitly mapped. Maybe that is enough in reality?
>>
>
> I think originally this was probably just used for uploading mouse
> cursor, or something along those lines, rather than any serious use of
> sw rendering.  But if android needs to mix hw and sw access to the
> buffer, I think we do need something that maps to transfer_map/unmap,
> so gl driver can (if needed) flush pending rendering and sync.
>
> Not sure how others feel, but I wouldn't be opposed to extending gbm..
> anything that can sit on top of transfer_map/unmap should coexist well
> with a gpu driver.

Looks like it was tried already[1]. Interestingly, the gralloc lock
interface already does some of what is discussed being needed
(specifying the region).

Rob

[1] https://lists.freedesktop.org/archives/mesa-dev/2014-April/058484.html