[U-Boot] [PATCH v6 02/12] serial: ns16550: Support clocks via phandle

[Simon Glass]

Hi Paul,

On 4 August 2016 at 04:29, Paul Burton <paul.burton at imgtec.com> wrote:
> Previously ns16550 compatible UARTs probed via device tree have needed
> their device tree nodes to contain a clock-frequency property. An
> alternative to this commonly used with Linux is to reference a clock via
> a phandle. This patch allows U-Boot to support that, retrieving the
> clock frequency by probing the appropriate clock device.
>
> For example, a system might choose to provide the UART base clock as a
> reference to a clock common to multiple devices:
>
>   sys_clk: clock {
>     compatible = "fixed-clock";
>     #clock-cells = <0>;
>     clock-frequency = <10000000>;
>   };
>
>   uart0: uart at 10000000 {
>     compatible = "ns16550a";
>     reg = <0x10000000 0x1000>;
>     clocks = <&sys_clk>;
>   };
>
>   uart1: uart at 10000000 {
>     compatible = "ns16550a";
>     reg = <0x10001000 0x1000>;
>     clocks = <&sys_clk>;
>   };
>
> This removes the need for the frequency information to be duplicated in
> multiple nodes and allows the device tree to be more descriptive of the
> system.
>
> Signed-off-by: Paul Burton <paul.burton at imgtec.com>
> Reviewed-by: Simon Glass <sjg at chromium.org>
>
> ---
>
> Changes in v6:
> - Ignore -ENOSYS from clk_get_by_index too, for systems with CONFIG_CLK=n
>
> Changes in v5: None
> Changes in v4: None
> Changes in v3: None
> Changes in v2:
> - Propogate non-ENODEV errors from clk_get_by_index
>
>  drivers/serial/ns16550.c | 19 ++++++++++++++++---
>  1 file changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/serial/ns16550.c b/drivers/serial/ns16550.c
> index 88fca15..af317cb 100644
> --- a/drivers/serial/ns16550.c
> +++ b/drivers/serial/ns16550.c
> @@ -5,6 +5,7 @@
>   */
>
>  #include <common.h>
> +#include <clk.h>
>  #include <dm.h>
>  #include <errno.h>
>  #include <fdtdec.h>
> @@ -352,6 +353,8 @@ int ns16550_serial_ofdata_to_platdata(struct udevice *dev)
>  {
>         struct ns16550_platdata *plat = dev->platdata;
>         fdt_addr_t addr;
> +       struct clk clk;
> +       int err;
>
>         /* try Processor Local Bus device first */
>         addr = dev_get_addr(dev);
> @@ -397,9 +400,19 @@ int ns16550_serial_ofdata_to_platdata(struct udevice *dev)
>                                      "reg-offset", 0);
>         plat->reg_shift = fdtdec_get_int(gd->fdt_blob, dev->of_offset,
>                                          "reg-shift", 0);
> -       plat->clock = fdtdec_get_int(gd->fdt_blob, dev->of_offset,
> -                                    "clock-frequency",
> -                                    CONFIG_SYS_NS16550_CLK);
> +
> +       err = clk_get_by_index(dev, 0, &clk);
> +       if (!err) {
> +               plat->clock = clk_get_rate(&clk);

While I think this is a good change, it breaks boards which have a
clock in the device tree but don't support it in their driver.

I think you can fix it by checking the error value from
clk_get_rate(), i.e. something like:

if (!err) {
     err = clk_get_rate(&clk);
     if (!IS_ERR_VALUE(err))
          plat->clock = err;
} else if ...

> +       } else if (err != -ENODEV && err != -ENOSYS) {
> +               debug("ns16550 failed to get clock\n");
> +               return err;
> +       }
> +
> +       if (!plat->clock)
> +               plat->clock = fdtdec_get_int(gd->fdt_blob, dev->of_offset,
> +                                            "clock-frequency",
> +                                            CONFIG_SYS_NS16550_CLK);
>         if (!plat->clock) {
>                 debug("ns16550 clock not defined\n");
>                 return -EINVAL;
> --
> 2.9.2
>

Regards,
Simon