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

Laurent Pinchart
2015-11-20T14:47:15Z

Hi Geert,

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) ?

--
Regards,

Laurent Pinchart