[PATCH v2 02/15] drm/panthor: Add uAPI

[Boris Brezillon]

On Wed,  9 Aug 2023 18:53:15 +0200
Boris Brezillon <boris.brezillon at collabora.com> wrote:

> +/**
> + * DOC: MMIO regions exposed to userspace.
> + *
> + * .. c:macro:: DRM_PANTHOR_USER_MMIO_OFFSET
> + *
> + * File offset for all MMIO regions being exposed to userspace. Don't use
> + * this value directly, use DRM_PANTHOR_USER_<name>_OFFSET values instead.
> + *
> + * .. c:macro:: DRM_PANTHOR_USER_FLUSH_ID_MMIO_OFFSET
> + *
> + * File offset for the LATEST_FLUSH_ID register. The Userspace driver controls
> + * GPU cache flushling through CS instructions, but the flush reduction
> + * mechanism requires a flush_id. This flush_id could be queried with an
> + * ioctl, but Arm provides a well-isolated register page containing only this
> + * read-only register, so let's expose this page through a static mmap offset
> + * and allow direct mapping of this MMIO region so we can avoid the
> + * user <-> kernel round-trip.
> + */
> +#define DRM_PANTHOR_USER_MMIO_OFFSET		(0x1ull << 56)

I'm playing with a 32-bit kernel/userspace, and this is problematic,
because vm_pgoff is limited to 32-bit there, meaning we can only map up
to (1ull << (PAGE_SHIFT + 32)) - 1. Should we add a DEV_QUERY to let
userspace set the mmio range?

> +#define DRM_PANTHOR_USER_FLUSH_ID_MMIO_OFFSET	(DRM_PANTHOR_USER_MMIO_OFFSET | 0)