lkml.org 
[lkml]   [2012]   [Sep]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] ARM: hw_breakpoint: Clear breakpoints before enabling monitor mode
Hi Stephen,

On Thu, Sep 20, 2012 at 05:57:40PM +0100, Stephen Boyd wrote:
> The reset value of the BCR, BVR, WCR, and WVR registers are all
> UNKNOWN on ARMv7. Unfortunately, reset_ctrl_regs() clears these
> registers *after* enabling monitor mode, not before, and so some
> implementations may experience UNPREDICTABLE behavior if the
> reset values of these registers are non-zero. Clear the
> breakpoints before enabling monitor mode so that we don't
> experience boot hangs/loops due to breakpoints being enabled
> out of reset.
>
> Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>

Aha, thanks for the patch. We should definitely zero these registers before
enabling monitor mode. However...

> +/* Determine if halting mode is enabled */
> +static int halting_mode_enabled(void)
> +{
> + u32 dscr;
> +
> + ARM_DBG_READ(c1, 0, dscr);
> +
> + if (WARN_ONCE(dscr & ARM_DSCR_HDBGEN,
> + "halting debug mode enabled. Unable to access hardware resources.\n")) {
> + return -EPERM;
> + }
> + return 0;
> +}

...it looks like debug arch 7.1 defines this bit as UNKNOWN when the OS lock
is clear, so we probably shouldn't be reading it at all. I'll pour myself a
stiff drink and start reading the debug arch docs to work out what on Earth
we should do.

Stay tuned.

Will


\
 
 \ /
  Last update: 2012-09-20 20:21    [W:0.102 / U:0.172 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site