Re: [PATCH 02/20] dma-mapping: provide a generic dma-noncoherent implementation

[Vineet Gupta]

On 05/18/2018 06:23 AM, hch@xxxxxx wrote:
>   Fri, May 18, 2018 at 01:03:46PM +0000, Alexey Brodkin wrote:
> > Note mmc_get_dma_dir() is just "data->flags & MMC_DATA_WRITE ? DMA_TO_DEVICE : DMA_FROM_DEVICE".
> > I.e. if we're preparing for sending data dma_noncoherent_map_sg() will have DMA_TO_DEVICE which
> > is quite OK for passing to dma_noncoherent_sync_sg_for_device() but in case of reading we'll have
> > DMA_FROM_DEVICE which we'll pass to dma_noncoherent_sync_sg_for_device() in dma_noncoherent_map_sg().
> >
> > I'd say this is not entirely correct because IMHO arch_sync_dma_for_cpu() is supposed to only be used
> > in case of DMA_FROM_DEVICE and arch_sync_dma_for_device() only in case of DMA_TO_DEVICE.
> arc overrides the dir paramter of the dma_sync_single_for_device/
> dma_sync_single_for_cpu calls.  My patches dropped that, and I have
> restored that, and audit for the other architectures is pending.

Right, for now lets retain that and do a sweeping audit of @direction - to me it 
seems extraneous (as it did 10 years ago), but I'm not an expert in this are so 
perhaps it is needed for some device / arches and it would be good to understand 
that finally.

> That being said the existing arc code still looks rather odd as it
> didn't do the same thing for the scatterlist versions of the calls.
> I've thrown in a few patches into my new tree to make the sg versions
> make the normal calls, and to clean up the area a bit.

Not calling names or anything here, but it doesn't exist for sg variants, because 
I didn't write that code :-)
It was introduced by your commi:

2016-01-20 052c96dbe33b arc: convert to dma_map_ops

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