ARM: hw_breakpoint: silent EPERM when setting ARM_DSCR_MDBGEN on ARM_DEBUG_ARCH_V7_ECP14

On 09/10/12 18:05, Valentin Pistol wrote:

Will,

On Tue, Sep 18, 2012 at 3:04 AM, Will Deacon [off-list ref] wrote:

quoted

On Fri, Sep 14, 2012 at 09:08:24AM +0100, Valentin Pistol wrote:

quoted

Is there a reliable way to determine that they are locked down?
Any particular register/bit I can check to confirm?

You can take a look at the DBGAUTHSTATUS register and try to determine the
signal values for SPNIDEN, DBGEN and NIDEN.

DBGAUTHSTATUS=0xaa confirming DBGEN is LOW. Since then I found out
that there are two types of OMAP devices:
GP (General Purpose) and HS (High Security) and supposedly Debug
Capabilities are only available on GP devices.
Thus, I ordered a Pandaboard ES with OMAP4460 and tested it with a
prebuilt Ubuntu 12.04 image.
After boot monitor mode is still not set, the DSCR reads the same
0x01030002 just as with the previous Galaxy Nexus.

I contacted TI and they seem to say hw breakpoints/watchpoints are
available on Pandaboard but they are confused about monitor mode,
saying it's not available on Pandaboard GP.
See http://e2e.ti.com/support/omap/f/849/p/216276/770995.aspx for the
discussion.
Isn't monitor mode and DBGEN on HIGH required for access to
breakpoints/watchpoints?
Maybe they are thinking about Secure Monitor Mode and TrustZone which
is not related?

Have you used a Pandaboard and can comment on how to enable the
breakpoints/watchpoints?
Could you also mention a specific development board that you are using
and recommend for access to these features?

I'm running Linaro 12.08 on Pandaboard (Rev A1) and on this board 
DBGAUTHSTATUS.NSNE and DBGAUTHSTATUS.NSE are set.

With additional logs in enable_monitor_mode() 
[arch/arm/kernel/hw_breakpoint.c]:

root at linaro-nano:~# dmesg | grep hw-break
[    0.321380] hw-breakpoint: arch_hw_breakpoint_init cpu0 debug_arch=3
[    0.321441] hw-breakpoint: enable_monitor_mode cpu1 
DBGDSCR=03070002
[    0.321441] hw-breakpoint: enable_monitor_mode cpu1 
DBGAUTHSTATUS=000000af
[    0.321502] hw-breakpoint: enable_monitor_mode cpu0 
DBGDSCR=03070002
[    0.321533] hw-breakpoint: enable_monitor_mode cpu0 
DBGAUTHSTATUS=000000af
[    0.321533] hw-breakpoint: found 5 (+1 reserved) breakpoint and 1 
watchpoint registers.
[    0.321563] hw-breakpoint: maximum watchpoint size is 4 bytes.

-- Dietmar

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Completely untested patch below, please let me know how you get on...

Looks good, I'll give it a try.

Great. Let me know if it helps and, if so, I'll merge it.

Sorry I wasn't able to directly apply your patch to the specific
Android kernel version I was using.
Manually merging the code seems to perform as expected.

Thanks a lot for your help,
Valentin

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