[U-Boot] [PATCH 2/2] mmc: tegra: invalidate complete cachelines

[Marek Vasut]

Dear Stephen Warren,

> On 11/02/2012 04:10 PM, Marek Vasut wrote:
> > Dear Stephen Warren,
> > 
> >> On 11/02/2012 03:28 PM, Marek Vasut wrote:
> >>> Dear Stephen Warren,
> >>> 
> >>>> On 11/02/2012 02:38 PM, Marek Vasut wrote:
> >> ...
> >> 
> >>>>> Dumb question -- might be unrelated. Does the tegra mmc driver do
> >>>>> DMA? And if so, what happens if you do raw read to unaligned address
> >>>>> (aka. how come you don't need the bounce buffer)?
> >>>> 
> >>>> Yes, it does DMA, I believe. (At least if it doesn't, I have no idea
> >>>> why the driver is flushing caches!)
> >>>> 
> >>>> I guess we only support the use of aligned addresses, so e.g. the
> >>>> following would work:
> >>>> 
> >>>> ext2load mmc 0:1 0x00100000 /file
> >>>> 
> >>>> but the following wouldn't:
> >>>> 
> >>>> ext2load mmc 0:1 0x00100004 /file
> >>>> 
> >>>> which while I suppose it is an artificial restriction, hasn't been an
> >>>> issue in practice.
> >>> 
> >>> Then just enable the bounce buffer and it will work ;-)
> >> 
> >> You suggested that last time, and it made no difference then... In fact,
> >> the config option you mentioned isn't used anywhere in the srouce tree
> >> except adding bouncebuf.o
> > 
> > Bouncebuf.o ?
> 
> common/bouncebuf.c

Ugh, it was applied ...

> >> into the build right now; which config option
> >> do you think I should use?
> > 
> > CONFIG_BOUNCE_BUFFER
> > 
> > It's used on mx28-based boards.
> 
> Ahah, there's much more to it than just defining the config option, and
> grep'ing for the config option doesn't reveal that.
> 
> Defining CONFIG_BOUNCE_BUFFER simply pulls in bouncebuf.o into the
> build. It's then up to the individual MMC/... driver to actually make
> use of the new functions - i.e. explicitly call e.g.
> bounce_buffer_start(). The MXS MMC driver calls these without any ifdef
> CONFIG_BOUNCE_BUFFER, and hence doesn't show up when you grep for that.
> I had assumed that such functionality would be a conditional part of the
> MMC core rather than the individual drivers, hence had missed the usage
> in the MXS driver.

Sorry about that, I didn't know the patch was pulled in so I expected the old 
approach.

> So, that config option plus some changes to the Tegra MMC driver might
> work - I'll take a look. However, making that change will simply hide
> any unaligned buffer and reduce performance, so I'd still prefer to
> require that buffers be aligned in the future where possible.

Best regards,
Marek Vasut