Re: [RFC] tegra_pcm DMA buffers allocation

[Thierry Reding <thierry.reding-RM9K5IK7kjKj5M59NBduVrNAH6kLmebB@public.gmane.org>]

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* Stephen Warren wrote:
> On 04/19/2012 03:07 PM, Andrey Smirnov wrote:
> > On Thu, 2012-04-19 at 16:07 -0400, Stephen Warren wrote:
> ...
> >> BTW, did you try running the mainline code on your board. If it's
> >> derived from Harmony, it should be easy to get it going.
> > 
> > Last time we did there was no support for Tegra's NAND and display
> > controllers
> 
> What do you need the NAND controllers for? I'm not 100% certain, but I
> believe we plan on upstreaming NAND support into U-Boot, but not the
> kernel, since we didn't see a need for it there IIRC.

We use a device that is sort of a set-top box, which currently boots from an
SD card. However the SD card is eventually supposed to allow users to display
custom media (slide show, ...). In that case it is very stupid to keep the OS
on the same card.

While U-Boot NAND support is enough to get a kernel booted, you still need
the root filesystem to be loaded from NAND by the kernel. Kernel support is
also pretty much a requirement for runtime updates.

> (Not that we'd stop anyone else doing it)

I've been trying to make the NAND controller work on Tegra 2. Unfortunately
there's not much of a reference to work off except the driver that Simon
Glass posted to the U-Boot mailing list and written by Jim Lin. There is also
a driver in the NVIDIA downstream kernels but that's pretty much broken.

The U-Boot driver doesn't use interrupts obviously so I've resolved to use it
as a base and add interrupt support. Unfortunately I've hit a snag and
whenever I enable interrupts I see the CPU stormed by the NAND controller for
unknown reasons (no bits in ISR, DMA control or decode status registers set).
I'll have to investigate further. Maybe the controller isn't properly
initialized yet.

Thierry

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