Re: [PATCH] coresight: tmc-etr: Don't fail probe when non-secure access is disabled

From: Yabin Cui <yabinc@google.com>
To: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Mike Leach <mike.leach@linaro.org>,
	James Clark <james.clark@arm.com>, Leo Yan <leo.yan@linaro.org>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] coresight: tmc-etr: Don't fail probe when non-secure access is disabled
Date: Tue, 29 Aug 2023 14:16:31 -0700	[thread overview]
Message-ID: <CALJ9ZPNQAWCLrK4u+j3vMZmu3TaLUN_Ne+yqetkquU2QS_XQFQ@mail.gmail.com> (raw)
In-Reply-To: <382193a4-4f30-d804-47da-a9c705b6bee5@arm.com>

> How can this be enabled ? Why not enable it before probing the ETR ?
How can a user know if this has been done or not ?

Pixel devices (like Pixel 6, 7) support enabling some debugging features
(including granting non-secure access to ETM/ETR) even on devices with
secure boot. It is only used internally and has strict requirements,
needing to connect to a server to verify identification after booting.
So it can't be established when probing ETR at device boot time.

On Sun, Aug 27, 2023 at 2:37 PM Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
>
> On 26/08/2023 00:39, Yabin Cui wrote:
> > Because the non-secure access can be enabled later on some devices.
>
> How can this be enabled ? Why not enable it before probing the ETR ?
> How can a user know if this has been done or not ? It is asking for
> trouble to continue without this.
>
> Suzuki
>
> >
> > Signed-off-by: Yabin Cui <yabinc@google.com>
> > ---
> >   drivers/hwtracing/coresight/coresight-tmc-core.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-tmc-core.c b/drivers/hwtracing/coresight/coresight-tmc-core.c
> > index c106d142e632..5ebfd12b627b 100644
> > --- a/drivers/hwtracing/coresight/coresight-tmc-core.c
> > +++ b/drivers/hwtracing/coresight/coresight-tmc-core.c
> > @@ -370,7 +370,7 @@ static int tmc_etr_setup_caps(struct device *parent, u32 devid, void *dev_caps)
> >       struct tmc_drvdata *drvdata = dev_get_drvdata(parent);
> >
> >       if (!tmc_etr_has_non_secure_access(drvdata))
> > -             return -EACCES;
> > +             dev_warn(parent, "TMC ETR doesn't have non-secure access\n");
> >
> >       /* Set the unadvertised capabilities */
> >       tmc_etr_init_caps(drvdata, (u32)(unsigned long)dev_caps);
>