Hi Arnd, On Mon, Nov 15, 2021 at 01:38:07PM +0100, Arnd Bergmann wrote: > On Mon, Nov 15, 2021 at 12:49 PM Laurent Pinchart wrote: > > On Mon, Nov 15, 2021 at 11:21:30AM +0100, Arnd Bergmann wrote: > > > On Mon, Nov 15, 2021 at 10:14 AM Laurent Pinchart wrote: > > > > On Mon, Nov 15, 2021 at 09:54:00AM +0100, Arnd Bergmann wrote: > > > > > @@ -1285,11 +1287,13 @@ static int xilinx_dpdma_config(struct dma_chan *dchan, > > > > > spin_lock_irqsave(&chan->lock, flags); > > > > > > > > > > /* > > > > > - * Abuse the slave_id to indicate that the channel is part of a video > > > > > - * group. > > > > > + * Abuse the peripheral_config to indicate that the channel is part > > > > > > > > Is it still an abuse, or is this now the right way to pass custom data > > > > to the DMA engine driver ? > > > > > > It doesn't make the driver any more portable, but it's now being > > > more explicit about it. As far as I can tell, this is the best way > > > to pass data that cannot be expressed through the regular interfaces > > > in DT and the dmaengine API. > > > > > > Ideally there would be a generic way to pass this flag, but I couldn't > > > figure out what this is actually doing, or whether there is a better > > > way. Maybe Vinod has an idea. > > > > I don't think we need a generic API in this case. The DMA engine is > > specific to the display device, I don't foresee a need to mix-n-match. > > Right. I wonder if there is even a point in using the dmaengine API > in that case, I think for other single-purpose drivers we tend to just > integrate the functionality in the client driver. No point changing this > now of course, but it does feel odd. I agree, and that's what I would have done as well, if it wasn't for the fact that the DMA engine also supports a second client for audio. This isn't supported in upstream yet. We could still have created an ad-hoc solution, possibly based on the components framework, but the DMA engine subsystem wasn't a bad fit. > From my earlier reading of the driver, my impression was that this > is just a memory-to-memory device, so it could be used that way > as well, but does need a flag when working on the video memory. > I couldn't quite make sense of that though. It's only memory-to-device (video and audio). See figures 33-1 and 33-16 in https://www.xilinx.com/support/documentation/user_guides/ug1085-zynq-ultrascale-trm.pdf > > > /* > > > * Use the peripheral_config to indicate that the channel is part > > > * of a video group. This requires matching use of the custom > > > * structure in each driver. > > > */ > > > pconfig = config->peripheral_config; > > > if (WARN_ON(config->peripheral_size != 0 && > > > config->peripheral_size != sizeof(*pconfig))) > > > return -EINVAL; > > > > How about > > > > if (WARN_ON(config->peripheral_config && > > config->peripheral_size != sizeof(*pconfig))) > > > > > > > > spin_lock_irqsave(&chan->lock, flags); > > > if (chan->id <= ZYNQMP_DPDMA_VIDEO2 && > > > config->peripheral_size == sizeof(*pconfig)) > > > > And here you can test pconfig != NULL. > > Good idea. Changed now, using 'if (pconfig)' without the '!= NULL' > in both expressions. Sounds good to me. -- Regards, Laurent Pinchart
