[U-Boot] [PATCH] spi: Tegra2: Seaboard: fix UART corruption during SPI transactions

[Simon Glass]

Hi Tom,

On Mon, May 14, 2012 at 10:26 AM, Tom Warren <twarren.nvidia at gmail.com>wrote:

> Simon,
>
> On Fri, May 11, 2012 at 5:16 PM, Simon Glass <sjg at chromium.org> wrote:
> > Hi Tom,
> >
> > On Fri, May 11, 2012 at 1:14 PM, jimmzhang <jimmzhang at nvidia.com> wrote:
> >>
> >> On Wed, 2012-05-09 at 10:34 -0700, Tom Warren wrote:
> >> > Simon Glass's proposal to fix this on Seaboard was NAK'd, so I
> >> > removed his NS16550 references and added a small delay before
> >> > SPI/UART muxing. Tested on my Seaboard with large SPI reads/writes
> >> > and saw no corruption (crc's matched) and no spurious comm chars.\
> >
> >
> > I'm afraid this version does not work fully for me. The problem is I
> think
> > that the UART gets zero bytes in it from when the SPI was active. This
> > causes the next command to be ignored. So for example:
> >
> > Tegra2 (SeaBoard) # echo fred
> > fred
> > Tegra2 (SeaBoard) # echo edmund
> > edmund
> > Tegra2 (SeaBoard) # saveenv
> > Saving Environment to SPI Flash...
> > Erasing SPI flash...Writing to SPI flash...done
> > Tegra2 (SeaBoard) # echo blackadder
> >
> > ^^^^ this command does nothing!
> >
> > Tegra2 (SeaBoard) # echo blackadder
> > blackadder
> > Tegra2 (SeaBoard) #
> >
> > This is the reason why my original patch cleaned out the UART before
> reading
> > further characters. If that logic really in impossible to have in U-Boot
> > then the only option is (after a SPI operation) to read UART output using
> > tstc() and getc() until there is nothing more. Ick.
> I saw the same thing, and debugged it down to a NUL in the input
> buffer. Not sure how it gets there - some combo of GPIO toggle, pinmux
> switch, etc.
> I have a patch to fix it by dropping the NUL in common/main.c's input
> processing switch(), but I haven't posted it because I don't think
> it'll pass muster, being in common code and all.
>
> I can do some more debugging later to see if moving/changing the
> sequence of GPIO/pinmux toggling and the delays around can eliminate
> the NUL, but it's a low priority. I may also post the main.c NUL drop
> just so anyone with a Seaboard && SPI build can apply it to their
> private build if they want and fix the problem.
>
> As it stands, though, this patch does get SPI working on Seaboard,
> which is the only T20 board with this (really) poor UART/SPI design,
> so I'll add it to the next pull request to Albert.
>
>
Yes, this is probably the best we can do without touching the uart code.

Regards,
Simon



> Thanks,
>
> Tom
> >
> > That said, this is an improvement, since it allows SPI to work. So I am
> > going to ack it so we can hopefully get it in there.
> >
> > Acked-by: Simon Glass <sjg at chromium.org>
> >
> >
> >>
> >> >
> >> > Signed-off-by: Tom Warren <twarren at nvidia.com>
> >>
> >> Tested-by: Jimmy Zhang <jimmzhang at nvidia.com>
> >>
> >>
> >>
> >>
> >>
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> >
> >
> > Regards,
> > Simon
> >
>