RE: [PATCH v2 2/3] media: i2c: ov5645: Switch to assigned-clock-rates

[Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@bp.renesas.com>]

Hi Geert,

Thank you for the quick review.

> -----Original Message-----
> From: Geert Uytterhoeven <geert@linux-m68k.org>
> Sent: 12 March 2020 21:42
> To: Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@bp.renesas.com>
> Cc: Mauro Carvalho Chehab <mchehab@kernel.org>; Shawn Guo
> <shawnguo@kernel.org>; Sascha Hauer <s.hauer@pengutronix.de>;
> Pengutronix Kernel Team <kernel@pengutronix.de>; Rob Herring
> <robh+dt@kernel.org>; Mark Rutland <mark.rutland@arm.com>; Sakari
> Ailus <sakari.ailus@linux.intel.com>; NXP Linux Team <linux-imx@nxp.com>;
> Magnus Damm <magnus.damm@gmail.com>; Ezequiel Garcia
> <ezequiel@collabora.com>; open list:OPEN FIRMWARE AND FLATTENED
> DEVICE TREE BINDINGS <devicetree@vger.kernel.org>; Linux Kernel Mailing
> List <linux-kernel@vger.kernel.org>; Linux-Renesas <linux-renesas-
> soc@vger.kernel.org>; Fabio Estevam <festevam@gmail.com>; Linux ARM
> <linux-arm-kernel@lists.infradead.org>; Linux Media Mailing List <linux-
> media@vger.kernel.org>
> Subject: Re: [PATCH v2 2/3] media: i2c: ov5645: Switch to assigned-clock-
> rates
>
> Hi Prabhakar,
>
> On Thu, Mar 12, 2020 at 10:13 PM Lad Prabhakar <prabhakar.mahadev-
> lad.rj@bp.renesas.com> wrote:
> > This patch switches to assigned-clock-rates for specifying the clock rate.
> > The clk-conf.c internally handles setting the clock rate when
> > assigned-clock-rates is passed.
> >
> > The driver now sets the clock frequency only if the deprecated
> > property clock-frequency is defined instead assigned-clock-rates, this
> > is to avoid breakage with existing DT binaries.
> >
> > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-
> lad.rj@bp.renesas.com>
>
> Thanks for your patch!
>
> > --- a/drivers/media/i2c/ov5645.c
> > +++ b/drivers/media/i2c/ov5645.c
> > @@ -1055,6 +1055,7 @@ static int ov5645_probe(struct i2c_client *client)
> >         struct device_node *endpoint;
> >         struct ov5645 *ov5645;
> >         u8 chip_id_high, chip_id_low;
> > +       bool set_clk = false;
> >         unsigned int i;
> >         u32 xclk_freq;
> >         int ret;
> > @@ -1094,10 +1095,17 @@ static int ov5645_probe(struct i2c_client
> *client)
> >                 return PTR_ERR(ov5645->xclk);
> >         }
> >
> > -       ret = of_property_read_u32(dev->of_node, "clock-frequency",
> &xclk_freq);
> > +       ret = of_property_read_u32(dev->of_node, "assigned-clock-rates",
> > +                                  &xclk_freq);
> >         if (ret) {
>
> I think you can just leave out the above check...
>
> > -               dev_err(dev, "could not get xclk frequency\n");
> > -               return ret;
> > +               /* check if deprecated property clock-frequency is defined */
> > +               ret = of_property_read_u32(dev->of_node, "clock-frequency",
> > +                                          &xclk_freq);
> > +               if (ret) {
>
> ... and ignore the absence of the deprecated property.
>
> > +                       dev_err(dev, "could not get xclk frequency\n");
> > +                       return ret;
> > +               }
> > +               set_clk = true;
>
> I.e. just
>
>         /* check if deprecated property clock-frequency is defined */
>         xclk_freq = 0;
>         of_property_read_u32(dev->of_node, "clock-frequency", &xclk_freq);
>         if (xclk_freq) {
>                 ret = clk_set_rate(ov5645->xclk, xclk_freq);
>                 if (ret) {
>                         dev_err(dev, "could not set xclk frequency\n");
>                         return ret;
>                 }
>         } else {
>                 xclk_freq = clk_get_rate(ov5645->xclk, xclk_freq);
>         }
>
I did think about it initially, but realized the clk_get_rate may vary platform to platform
for example in G2E clk_get_rate() returns a frequency of 24242424 with
assigned-clock-rates set to  24000000 and probe would fail due to a check for
external clock must be 24MHz, with 1% tolerance.

Cheers,
--Prabhakar

> >         }
> >
> >         /* external clock must be 24MHz, allow 1% tolerance */ @@
> > -1107,10 +1115,12 @@ static int ov5645_probe(struct i2c_client *client)
> >                 return -EINVAL;
> >         }
> >
> > -       ret = clk_set_rate(ov5645->xclk, xclk_freq);
> > -       if (ret) {
> > -               dev_err(dev, "could not set xclk frequency\n");
> > -               return ret;
> > +       if (set_clk) {
> > +               ret = clk_set_rate(ov5645->xclk, xclk_freq);
> > +               if (ret) {
> > +                       dev_err(dev, "could not set xclk frequency\n");
> > +                       return ret;
> > +               }
>
> >         }
> >
> >         for (i = 0; i < OV5645_NUM_SUPPLIES; i++)
> > --
> > 2.7.4
> >
> >
> > _______________________________________________
> > linux-arm-kernel mailing list
> > linux-arm-kernel@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>
>
>
> --
> 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


Renesas Electronics Europe GmbH, Geschaeftsfuehrer/President: Carsten Jauch, Sitz der Gesellschaft/Registered office: Duesseldorf, Arcadiastrasse 10, 40472 Duesseldorf, Germany, Handelsregister/Commercial Register: Duesseldorf, HRB 3708 USt-IDNr./Tax identification no.: DE 119353406 WEEE-Reg.-Nr./WEEE reg. no.: DE 14978647