[PATCH v6 18/43] media: sun6i-csi: Add capture state using vsync for page flip

[Jernej Škrabec]

Dne petek, 26. avgust 2022 ob 20:32:15 CET je Paul Kocialkowski napisal(a):
> The current implementation requires up to 3 buffers to properly
> implement page flipping without losing frames: one is configured
> before the video stream is started, one just after that and page
> flipping is synchronized to the frame done interrupt. The comment in
> the code mentions that "CSI will lookup the next dma buffer for next
> frame before the current frame done IRQ triggered".
> 
> Based on observations of the CSI unit behavior, it seems that the
> buffer DMA address is sampled when the frame scan begins (in addition
> to starting the stream), which corresponds to the vblank interrupt
> that hits just before the frame-done interrupt of the previous frame.
> 
> As a result, the address configured at the frame done interrupt is not
> actually used for the next frame but for the one after that.
> 
> This proposal changes the page flipping sync point to the vsync
> interrupt, which allows the DMA address to be sampled for the next
> frame instead and allows operating with only two buffers.
> 
> In addition to the change in the sync point, the code is refactored
> to introduce a notion of state that clarifies tracking of the buffers
> with tidy functions.
> 
> Signed-off-by: Paul Kocialkowski <paul.kocialkowski at bootlin.com>

Acked-by: Jernej Skrabec <jernej.skrabec at gmail.com>

Best regards,
Jernej