Re: [RFC PATCH 2/4] pio-mapping: Add ARM support for the PIO mapping API

[Catalin Marinas <catalin.marinas@arm.com>]

On Mon, 2010-02-08 at 17:14 +0000, James Bottomley wrote:
> On Mon, 2010-02-08 at 16:10 +0000, Catalin Marinas wrote:
> 
> This API would have to cope with highmem too ... and because of the
> limited mappings available, we can't just map an arbitrary sized buffer
> (especially in atomics where the number of available slots is often only
> two).
> 
> > static inline void *pio_map_range(void *start, size_t size,
> >                                 enum pio_data_direction dir)
> > {
> >       return start;
> > }
> >
> > static inline void pio_unmap_range(void *start, size_t size,
> >                                  enum pio_data_direction dir)
> > {
> > }
> 
> I think really for range PIO, we need helpers to map and unmap a page at
> a time ... sort of like the for_each_sg approach except this time we
> loop over the pages in the range mapping and unmapping a single one.

These were not intended to create any additional mapping, more like the
dma_map_single() functions and only do the necessary flushing.

AFAICT, an HCD driver would call the pio_map_range() once to get the
address of the buffer and than wait for it to be filled in (e.g. via
interrupts). When it is full, it would call pio_unmap_range(). So even
if we do it per page, you still need to map the same amount of memory,
unless we modify the HCD drivers but I don't think this would be very
popular.

Maybe the name choosing is wrong. Would something like pio_begin() and
pio_end() work better for already mapped buffers?

-- 
Catalin