Re: [PATCH v5 03/11] platform/raspberrypi: Add VideoCore shared memory support

[Florian Fainelli]

On 11/12/2026 3:18 AM, Jai Luthra wrote:
> From: Dave Stevenson <dave.stevenson@xxxxxxxxxxxxxxx>
>
> Add support for the vc-sm-cma driver, to enable sharing of contiguous
> CMA memory allocations with the VideoCore VPU on Raspberry Pi. The
> driver allocates CMA-backed buffers, imports external dmabufs, and
> manages their lifetime via VCHIQ messaging to the VPU service, ensuring
> buffers are not released until both the linux userspace and the VPU
> confirm completion.
>
> VC4 can only physically address the lower 1GB of RAM and requires
> buffers to be mapped through specific uncached address aliases
> (0xC0000000). Thus, standard CMA could not be used as it has no
> mechanism to ensure allocations are visible and valid to VideoCore
> firmware, or handle cache flushes as VC4 can't see ARM's cache state.
>
> The vc-sm-cma driver bridges this gap by allocating memory via CMA on
> the ARM side and explicitly importing it into VideoCore via VCHI.
>
> This driver is primarily used by the wrapper V4L2 drivers for codec and
> ISP, where firmware running on VC4 does the actual video and image
> processing, while the linux userspace interacts with standard V4L2
> driver interfaces. For example, the ISP driver populates large
> lens-shading related tables for a particular camera setup, and uses
> vc-sm-cma to share this buffer with VC4.
>
> Signed-off-by: Dave Stevenson <dave.stevenson@xxxxxxxxxxxxxxx>
> Signed-off-by: Dom Cobley <popcornmix@xxxxxxxxx>
> Signed-off-by: Phil Elwell <phil@xxxxxxxxxxxxxxx>
> Signed-off-by: Alexander Winkowski <dereference23@xxxxxxxxxxx>
> Signed-off-by: Kieran Bingham <kieran.bingham@xxxxxxxxxxxxxxxx>
> Signed-off-by: Juerg Haefliger <juerg.haefliger@xxxxxxxxxxxxx>
> [clean-up for mainline and switch to xarray instead of idr]
> Signed-off-by: Jai Luthra <jai.luthra@xxxxxxxxxxxxxxxx>
> ---

Applied to https://github.com/Broadcom/stblinux/commits/drivers/next, 
thanks!
--
Florian