On Monday, August 08, 2011 10:01:19 AM Albert ARIBAUD wrote:
> Hi Hong Xu,
>
> Le 08/08/2011 05:20, Hong Xu a écrit :
> > After DMA operation, we need to maintain D-Cache coherency.
> > So that the DCache must be invalidated (hence CPU will fetch
> > data written by DMA controller from RAM).
> >
> > Tested on AT91SAM9261EK with Peripheral DMA controller.
> >
> > Signed-off-by: Hong Xu<hong...@atmel.com>
> > Tested-by: Elen Song<elen.s...@atmel.com>
> > CC: Albert Aribaud<albert.u.b...@aribaud.net>
> > CC: Aneesh V<ane...@ti.com>
> > CC: Reinhard Meyer<u-b...@emk-elektronik.de>
> > CC: Heiko Schocher<h...@denx.de>
> > ---
> >
> > V2:
> > Per Albert's suggestion, add invalidate_dcache_range
> >
> > V3:
> > invalidate_dcache_range emits warning when detecting unaligned buffer
> >
> > invalidate_dcache_range won't clean any adjacent cache line when
> > detecting unaligned buffer and only round up/down the buffer address
> >
> > + mva = start;
> > + if ((mva& (cache_line_len - 1)) != 0) {
> > + printf("WARNING: %s - unaligned buffer detected, starting "
>
> I'd rather have a message about "cache", not "buffer", e.g.
>
> printf("WARNING: %s - start address %x is not aligned\n"
> __FUNCTION__, start);
__func__ is prefered in linux kernel :-)
>
> > + mva&= ~(cache_line_len - 1);
> > + }
> > + if ((stop& (cache_line_len - 1)) != 0) {
> > + printf("WARNING: %s - unaligned buffer detected, ending "
> > + "address: 0x%08x\n", __FUNCTION__, stop);
>
> Ditto.
Ditto.
>
> > + stop = (stop | (cache_line_len - 1)) + 1;
> > + }
> > +
> > + while (mva< stop) {
> > + asm("mcr p15, 0, %0, c7, c6, 1" : : "r"(mva));
> > + mva += cache_line_len;
> > + }
>
> Thinking more about the degenerate case -- why not round *up* the start
> address, and round *down* the stop address, that is, *reduce* the area
> to the aligned portion rather than *expand* it into the unknown? That
> would make data in "partially owned" cache lines safe from unwanted
> invalidation. OTOH, it would not completely invalidate the caller's
> data, but at least the malfunction would appear in the faulty calling
> code, not elsewhere.
That'd introduce even stranger behaviour and it'd be even more sickening to
debug
>
> Opinions?
>
> Amicalement,
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