RE: [PATCH 2/3] spi: dw: Add basic runtime PM support

[Gareth Williams <gareth.williams.jx@xxxxxxxxxxx>]

Hi Geert,

> On Mon, Sep 17, 2019 at 07:36 PM Geert Uytterhoeven
> <geert@xxxxxxxxxxxxxx> wrote:
> 
> Hi Gareth,
> 
> On Mon, Sep 16, 2019 at 6:14 PM Gareth Williams
> <gareth.williams.jx@xxxxxxxxxxx> wrote:
> > > On Mon, Sep 16, 2019 at 15:36 PM Geert Uytterhoeven
> > > <geert@xxxxxxxxxxxxxx> wrote:
> > > On Fri, Sep 13, 2019 at 2:13 PM Gareth Williams
> > > <gareth.williams.jx@xxxxxxxxxxx> wrote:
> > > > From: Phil Edworthy <phil.edworthy@xxxxxxxxxxx>
> > > >
> > > > Enable runtime PM so that the clock used to access the registers
> > > > in the peripheral is turned on using a clock domain.
> > > >
> > > > Signed-off-by: Phil Edworthy <phil.edworthy@xxxxxxxxxxx>
> > > > Signed-off-by: Gareth Williams <gareth.williams.jx@xxxxxxxxxxx>
> > >
> > > Thanks for your patch!
> > >
> > > > --- a/drivers/spi/spi-dw.c
> > > > +++ b/drivers/spi/spi-dw.c
> > > > @@ -10,6 +10,7 @@
> > > >  #include <linux/module.h>
> > > >  #include <linux/highmem.h>
> > > >  #include <linux/delay.h>
> > > > +#include <linux/pm_runtime.h>
> > > >  #include <linux/slab.h>
> > > >  #include <linux/spi/spi.h>
> > > >
> > > > @@ -497,6 +498,9 @@ int dw_spi_add_host(struct device *dev, struct
> > > dw_spi *dws)
> > > >         if (dws->set_cs)
> > > >                 master->set_cs = dws->set_cs;
> > > >
> > > > +       pm_runtime_enable(dev);
> > > > +       pm_runtime_get_sync(dev);
> > >
> > > The second line keeps the device powered all the time.
> > > What about setting spi_controller.auto_runtime_pm = true, so the SPI
> > > code can manage its Runtime PM status?
> >
> > That makes sense and works on target, I will change this for V2.
> 
> > > I assume this will be called from drivers/spi/spi-dw-mmio.c, which
> > > already enables the clock explicitly all the timer?
> > Yes, spi-dw-mmio.c already enables the bus clock, however we want to
> > use clock
> >
> > domain to enable the clock and not explicitly provide pclk in the dts.
> > If there are no other uses of that pclk, we can remove that later on.
> 
> IC, that's useful sideband information.
> 
> "pclk" is indeed an optional clock.
> "ssi_clk" must be first.
> 
> However, to make use of the clock domain code, you still have to list "pclk"
> in DT, but use a different name, to avoid spi-dw-mmio.c enabling it all the
> time? Or do you plan to modify spi-dw-mmio.c for that?
> In the former case, you should document that in your bindings, which
> currently build on top of snps,dw-apb-ssi.txt, thus include "pclk".
We are intending to do the former, so I will include a binding update in V2 that
notes to rename "pclk" in the case a clock domain is in use. Thanks for pointing
this out.

> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-
> m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds

Kind Regards,

Gareth