[PATCH] mxs/dma: Enlarge the CCW descriptor area to 4 pages
marex at denx.de
Tue Sep 4 21:46:39 EDT 2012
Dear Shawn Guo,
> On Tue, Sep 04, 2012 at 06:04:25AM +0200, Marek Vasut wrote:
> > In case of a large SPI flash, the amount of DMA descriptors
> > available to the DMA driver is not large enough anymore. For
> > example 8MB SPI flash now needs 129 descriptors to be transfered
> > in one long read. There are currently 53 descriptors available in
> > one PAGE_SIZE-big block. Enlarge the allocated descriptor area to
> > four PAGE_SIZE blocks to fulfill such requirements.
> > Signed-off-by: Marek Vasut <marex at denx.de>
> > Cc: Dan Williams <djbw at fb.com>
> > Cc: Fabio Estevam <fabio.estevam at freescale.com>
> > Cc: Shawn Guo <shawn.guo at linaro.org>
> Acked-by: Shawn Guo <shawn.guo at linaro.org>
> Vinod (copied) is the primary maintainer and collecting dma patches now.
Let me ask about another thing. If there'll eventually be some device that'd
need even larger transfer (say ... hundreds of megs) we'd end up with trouble
One way to fix this is to recycle descriptors that were already used during the
transfer, but can we really do it fast enough, so the DMA would do it's job at
one end of the descriptor chain and we'd be building the other?
The other (easier) way is to let the device that claims the particular DMA
channel allocate as much descriptors as it might ever need, which I think is
What do you think ?
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