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

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Date:   Tue, 29 Aug 2023 14:16:31 -0700
From:   Yabin Cui <yabinc@...gle.com>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     Mike Leach <mike.leach@...aro.org>,
        James Clark <james.clark@....com>,
        Leo Yan <leo.yan@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] coresight: tmc-etr: Don't fail probe when non-secure
 access is disabled

> 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@....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@...gle.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);
>