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

[Rob Herring]

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.

Rob