[U-Boot-Users] [PATCH] USB: shutdown USB before booting

[Stefan Roese <sr@denx.de>]

Hi Markus,

On Thursday 10 July 2008, Markus Klotzb?cher wrote:
> This patch fixes a potentially serious issue related to USB which was
> discouvered by Martin Krause <martin.krause@tqs.de> and fixed for
> ARM920T. Martin wrote:
>
>   Turn off USB to prevent the host controller from writing to the
>   SDRAM while Linux is booting. This could happen, because the HCCA
>   (Host Controller Communication Area) lies within the SDRAM and the
>   host controller writes continously to this area (as busmaster!), for
>   example to increase the HccaFrameNumber variable, which happens
>   every 1 ms.
>
> This is a slightly modified version of the patch in order to shutdown
> USB when booting on all architectures.

Yes, I remember hearing of this problem. I thought it was already fixed. Seems 
not to be the case. Please find a comment below.

> Signed-off-by: Markus Klotzbuecher <mk@denx.de>
> ---
>  common/cmd_bootm.c |   18 ++++++++++++++++++
>  1 files changed, 18 insertions(+), 0 deletions(-)
>
> diff --git a/common/cmd_bootm.c b/common/cmd_bootm.c

By implementing this usb_stop() in do_bootm() you prevent this problem in many 
cases (e.g. Linux booting). But unfortunately not in all cases. For 
example "bootelf" or "bootvx" are not fixed.

Can't this be solved in a different way. By calling usb_stop each time after 
an USB command completes. IIRC, this is how it is done in the U-Boot network 
implementation too.

What do you think?

Best regards,
Stefan

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