linux-kernel - Re: [PATCH 3/3] arm: zynq: slcr: Use read-modify-write for register writes

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Date:	Thu, 18 Jul 2013 08:45:03 -0700
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Steffen Trumtrar <s.trumtrar@...gutronix.de>
CC:	Michal Simek <michal.simek@...inx.com>,
	Russell King <linux@....linux.org.uk>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3/3] arm: zynq: slcr: Use read-modify-write for register
 writes

On Thu, Jul 18, 2013 at 09:21:06AM +0200, Steffen Trumtrar wrote:
> On Wed, Jul 17, 2013 at 10:10:15AM -0700, Sören Brinkmann wrote:
> > zynq_slcr_cpu_start/stop() ignored the current register state when
> > writing to a register. Fixing this by implementing proper
> > read-modify-write.
> > 
> > Signed-off-by: Soren Brinkmann <soren.brinkmann@...inx.com>
> > ---
> >  arch/arm/mach-zynq/slcr.c | 16 ++++++++--------
> >  1 file changed, 8 insertions(+), 8 deletions(-)
> > 
> > diff --git a/arch/arm/mach-zynq/slcr.c b/arch/arm/mach-zynq/slcr.c
> > index 44a4ab6..1836d5a 100644
> > --- a/arch/arm/mach-zynq/slcr.c
> > +++ b/arch/arm/mach-zynq/slcr.c
> > @@ -61,11 +61,11 @@ void zynq_slcr_system_reset(void)
> >   */
> >  void zynq_slcr_cpu_start(int cpu)
> >  {
> > -	/* enable CPUn */
> > -	writel(SLCR_A9_CPU_CLKSTOP << cpu,
> > -	       zynq_slcr_base + SLCR_A9_CPU_RST_CTRL_OFFSET);
> > -	/* enable CLK for CPUn */
> > -	writel(0x0 << cpu, zynq_slcr_base + SLCR_A9_CPU_RST_CTRL_OFFSET);
> > +	u32 reg = readl(zynq_slcr_base + SLCR_A9_CPU_RST_CTRL_OFFSET);
> > +	reg &= ~(SLCR_A9_CPU_RST << cpu);
> > +	writel(reg, zynq_slcr_base + SLCR_A9_CPU_RST_CTRL_OFFSET);
> > +	reg &= ~(SLCR_A9_CPU_CLKSTOP << cpu);
> > +	writel(reg, zynq_slcr_base + SLCR_A9_CPU_RST_CTRL_OFFSET);
> >  }
> >  
> >  /**
> > @@ -74,9 +74,9 @@ void zynq_slcr_cpu_start(int cpu)
> >   */
> >  void zynq_slcr_cpu_stop(int cpu)
> >  {
> > -	/* stop CLK and reset CPUn */
> > -	writel((SLCR_A9_CPU_CLKSTOP | SLCR_A9_CPU_RST) << cpu,
> > -	       zynq_slcr_base + SLCR_A9_CPU_RST_CTRL_OFFSET);
> > +	u32 reg = readl(zynq_slcr_base + SLCR_A9_CPU_RST_CTRL_OFFSET);
> > +	reg |= (SLCR_A9_CPU_CLKSTOP | SLCR_A9_CPU_RST) << cpu;
> > +	writel(reg, zynq_slcr_base + SLCR_A9_CPU_RST_CTRL_OFFSET);
> >  }
> >  
> 
> Hi!
> 
> Why do you also remove the comments? In my opinion they can stay.
I found the #defines descriptive enough

	Sören


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