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

Tomasz Figa tfiga at chromium.org
Fri Feb 2 14:51:34 UTC 2018

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.

Best regards,

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