ARM: hw_breakpoint: silent EPERM when setting ARM_DSCR_MDBGEN on ARM_DEBUG_ARCH_V7_ECP14

On Tue, Oct 09, 2012 at 06:05:53PM +0100, Valentin Pistol wrote:

Will,

Hi Valentin,

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.

Can you try this with my hw-breakpoint branch please? I've reworked a fair
amount of code there, so it might at least be more verbose if it fails.

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.

In that discussion, the TI folks are confusing `Monitor-mode Debug' with
`Secure Monitor Mode'. They are two completely different things and (for the
purposes of this discussion), unrelated. You should press them further on
this!

Have you used a Pandaboard and can comment on how to enable the
breakpoints/watchpoints?

I haven't tried it, but I do have a Panda now so I could give it a go when I
get a chance. I suspect there's something related to power-management at
play... for JTAG, you need to hack MLO as described here:

http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.faqs/ka15314.html

maybe something similar is required for self-hosted (monitor mode) debug?

Could you also mention a specific development board that you are using
and recommend for access to these features?

I use the ARM Versatile Express platform, but I think it's probably quite
expensive to get hold of if you don't work for ARM.

Will