linux-kernel - Re: [PATCH] [v1] arch: arm: configs: gxp

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Message-ID: <7F9A8F8A-6CA9-4DDC-A564-4E4CB677089F@hpe.com>
Date:   Fri, 18 Mar 2022 21:53:59 +0000
From:   "Verdun, Jean-Marie" <verdun@....com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     "Hawkins, Nick" <nick.hawkins@....com>,
        Russell King <linux@...linux.org.uk>,
        Joel Stanley <joel@....id.au>,
        Andrew Jeffery <andrew@...id.au>,
        Olof Johansson <olof@...om.net>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [v1] arch: arm: configs: gxp_defconfig

Hi Arnd,

>    I'm not familiar with the hw_breakpoint.c code, but I can see that the
>    get_debug_arch()
>    and core_has_os_save_restore() functions are at least eight years old,
>    and Cortex-A9
>    is one of the most common CPU cores, so it would be unlikely that this
>    is a problem
>    with the CPU core in general. My best guess would be that your boot
>    loader code is
>    missing a bit of initialization that is required to put this into the
>    correct state.

I kept digging, and there is an ARM errata https://developer.arm.com/documentation/uan0009/d/ (764319) which is heading into the direction of the issue we face. The challenge is that the DBGSWENABLE signal is not accessible through software (I am still digging to confirm that), it has to be switched from the external debugger. What is weird is that many vendors are referring this errata, they shall be facing the same kind of challenges in some way.

vejmarie