Re: [PATCH] mmc: mmci: Add new VE MMCI variant

Pawel Moll
2012-12-14T17:35:49Z

On Fri, 2012-12-14 at 17:11 +0000, Russell King - ARM Linux wrote:
> On Fri, Dec 14, 2012 at 03:38:46PM +0000, Pawel Moll wrote:
> > The Versatile Express IOFPGA as shipped on VECD 5.0 (bitfiles v108/208
> > and v116/216) contains a modified version of the PL180 MMCI, with
> > PeriphID Configuration value changed to 0x2.
> >
> > This version adds an optional "hardware flow control" feature. When
> > enabled MMC card clock will be automatically disabled when FIFO is
> > about to over/underflow and re-enabled once the host retrieved some
> > data. This makes the controller immune to over/underrun errors caused
> > by big interrupt handling latencies.
>
> Wrong. It doesn't make it "immune", it just makes it less likely to
> occur - you just need a heavier workload to provoke it.

Why do you think so? The MMC clock is cut off when the FIFO gets full,
so there will be no more data received - no overflow is possible.

Paweł