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

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Date:   Mon, 26 Feb 2018 14:47:41 +0100
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 Shawn,

On Sat, Feb 24, 2018 at 03:45:44PM +0800, Shawn Guo wrote:
> On Mon, Feb 12, 2018 at 01:39:44PM +0100, Sebastian Reichel wrote:
> > On i.MX53 it is necessary to set the DBG_EN bit in the
> > platform GPC register to enable access to PMU counters
> > other than the cycle counter.
> > 
> > Signed-off-by: Sebastian Reichel <sebastian.reichel@...labora.co.uk>
> > ---
> >  arch/arm/mach-imx/mach-imx53.c | 39 ++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 38 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm/mach-imx/mach-imx53.c b/arch/arm/mach-imx/mach-imx53.c
> > index 07c2e8dca494..658e28604dca 100644
> > --- a/arch/arm/mach-imx/mach-imx53.c
> > +++ b/arch/arm/mach-imx/mach-imx53.c
> > @@ -28,10 +28,47 @@ static void __init imx53_init_early(void)
> >  	mxc_set_cpu_type(MXC_CPU_MX53);
> >  }
> >  
> > +#define MXC_CORTEXA8_PLAT_GPC 0x63fa0004
> 
> The base address should be retrieved from device tree.

DT has no entry for 0x63fa0000-0x63fa3fff. iMX53 TRM lists it as "ARM Platform"
with 8 platform specific 32 bit registers. Do you think it's worth the trouble
adding a new binding? Do you have a suggestion for a compatible value?

-- Sebastian

> 
> Shawn
> 
> > +#define GPC_DBG_EN BIT(16)
> > +
> > +/*
> > + * This enables the DBGEN bit in ARM_GPC register, which is
> > + * required for accessing some performance counter features.
> > + * Technically it is only required while perf is used, but to
> > + * keep the source code simple we just enable it all the time
> > + * when the kernel configuration allows using the feature.
> > + */
> > +static void imx53_pmu_init(void)
> > +{
> > +	void __iomem *gpc_reg;
> > +	struct device_node *node;
> > +	u32 gpc;
> > +
> > +	if (!IS_ENABLED(CONFIG_ARM_PMU))
> > +		return;
> > +
> > +	node = of_find_compatible_node(NULL, NULL, "arm,cortex-a8-pmu");
> > +	if (!node)
> > +		return;
> > +
> > +	if (!of_property_read_bool(node, "secure-reg-access"))
> > +		return;
> > +
> > +	gpc_reg = ioremap(MXC_CORTEXA8_PLAT_GPC, 4);
> > +	if (!gpc_reg) {
> > +		pr_warning("unable to map GPC to enable perf\n");
> > +		return;
> > +	}
> > +
> > +	gpc = readl_relaxed(gpc_reg);
> > +	gpc |= GPC_DBG_EN;
> > +	writel_relaxed(gpc, gpc_reg);
> > +}
> > +
> >  static void __init imx53_dt_init(void)
> >  {
> >  	imx_src_init();
> > -
> > +	imx53_pmu_init();
> >  	imx_aips_allow_unprivileged_access("fsl,imx53-aipstz");
> >  }
> >  
> > -- 
> > 2.15.1
> > 

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