Re: [PATCH v2 05/15] staging: mmal-vchiq: Use vc-sm-cma to support zero copy

[Stefan Wahren]

Hi Umang,

Am 09.11.23 um 22:02 schrieb Umang Jain:
> From: Dave Stevenson <dave.stevenson@xxxxxxxxxxxxxxx>
>
> With the vc-sm-cma driver we can support zero copy of buffers between
> the kernel and VPU. Add this support to mmal-vchiq.
>
> Signed-off-by: Dave Stevenson <dave.stevenson@xxxxxxxxxxxxxxx>
> Signed-off-by: Umang Jain <umang.jain@xxxxxxxxxxxxxxxx>
> ---
>   .../staging/vc04_services/vchiq-mmal/Kconfig  |  1 +
>   .../vc04_services/vchiq-mmal/mmal-common.h    |  4 +
>   .../vc04_services/vchiq-mmal/mmal-vchiq.c     | 84 +++++++++++++++++--
>   .../vc04_services/vchiq-mmal/mmal-vchiq.h     |  1 +
>   4 files changed, 83 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/staging/vc04_services/vchiq-mmal/Kconfig b/drivers/staging/vc04_services/vchiq-mmal/Kconfig
> index c99525a0bb45..a7c1a7bf516e 100644
> --- a/drivers/staging/vc04_services/vchiq-mmal/Kconfig
> +++ b/drivers/staging/vc04_services/vchiq-mmal/Kconfig
> @@ -1,6 +1,7 @@
>   config BCM2835_VCHIQ_MMAL
>   	tristate "BCM2835 MMAL VCHIQ service"
>   	depends on BCM2835_VCHIQ
> +	select BCM_VC_SM_CMA

i think we need more explanation in the commit message of the relation 
between these both modules.

On the one side BCM_VC_SM_CMA should be a driver, but it's not a driver 
for a specific hardware. It looks like more an extension of VCHIQ MMAL 
or does other (maybe not yet imported) vc04 driver make also use of this.

My question is: is BCM_VC_SM_CMA a real member on the VCHIQ bus and why?

Best regards