Messages in this thread | | | Date | Mon, 26 Feb 2024 16:27:16 +0000 | Subject | Re: [PATCH net-next v3 1/7] dma: compile-out DMA sync op calls when not used | From | Robin Murphy <> |
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On 19/02/2024 12:53 pm, Alexander Lobakin wrote: > From: Robin Murphy <robin.murphy@arm.com> > Date: Wed, 14 Feb 2024 17:20:50 +0000 > >> On 2024-02-14 4:21 pm, Alexander Lobakin wrote: > > [...] > >>> -static inline void dma_sync_single_for_cpu(struct device *dev, >>> dma_addr_t addr, >>> - size_t size, enum dma_data_direction dir) >>> +static inline void __dma_sync_single_for_cpu(struct device *dev, >>> + dma_addr_t addr, size_t size, enum dma_data_direction dir) >> >> To me it would feel more logical to put all the wrappers inside the >> #ifdef CONFIG_HAS_DMA and not touch these stubs at all (what does it >> mean to skip an inline no-op?). Or in fact, if dma_skip_sync() is >> constant false for !HAS_DMA, then we could also just make the external >> function declarations unconditional and remove the stubs. Not a critical >> matter though, and I defer to whatever Christoph thinks is most >> maintainable. > > It's done like that due to that I'm adding a runtime check in the second > patch. I don't feel like touching this twice makes sense.
Huh? Why would anything need touching twice? All I'm saying is that it's pretty pointless to add any invocations of dma_skip_sync() in !HAS_DMA paths where we already know the whole API is stubbed out anyway. The only cases which are worth differentiating here are HAS_DMA + DMA_NEED_SYNC vs. HAS_DMA + !DMA_NEED_SYNC (with the subsequent runtime check then just subdividing the former).
> > [...] > >>> @@ -348,18 +348,72 @@ static inline void dma_unmap_single_attrs(struct >>> device *dev, dma_addr_t addr, >>> return dma_unmap_page_attrs(dev, addr, size, dir, attrs); >>> } >>> +static inline void __dma_sync_single_range_for_cpu(struct device *dev, >>> + dma_addr_t addr, unsigned long offset, size_t size, >>> + enum dma_data_direction dir) >>> +{ >>> + __dma_sync_single_for_cpu(dev, addr + offset, size, dir); >>> +} >>> + >>> +static inline void __dma_sync_single_range_for_device(struct device >>> *dev, >>> + dma_addr_t addr, unsigned long offset, size_t size, >>> + enum dma_data_direction dir) >>> +{ >>> + __dma_sync_single_for_device(dev, addr + offset, size, dir); >>> +} >> >> There is no need to introduce these two. > > I already replied to this in the previous thread. Some subsys may want > to check for the shortcut earlier to avoid call ladders of their own > functions. See patch 6 for example where I use this one.
Ugh, no. If the page pool code wants to be clever poking around and sidestepping parts of the documented API, it can flippin' well open-code a single addition to call __dma_sync_single_for_device() directly itself. I'm not at all keen on having to maintain "common" APIs for such niche trickery.
Thanks, Robin.
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