linux-kernel - Re: [PATCHv4 1/2] ARM: imx53: add secure-reg-access support for PMU

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Date:   Mon, 28 May 2018 17:50:42 +0200
From:   Sebastian Reichel <sebastian.reichel@...labora.co.uk>
To:     Shawn Guo <shawnguo@...nel.org>
Cc:     Sascha Hauer <kernel@...gutronix.de>,
        Fabio Estevam <fabio.estevam@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>, Ian Ray <ian.ray@...com>,
        Nandor Han <nandor.han@...com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel@...labora.com
Subject: Re: [PATCHv4 1/2] ARM: imx53: add secure-reg-access support for PMU

Hi,

On Mon, May 28, 2018 at 03:20:35PM +0800, Shawn Guo wrote:
> On Mon, May 28, 2018 at 08:41:31AM +0200, Sebastian Reichel wrote:
> > > Are you saying this is a very specific setup required by i.MX53 only?
> > 
> > Yes, all other SoCs supported by Linux ARM PMU counters driver can
> > just use the registers without having to enable platform specific
> > bits first.
> > 
> > > In that case, I can live with it.
> > 
> > What about the DT node? I did not add it, since this is a i.MX53
> > specific workaround anyways.
> 
> What you are adding here is secure-reg-access property, which has an
> defined meaning in PMU binding doc.  I'm not really sure if it's
> appropriate to use the property as a condition for DBGEN bit setup.
> Or can we set up the bit regardless of the property?

The description for DBGEN bit is:

> Debug enable. This allows the user to manually activate clocks
> within the debug system. This register bit directly controls the
> platform's dbgen_out output signal which connects to the DAP_SYS to
> enable all debug clocks. Once enabled, the clocks cannot be disabled
> except by asserting the disable_trace input of the DAP_SYS.

I only enable this bit when the kernel configuration allows
using the PMU, since otherwise we do not need the clocks
in the debug system. This limits any potential side-effects
of this patchset.

-- Sebastian

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