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

Boris BREZILLON
2014-09-08T19:37:49Z

On Mon, 8 Sep 2014 21:22:18 +0200
Boris BREZILLON <boris.brezillon@free-electrons.com> wrote:

> 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).

After taking a closer look at what should be modified, I think it's
worth it: there's only 5 impacted files (at91sam9260.c, at91sam9261.c,
at91sam9263.c, at91sam9rl.c and at91sam9g45.c) and adding a clk_lookup
entry is pretty easy.

Moreover we'll end up with a clean driver and won't have to bother
about cleaning it up when dropping non DT boards support.

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