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

Boris BREZILLON
2014-09-08T19:22:26Z

On Mon, 8 Sep 2014 19:33:38 +0200
Alexandre Belloni <alexandre.belloni@free-electrons.com> wrote:

> 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).

Unfortunately, we can't get rid of this macro without modifying the
clk_lookup table in several arch/arm/mach-at91/<soc-name>.c files in
order to handle non DT/CCF cases (which will remain until all non DT
boards are moved to DT).
But I agree that this should be removed as soon as possible (AFAIR, all
SoCs have already been moved to the CCF).
How about adding a TODO comment ?

>
> > + 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
> >
>

--
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering