Re: [PATCH v7 2/2] drm/lima: driver for ARM Mali4xx GPUs

[Eric Anholt <eric@anholt.net>]

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Qiang Yu <yuq825@gmail.com> writes:

> - Mali 4xx GPUs have two kinds of processors GP and PP. GP is for
>   OpenGL vertex shader processing and PP is for fragment shader
>   processing. Each processor has its own MMU so prcessors work in
>   virtual address space.
> - There's only one GP but multiple PP (max 4 for mali 400 and 8
>   for mali 450) in the same mali 4xx GPU. All PPs are grouped
>   togather to handle a single fragment shader task divided by
>   FB output tiled pixels. Mali 400 user space driver is
>   responsible for assign target tiled pixels to each PP, but mali
>   450 has a HW module called DLBU to dynamically balance each
>   PP's load.
> - User space driver allocate buffer object and map into GPU
>   virtual address space, upload command stream and draw data with
>   CPU mmap of the buffer object, then submit task to GP/PP with
>   a register frame indicating where is the command stream and misc
>   settings.
> - There's no command stream validation/relocation due to each user
>   process has its own GPU virtual address space. GP/PP's MMU switch
>   virtual address space before running two tasks from different
>   user process. Error or evil user space code just get MMU fault
>   or GP/PP error IRQ, then the HW/SW will be recovered.
> - Use GEM+shmem for MM. Currently just alloc and pin memory when
>   gem object creation. GPU vm map of the buffer is also done in
>   the alloc stage in kernel space. We may delay the memory
>   allocation and real GPU vm map to command submission stage in the
>   furture as improvement.
> - Use drm_sched for GPU task schedule. Each OpenGL context should
>   have a lima context object in the kernel to distinguish tasks
>   from different user. drm_sched gets task from each lima context
>   in a fair way.
>
> mesa driver can be found here before upstreamed:
> https://gitlab.freedesktop.org/lima/mesa
>
> v7:
> - remove lima_fence_ops with default value
> - move fence slab create to device probe
> - check pad ioctl args to be zero
> - add comments for user/kernel interface

Thanks for adding the comments!  That helps a lot.  I feel pretty good
about the ABI at this point.

Reviewed-by: Eric Anholt <eric@anholt.net>

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