RE: [RFC 1/1] swiotlb: Reduce calls to swiotlb_find_pool()

[Michael Kelley <mhklinux@xxxxxxxxxxx>]

From: Petr Tesařík <petr@xxxxxxxxxxx> Sent: Friday, June 28, 2024 12:47 AM
> 
> V Fri, 28 Jun 2024 08:01:29 +0200
> "hch@xxxxxx" <hch@xxxxxx> napsáno:
> 
> > On Thu, Jun 27, 2024 at 04:02:59PM +0000, Michael Kelley wrote:
> > > > > Conceptually, it's still being used as a boolean function based on
> > > > > whether the return value is NULL.  Renaming it to swiotlb_get_pool()
> > > > > more accurately describes the return value, but obscures the
> > > > > intent of determining if it is a swiotlb buffer.  I'll think about it.
> > > > > Suggestions are welcome.
> > > >
> > > > Just keep is_swiotlb_buffer as a trivial inline helper that returns
> > > > bool.
> > >
> > > I don't understand what you are suggesting.  Could you elaborate a bit?
> > > is_swiotlb_buffer() can't be trivial when CONFIG_SWIOTLB_DYNAMIC
> > > is set.
> >
> > Call the main function that finds and retuns the pool swiotlb_find_pool,
> > and then have a is_swiotlb_buffer wrapper that just returns bool.
> >
> 
> I see. That's not my point. After applying Michael's patch, the return
> value is always used, except here:
> 
> bool dma_direct_need_sync(struct device *dev, dma_addr_t dma_addr)
> {
>       return !dev_is_dma_coherent(dev) ||
>              is_swiotlb_buffer(dev, dma_to_phys(dev, dma_addr));
> }
> 
> I don't think this one occurrence in the entire source tree is worth a
> separate inline function.
> 
> If nobody has a better idea, I'm not really offended by keeping the
> original name, is_swiotlb_buffer(). It would just become the only
> function which starts with "is_" and provides more information in the
> return value than a simple yes/no, and I thought there must be an
> unwritten convention about that.
> 

Unless there is further discussion on this point, I'll just keep the original
"is_swiotlb_buffer()" in v2.

Michael