[Mesa-dev] [PATCH v1 0/7] Implement commont gralloc_handle_t in libdrm

[Tomasz Figa]

Hi Rob,

On Fri, Feb 16, 2018 at 11:48 PM, Tomasz Figa <tfiga at chromium.org> wrote:
> On Fri, Feb 16, 2018 at 11:33 PM, Robert Foss <robert.foss at collabora.com> wrote:
>> Hey Tomasz,
>>
>>
>> On 02/16/2018 05:10 AM, Tomasz Figa wrote:
>>>
>>> On Fri, Feb 9, 2018 at 11:06 PM, Rob Herring <robh at kernel.org> wrote:
>>>>
>>>> On Fri, Feb 9, 2018 at 3:58 AM, Tomasz Figa <tfiga at chromium.org> wrote:
>>>>>
>>>>> On Fri, Feb 2, 2018 at 11:51 PM, Tomasz Figa <tfiga at chromium.org> wrote:
>>>>>>
>>>>>> On Fri, Feb 2, 2018 at 11:00 PM, Rob Herring <robh at kernel.org> wrote:
>>>>>>>
>>>>>>> On Fri, Feb 2, 2018 at 2:01 AM, Tomasz Figa <tfiga at chromium.org>
>>>>>>> wrote:
>>>>>>>>
>>>>>>>> Hi Rob,
>>>>>>>>
>>>>>>>> On Tue, Jan 30, 2018 at 9:36 PM, Robert Foss
>>>>>>>> <robert.foss at collabora.com> wrote:
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>        uint32_t (*get_fd)(buffer_handle_t handle, uint32_t
>>>>>>>>>>>>>> plane);
>>>>>>>>>>>>>>        uint64_t (*get_modifier)(buffer_handle_t handle,
>>>>>>>>>>>>>> uint32_t
>>>>>>>>>>>>>> plane);
>>>>>>>>>>>>>>        uint32_t (*get_offsets)(buffer_handle_t handle, uint32_t
>>>>>>>>>>>>>> plane);
>>>>>>>>>>>>>>        uint32_t (*get_stride)(buffer_handle_t handle, uint32_t
>>>>>>>>>>>>>> plane);
>>>>>>>>>>>>>>        ...
>>>>>>>>>>>>>> } gralloc_funcs_t;
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> These ones? >
>>>>>>>>>> Yeah, if we could retrieve such function pointer struct using
>>>>>>>>>> perform
>>>>>>>>>> or any equivalent (like the implementation-specific methods in
>>>>>>>>>> gralloc1, but not sure if that's going to be used in practice
>>>>>>>>>> anywhere), it could work for us.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> So this is where you and Rob Herring lose me, I don't think I
>>>>>>>>> understand
>>>>>>>>> quite how the gralloc1 call would be used, and how it would tie into
>>>>>>>>> this
>>>>>>>>> handle struct. I think I could do with some guidance on this.
>>>>>>>>
>>>>>>>>
>>>>>>>> This would be very similar to gralloc0 perform call. gralloc1
>>>>>>>> implementations need to provide getFunction() callback [1], which
>>>>>>>> returns a pointer to given function. The list of standard functions
>>>>>>>> is
>>>>>>>> defined in the gralloc1.h header [2], but we could take some random
>>>>>>>> big number and use it for our function that fills in provided
>>>>>>>> gralloc_funcs_t struct with necessary pointers.
>>>>>>>>
>>>>>>>> [1]
>>>>>>>> https://android.googlesource.com/platform/hardware/libhardware/+/master/include/hardware/gralloc1.h#300
>>>>>>>> [2]
>>>>>>>> https://android.googlesource.com/platform/hardware/libhardware/+/master/include/hardware/gralloc1.h#134
>>>>>>>
>>>>>>>
>>>>>>> This is a deadend because it won't work with a HIDL based
>>>>>>> implementation (aka gralloc 2.0). You can't set function pointers (or
>>>>>>> any pointers) because gralloc runs in a different process. Yes,
>>>>>>> currently gralloc is a pass-thru HAL, but AIUI that will go away.
>>>>>>
>>>>>>
>>>>>> Part of it. I can't see IMapper being implemented by a separate
>>>>>> process. You can't map a buffer into one process from another process.
>>>>>>
>>>>>> But anyway, it's a good point, thanks, I almost forgot about its
>>>>>> existence. I'll do further investigation.
>>>>>
>>>>>
>>>>> Okay, so IMapper indeed breaks the approach I suggested. I'm not sure
>>>>> at the moment what we could do about it. (The idea of a dynamic
>>>>> library of a pre-defined name, exporting functions we specify, might
>>>>> still work, though.)
>>>>>
>>>>> Note that the DRM_GRALLOC_GET_FD used currently by Mesa will also be
>>>>> impossible to implement with IAllocator/IMapper. (Although I still
>>>>> think Mesa and Gralloc are free to have separate logic for choosing
>>>>> the DRM device to use.)
>>>>
>>>>
>>>> I think the need for GET_FD goes away when the render node is used. We
>>>> may still need the card node for s/w rendering (if I can ever get that
>>>> working) though. Of course, if we use the vgem approach like CrOS then
>>>> we wouldn't.
>>>
>>>
>>> Hmm, if so, then we probably wouldn't have any strict need for these
>>> function pointers anymore. We already have a makeshift format resolve
>>> in place and the only missing bits that we still need to patch up
>>> downstream are removing GET_FD, dropping drm_gralloc.h and adding a
>>> fallback to kms_swrast if hw driver loading fails.
>>
>>
>> So this discussion is slightly unrelated, but it is where me looking at this
>> started.
>>
>> So I've got a kms_swrast fallback series[1], that I've been wanting to test
>> before trying to push upstream, but haven't been able to run it in the
>> Android environment and the arc++ + chromiumos has also been problematic for
>> various reasons (which are being looked into).
>>
>> Tomasz: If you're interested in testing the series, it would be helpful.
>> Hopefully testing is everything that needed for upstreaming.
>>
>> [1] https://gitlab.collabora.com/robertfoss/mesa/commits/kms_swrast
>

I checked the branch, but it isn't possible to test it directly with
Chrome OS, since we do not provide DRM_GRALLOC_GET_FD functionality
and adding support for probing devices changes the code introduced by
your patches significantly, which kind of defeats the purpose.

I think it might make sense to actually remove the requirement for
DRM_GRALLOC_GET_FD from upstream first (as in my original attempt from
long time ago) and then add kms_swrast fallback on top of that.

Best regards,
Tomasz