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

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Date:	Fri, 20 Nov 2015 16:47:19 +0200
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Geert Uytterhoeven <geert+renesas@...der.be>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Simon Horman <horms@...ge.net.au>,
	Magnus Damm <magnus.damm@...il.com>,
	Yoshinori Sato <ysato@...rs.sourceforge.jp>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	Linux-sh list <linux-sh@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 18/25] serial: sh-sci: Prepare for multiple clocks and baud rate generators

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@...der.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

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