Re: [PATCH 18/25] serial: sh-sci: Prepare for multiple clocks and baud rate generators

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Laurent,

On Fri, Nov 20, 2015 at 3:47 PM, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
> On Friday 20 November 2015 08:52:19 Geert Uytterhoeven wrote:
>> On Thu, Nov 19, 2015 at 10:04 PM, Laurent Pinchart wrote:
>> > On Thursday 19 November 2015 19:38:57 Geert Uytterhoeven wrote:
>> >> Refactor the clock and baud rate parameter code to ease adding support
>> >> for multiple clocks and baud rate generators later.
>> >> sci_scbrr_calc() now returns the bit rate error, so it can be compared
>> >> to the bit rate error for other baud rate generators.
>> >>
>> >> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
>> >> ---
>> >>
>> >>  drivers/tty/serial/sh-sci.c | 176 +++++++++++++++++++++++++-------------
>> >>  1 file changed, 120 insertions(+), 56 deletions(-)
>> >>
>> >> diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
>> >> index 726c96d5a511c222..12800e52f41953dc 100644
>> >> --- a/drivers/tty/serial/sh-sci.c
>> >> +++ b/drivers/tty/serial/sh-sci.c
>> >> @@ -2252,33 +2301,48 @@ static struct uart_ops sci_uart_ops = {
>> >>  static int sci_init_clocks(struct sci_port *sci_port, struct device
>> >>  *dev)
>> >>  {
>> >> -     /* Get the SCI functional clock. It's called "fck" on ARM. */
>> >> -     sci_port->fclk = devm_clk_get(dev, "fck");
>> >> -     if (PTR_ERR(sci_port->fclk) = -EPROBE_DEFER)
>> >> -             return -EPROBE_DEFER;
>> >> -     if (!IS_ERR(sci_port->fclk))
>> >> -             return 0;
>> >> +     const char *clk_names[] = {
>> >> +             [SCI_FCK] = "fck",
>> >> +     };
>> >> +     struct clk *clk;
>> >> +     unsigned int i;
>> >>
>> >> -     /*
>> >> -      * But it used to be called "sci_ick", and we need to maintain DT
>> >> -      * backward compatibility.
>> >> -      */
>> >> -     sci_port->fclk = devm_clk_get(dev, "sci_ick");
>> >> -     if (PTR_ERR(sci_port->fclk) = -EPROBE_DEFER)
>> >> -             return -EPROBE_DEFER;
>> >> -     if (!IS_ERR(sci_port->fclk))
>> >> -             return 0;
>> >> +     for (i = 0; i < SCI_NUM_CLKS; i++) {
>> >> +             clk = devm_clk_get(dev, clk_names[i]);
>> >> +             if (PTR_ERR(clk) = -EPROBE_DEFER)
>> >> +                     return -EPROBE_DEFER;
>> >>
>> >> -     /*
>> >> -      * Not all SH platforms declare a clock lookup entry for SCI
>> >> devices,
>> >> -      * in which case we need to get the global "peripheral_clk" clock.
>> >> -      */
>> >> -     sci_port->fclk = devm_clk_get(dev, "peripheral_clk");
>> >> -     if (!IS_ERR(sci_port->fclk))
>> >> -             return 0;
>> >> +             if (IS_ERR(clk) && i = SCI_FCK) {
>> >> +                     /*
>> >> +                      * "fck" used to be called "sci_ick", and we need
>> >> to
>> >> +                      * maintain DT backward compatibility.
>> >> +                      */
>> >> +                     clk = devm_clk_get(dev, "sci_ick");
>> >> +                     if (PTR_ERR(clk) = -EPROBE_DEFER)
>> >> +                             return -EPROBE_DEFER;
>> >> +
>> >> +                     if (!IS_ERR(clk))
>> >> +                             goto found;
>> >> +
>> >> +                     /*
>> >> +                      * Not all SH platforms declare a clock lookup
>> >> entry
>> >> +                      * for SCI devices, in which case we need to get
>> >> the
>> >> +                      * global "peripheral_clk" clock.
>> >> +                      */
>> >> +                     clk = devm_clk_get(dev, "peripheral_clk");
>> >> +                     if (!IS_ERR(clk))
>> >> +                             goto found;
>> >> +
>> >> +                     dev_err(dev, "failed to get functional clock\n");
>> >> +                     return PTR_ERR(clk);
>> >> +             }
>> >>
>> >> -     dev_err(dev, "failed to get functional clock\n");
>> >> -     return PTR_ERR(sci_port->fclk);
>> >> +found:
>> >> +             if (!IS_ERR(clk))
>> >> +                     dev_dbg(dev, "clk %u is %pC rate %pCr\n", i, clk,
>> >> clk);
>> >> +             sci_port->clks[i] = IS_ERR(clk) ? NULL : clk;
>> >
>> > Isn't it an issue that we can't tell apart the case where there is no
>> > clock specified in DT and the case where we can't get the clock due to
>> > another error ?
>>
>> All failures here are for optional clocks.
>> If the real failure is that the clock wasn't specified (or misspelled) in
>> DT, it should have been detected during the integration phase.
>
> There could be cases where the clock is correctly specified in DT but can't be
> retrieved due to a runtime error. I suppose that's mostly theoretical in our
> case though. Maybe a dev_dbg for the error case could be useful too ? Can we
> tell the case where the clock is not specified in DT apart from other errors
> (-EPROBE_DEFER aside as that case is already handled) ?

If the clock is not in clock/clock-names in DT, the error is definitely -ENOENT.

If the clock is specified in DT, it has a phandle to a clock node. If that
clock hasn't been instantiated yet, the error is EPROBE_DEFER.
Which means there are no other possible error values, right?

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