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

[Robert Foss]

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