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

[Rob Herring]

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.

Rob