Re: [PATCH net-next 1/7] dma: compile-out DMA sync op calls when not used

[Alexander Lobakin]

From: Christoph Hellwig <hch@xxxxxx>
Date: Mon, 29 Jan 2024 07:11:36 +0100

> On Fri, Jan 26, 2024 at 02:54:50PM +0100, Alexander Lobakin wrote:
>> Some platforms do have DMA, but DMA there is always direct and coherent.
>> Currently, even on such platforms DMA sync operations are compiled and
>> called.
>> Add a new hidden Kconfig symbol, DMA_NEED_SYNC, and set it only when
>> either sync operations are needed or there is DMA ops or swiotlb
>> enabled. Set dma_need_sync() and dma_skip_sync() (stub for now)
>> depending on this symbol state and don't call sync ops when
>> dma_skip_sync() is true.
>> The change allows for future optimizations of DMA sync calls depending
>> on compile-time or runtime conditions.
> 
> So the idea of compiling out the calls sounds fine to me.  But what
> is the point of the extra indirection through the __-prefixed calls?

Because dma_sync_* ops are external functions, not inlines, and in the
next patch I'm adding a check there.

> 
> And if we need that (please document it in the commit log), please
> make the wrappers proper inline functions and not macros.

Thanks,
Olek