Re: [PATCH 4/5] rtc: at91sam9: retain slow clock and check its rate

Alexandre Belloni
2014-09-08T17:33:45Z

On 03/09/2014 at 10:45:33 +0200, Boris Brezillon wrote :
> The RTT block is using the slow clock and expect it to run at 32KHz.
> Now that we moved to the CCF it's better to retain the clk reference so
> that the CCF can't disable the slow clock considering it is unused.
>
> Signed-off-by: Boris BREZILLON <boris.brezillon@free-electrons.com>
> ---
> drivers/rtc/rtc-at91sam9.c | 24 ++++++++++++++++++++++++
> 1 file changed, 24 insertions(+)
>
> diff --git a/drivers/rtc/rtc-at91sam9.c b/drivers/rtc/rtc-at91sam9.c
> index 57014b7..5c5093b 100644
> --- a/drivers/rtc/rtc-at91sam9.c
> +++ b/drivers/rtc/rtc-at91sam9.c
> @@ -21,6 +21,7 @@
> #include <linux/slab.h>
> #include <linux/platform_data/atmel.h>
> #include <linux/io.h>
> +#include <linux/clk.h>
>
> /*
> * This driver uses two configurable hardware resources that live in the
> @@ -74,6 +75,7 @@ struct sam9_rtc {
> u32 imr;
> void __iomem *gpbr;
> int irq;
> + struct clk *sclk;
> };
>
> #define rtt_readl(rtc, field) \
> @@ -373,6 +375,25 @@ static int at91_rtc_probe(struct platform_device *pdev)
> return ret;
> }
>
> + /* Retain slow clk if it is specified in the DT.
> + * Do not complain if slow clk is missing, but check its rate
> + * if it is available.
> + */
> + rtc->sclk = devm_clk_get(&pdev->dev, NULL);
> + if (!IS_ERR(rtc->sclk)) {
> + if (clk_get_rate(rtc->sclk) != AT91_SLOW_CLOCK) {

I would not bother doing that check but use the value for MR instead of
AT91_SLOW_CLOCK (see my previous mail).

> + dev_err(&pdev->dev,
> + "Invalid slow clock rate (expecting %lu got %lu)",
> + (unsigned long)AT91_SLOW_CLOCK,
> + clk_get_rate(rtc->sclk));
> + return -EINVAL;
> + }
> +
> + ret = clk_prepare_enable(rtc->sclk);
> + if (ret)
> + return ret;
> + }
> +
> /* NOTE: sam9260 rev A silicon has a ROM bug which resets the
> * RTT on at least some reboots. If you have that chip, you must
> * initialize the time from some external source like a GPS, wall
> @@ -397,6 +418,9 @@ static int at91_rtc_remove(struct platform_device *pdev)
> /* disable all interrupts */
> rtt_writel(rtc, MR, mr & ~(AT91_RTT_ALMIEN | AT91_RTT_RTTINCIEN));
>
> + if (!IS_ERR(rtc->sclk))
> + clk_disable_unprepare(rtc->sclk);
> +
> return 0;
> }
>
> --
> 1.9.1
>

--
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering