Re: [PATCH v2 0/3] drm/meson: implement RDMA for AFBC reset on vsync

[Kevin Hilman <khilman@baylibre.com>]

Neil Armstrong <narmstrong@baylibre.com> writes:

> The VPU embeds a "Register DMA" that can write a sequence of registers
> on the VPU AHB bus, either manually or triggered by an internal IRQ
> event like VSYNC or a line input counter.
>
> The initial implementation handles a single channel (over 8), triggered
> by the VSYNC irq and does not handle the RDMA irq.
>
> The RDMA will be usefull to reset and program the AFBC decoder unit
> on each vsync without involving the interrupt handler that can
> be masked for a long period of time, producing display glitches.
>
> For this we use the meson_rdma_writel_sync() which adds the register
> write tuple (VPU register offset and register value) to the RDMA buffer
> and write the value to the HW.
>
> When enabled, the RDMA is enabled to rewritte the same sequence at the
> next VSYNC event, until a new buffer is committed to the OSD plane.
>
> The the Amlogic G12A is switched to RDMA, the Amlogic GXM Decoder
> doesn't need a reset/reprogram at each vsync.
>
> Changes since v1 at [1]:
> - Fixed a regression when AFBC was not used, adding a reset() call for the afbc module
> - Added a define for the RDMA descriptor size
> - Fixed overflow detection

Reviewed-by: Kevin Hilman <khilman@baylibre.com>

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