Re: [PATCH v3 1/7] swiotlb: make io_tlb_default_mem local to swiotlb.c

[Robin Murphy]

On 27/06/2023 11:24 am, Greg Kroah-Hartman wrote:
> On Tue, Jun 27, 2023 at 11:54:23AM +0200, Petr Tesarik wrote:
> > +/**
> > + * is_swiotlb_active() - check if the software IO TLB is initialized
> > + * @dev:	Device to check, or %NULL for the default IO TLB.
> > + */
> >   bool is_swiotlb_active(struct device *dev)
> >   {
> > -	struct io_tlb_mem *mem = dev->dma_io_tlb_mem;
> > +	struct io_tlb_mem *mem = dev
> > +		? dev->dma_io_tlb_mem
> > +		: &io_tlb_default_mem;
>
> That's impossible to read and maintain over time, sorry.
>
> Please use real "if () else" lines, so that it can be maintained over
> time.

Moreover, it makes for a horrible interface anyway. If there's a need 
for a non-specific "is SWIOTLB present at all?" check unrelated to any 
particular device (which arguably still smells of poking into 
implementation details...), please encapsulate it in its own distinct 
helper like, say, is_swiotlb_present(void).

However, the more I think about it, the more I doubt that logic like 
octeon_pci_setup() can continue to work properly at all if SWIOTLB 
allocation becomes dynamic... :/

Thanks,
Robin.