[U-Boot-Users] [PATCH] USB: shutdown USB before booting
Stefan Roese
sr at denx.de
Thu Jul 10 15:02:14 CEST 2008
Hi Markus,
On Thursday 10 July 2008, Markus Klotzbücher wrote:
> This patch fixes a potentially serious issue related to USB which was
> discouvered by Martin Krause <martin.krause at 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 at 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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