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

[Tomasz Figa]

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

+Gurchetan, who I believe is recently taking care of swrast on our side.

Sure, I'd be more than happy to test it on Monday.

Best regards,
Tomasz