Messages in this thread | | | Date | Thu, 15 Feb 2024 11:36:35 +0000 | Subject | Re: [PATCH net-next v3 2/7] dma: avoid redundant calls for sync operations | From | Robin Murphy <> |
| |
On 15/02/2024 5:08 am, Christoph Hellwig wrote: > On Wed, Feb 14, 2024 at 05:55:23PM +0000, Robin Murphy wrote: >>> #define DMA_F_PCI_P2PDMA_SUPPORTED (1 << 0) >>> +#define DMA_F_CAN_SKIP_SYNC BIT(1) >> >> Yuck, please be consistent - either match the style of the existing code, >> or change that to BIT(0) as well. > > Just don't use BIT() ever. It doesn't save any typing and creates a > totally pointless mental indirection. > >> I guess this was the existing condition from dma_need_sync(), but now it's >> on a one-off slow path it might be nice to check the sync_sg_* ops as well >> for completeness, or at least comment that nobody should be implementing >> those without also implementing the sync_single_* ops. > > Implementing only one and not the other doesn't make any sense. Maybe > a debug check for that is ok, but thing will break badly if they aren't > in sync anyway.
In principle we *could* have an implementation which used bouncing purely to merge coherent scatterlist segments, thus didn't need to do anything for single mappings. I agree that it wouldn't seem like a particularly realistic thing to do these days, but I don't believe the API rules it out, so it might be nice to enforce that assumption somewhere if we are actually relying on it (although I also concur that this may not necessarily be the ideal place to do that in general).
Thanks, Robin.
| |