Re: [PATCH v7 6/6] drm: exynos: mixer: Add interconnect support

[Krzysztof Kozlowski <krzk@kernel.org>]

On Fri, Oct 30, 2020 at 01:51:49PM +0100, Sylwester Nawrocki wrote:
> This patch adds interconnect support to exynos-mixer. The mixer works
> the same as before when CONFIG_INTERCONNECT is 'n'.
> 
> For proper operation of the video mixer block we need to ensure the
> interconnect busses like DMC or LEFTBUS provide enough bandwidth so
> as to avoid DMA buffer underruns in the mixer block. I.e we need to
> prevent those busses from operating in low perfomance OPPs when
> the mixer is running.
> In this patch the bus bandwidth request is done through the interconnect
> API, the bandwidth value is calculated from selected DRM mode, i.e.
> video plane width, height, refresh rate and pixel format.
> 
> The bandwidth setting is synchronized with VSYNC when we are switching
> to lower bandwidth. This is required to ensure enough bandwidth for
> the device since new settings are normally being applied in the hardware
> synchronously with VSYNC.
> 
> Co-developed-by: Artur Świgoń <a.swigon@samsung.com>
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
> ---
> Changes for v7:
>  - fixed incorrect setting of the ICC bandwidth when the mixer is
>    disabled, now the bandwidth is set explicitly to 0 in such case.
> 
> Changes for v6:
>  - the icc_set_bw() call is now only done when calculated value for
>    a crtc changes, this avoids unnecessary calls per each video frame
>  - added synchronization of the interconnect bandwidth setting with
>    the mixer VSYNC in order to avoid buffer underflow when we lower
>    the interconnect bandwidth when the hardware still operates with
>    previous mode settings that require higher bandwidth. This fixed
>    IOMMU faults observed e.g. during switching from two planes to
>    a single plane operation.
> 
> Changes for v5:
>  - renamed soc_path variable to icc_path
> ---
>  drivers/gpu/drm/exynos/exynos_mixer.c | 146 ++++++++++++++++++++++++++++++++--
>  1 file changed, 138 insertions(+), 8 deletions(-)
> 

Acked-by: Krzysztof Kozlowski <krzk@kernel.org>

Best regards,
Krzysztof