Re: [PATCH v2 2/2] media: imx: vdic: Introduce mem2mem VDI deinterlacer driver

[Nicolas Dufresne <nicolas@ndufresne.ca>]

Le lundi 29 juillet 2024 à 04:16 +0200, Marek Vasut a écrit :
> On 7/24/24 6:08 PM, Nicolas Dufresne wrote:
> > Hi Marek,
> 
> Hi,
> 
> > Le mercredi 24 juillet 2024 à 02:19 +0200, Marek Vasut a écrit :
> > > Introduce dedicated memory-to-memory IPUv3 VDI deinterlacer driver.
> > > Currently the IPUv3 can operate VDI in DIRECT mode, from sensor to
> > > memory. This only works for single stream, that is, one input from
> > > one camera is deinterlaced on the fly with a helper buffer in DRAM
> > > and the result is written into memory.
> > > 
> > > The i.MX6Q/QP does support up to four analog cameras via two IPUv3
> > > instances, each containing one VDI deinterlacer block. In order to
> > > deinterlace all four streams from all four analog cameras live, it
> > > is necessary to operate VDI in INDIRECT mode, where the interlaced
> > > streams are written to buffers in memory, and then deinterlaced in
> > > memory using VDI in INDIRECT memory-to-memory mode.
> > 
> > Just a quick design question. Is it possible to chain the deinterlacer and the
> > csc-scaler ?
> 
> I think you could do that.
> 
> > If so, it would be much more efficient if all this could be
> > combined into the existing m2m driver, since you could save a memory rountrip
> > when needing to deinterlace, change the colorspace and possibly scale too.
> 
> The existing PRP/IC driver is similar to what this driver does, yes, but 
> it uses a different DMA path , I believe it is IDMAC->PRP->IC->IDMAC . 
> This driver uses IDMAC->VDI->IC->IDMAC . I am not convinced mixing the 
> two paths into a single driver would be beneficial, but I am reasonably 
> sure it would be very convoluted. Instead, this driver could be extended 
> to do deinterlacing and scaling using the IC if that was needed. I think 
> that would be the cleaner approach.

No strong opinion, in an ideal world all these hacks are removed and we do a
single multi-context / m2m media controller, that let user pick the path they
need for their task. When I look at the hardware documentation, you can do
inline from VDI to IC, and having IC in both drivers duplicates the CSC
handling. If you allow bypassing the VDI, then you have a duplicated driver and
highly confused users. The fact the ipuv3 (internal) drm driver does not have
the VDI already seems because the display controller driver is missing
interlaced video support, but I could be wrong. Same if you want to support IRT
(even though that is not inline, but using a custom memory protocol).

Nicolas