[U-Boot] Cache alignment warnings on Tegra (ARM)

Simon Glass sjg at chromium.org
Tue Sep 18 22:28:32 CEST 2012


On Tue, Sep 18, 2012 at 1:04 PM, Thierry Reding
<thierry.reding at avionic-design.de> wrote:
> On Tue, Sep 18, 2012 at 09:36:18PM +0200, Marek Vasut wrote:
>> Dear Thierry Reding,
>> [...]
>> > > Sure, but after you apply the bounce buffer, you can safely invalidate
>> > > the whole cacheline, so align it up and be done with it.
>> >
>> > That's what I proposed to do last time around but it was NAK'ed.
>> By who?
> I think it was Simon Glass and Mike Frysinger. They NAK'ed it for very
> valid reason, so I'm not complaining.
>> > At the
>> > time I didn't ensure that the buffer was actually big enough, which is
>> > why people didn't like it (data on the stack after the DMA buffer might
>> > be invalidated as well).
>> Correct, thus the bounce buffer.
> I don't think we even need the bounce buffer. All that needs to be done
> is guarantee that the buffers passed to the MMC driver are properly
> aligned and sized.
> Thierry

Perhaps a point to make here is that we really don't want every driver
(or even driver stack) implementing bounce buffers to when it is not a
huge effort to change the code that calls them (typically filesystem
code) to do the right thing. The code will be smaller and more
efficient if the alignment issues are dealt with at source IMO.


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