linux-kernel - Re: [PATCH 3/6] ARM: Add Krait L2 accessor functions

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Message-ID: <20131029013230.GI4763@kartoffel>
Date:	Mon, 28 Oct 2013 18:32:31 -0700
From:	Mark Rutland <mark.rutland@....com>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	"linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	Russell King <linux@....linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3/6] ARM: Add Krait L2 accessor functions

On Tue, Oct 29, 2013 at 01:21:57AM +0000, Stephen Boyd wrote:
> On 10/28/13 18:19, Mark Rutland wrote:
> > On Tue, Oct 29, 2013 at 12:31:27AM +0000, Stephen Boyd wrote:
> >> Qualcomm's Krait CPUs have a handful of L2 cache controller
> >> registers that live behind a cp15 based indirection register.
> >> First you program the indirection register (l2cpselr) to point
> >> the L2 'window' register (l2cpdr) at what you want to read/write.
> >> Then you read/write the 'window' register to do what you want.
> >> The l2cpselr register is not banked per-cpu so we must lock
> >> around accesses to it to prevent other CPUs from re-pointing
> >> l2cpdr underneath us.
> >>
> >> Cc: Russell King <linux@....linux.org.uk>
> >> Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
> >> ---
> >>  arch/arm/common/Kconfig                   |  3 ++
> >>  arch/arm/common/Makefile                  |  1 +
> >>  arch/arm/common/krait-l2-accessors.c      | 52 +++++++++++++++++++++++++++++++
> >>  arch/arm/include/asm/krait-l2-accessors.h | 20 ++++++++++++
> >>  4 files changed, 76 insertions(+)
> >>  create mode 100644 arch/arm/common/krait-l2-accessors.c
> >>  create mode 100644 arch/arm/include/asm/krait-l2-accessors.h
> > [...]
> >
> >> +void set_l2_indirect_reg(u32 addr, u32 val)
> >> +{
> >> +	unsigned long flags;
> >> +
> >> +	raw_spin_lock_irqsave(&krait_l2_lock, flags);
> >> +
> >> +	asm volatile ("mcr p15, 3, %0, c15, c0, 6" : : "r" (addr));
> >> +	isb();
> >> +	asm volatile ("mcr p15, 3, %0, c15, c0, 7" : : "r" (val));
> >> +	isb();
> >> +
> >> +	raw_spin_unlock_irqrestore(&krait_l2_lock, flags);
> >> +}
> >> +EXPORT_SYMBOL(set_l2_indirect_reg);
> > It might be worth commmenting inline as to what register each of these is
> > accessing. Inevitably the commit message will become harder to find and
> > associate with the code over time.
> >
> > Similarly for get_l2_indirect_reg.
> 
> Do you mean with the "@" syntax in the assembly? The 80-character limit
> is out to get me.

I probably didn't mean inline :)

How about a block comment above the first asm block like:

/*
 * Select the L2 window by poking l2cpselr, then write to the window via
 * l2cpdr.
 */

Thanks,
Mark.
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