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

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Message-ID: <20130718072106.GB15514@pengutronix.de>
Date:	Thu, 18 Jul 2013 09:21:06 +0200
From:	Steffen Trumtrar <s.trumtrar@...gutronix.de>
To:	Soren Brinkmann <soren.brinkmann@...inx.com>
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 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.

Regards,
Steffen

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