linux-kernel - Re: [PATCH V2] serial: sprd: Use devm_clk_get

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Message-ID: <CAAfSe-vXq6Q6bzSbkWYaB656NqD64+9XdVkKdKVid6sZo3fu0Q@mail.gmail.com>
Date: Wed, 10 Dec 2025 15:12:17 +0800
From: Chunyan Zhang <zhang.lyra@...il.com>
To: Wenhua Lin <Wenhua.Lin@...soc.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Jiri Slaby <jirislaby@...nel.org>, 
	Orson Zhai <orsonzhai@...il.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>, 
	Cixi Geng <cixi.geng@...ux.dev>, linux-kernel@...r.kernel.org, 
	linux-serial@...r.kernel.org, wenhua lin <wenhua.lin1994@...il.com>, 
	Xiongpeng Wu <xiongpeng.wu@...soc.com>, Zhaochen Su <Zhaochen.Su@...soc.com>, 
	Zhirong Qiu <Zhirong.Qiu@...soc.com>
Subject: Re: [PATCH V2] serial: sprd: Use devm_clk_get_optional() to get the
 input clock

On Wed, 10 Dec 2025 at 14:36, Wenhua Lin <Wenhua.Lin@...soc.com> wrote:
>
> Simplify the code which fetches the input clock by using
> devm_clk_get_optional(). If no input clock is present
> devm_clk_get_optional() will return NULL instead of an error
> which matches the behavior of the old code.

This commit message is not describing the key point of its changes.

>
> Signed-off-by: Wenhua Lin <Wenhua.Lin@...soc.com>
> ---
> Change in V2:
> -Change title.
> -Change commit message.
> -Replace devm_clk_get() by devm_clk_get_optional() and drop NULL assignment.
> -Delete the sprd_uart_is_console function, after using the devm_clk_get_optional()
>  interface, this conditional check is redundant.
> ---
>  drivers/tty/serial/sprd_serial.c | 40 +++++++-------------------------
>  1 file changed, 9 insertions(+), 31 deletions(-)
>
> diff --git a/drivers/tty/serial/sprd_serial.c b/drivers/tty/serial/sprd_serial.c
> index 8c9366321f8e..83ce77b435ee 100644
> --- a/drivers/tty/serial/sprd_serial.c
> +++ b/drivers/tty/serial/sprd_serial.c
> @@ -1115,34 +1115,21 @@ static void sprd_remove(struct platform_device *dev)
>                 uart_unregister_driver(&sprd_uart_driver);
>  }
>
> -static bool sprd_uart_is_console(struct uart_port *uport)
> -{
> -       struct console *cons = sprd_uart_driver.cons;
> -
> -       if ((cons && cons->index >= 0 && cons->index == uport->line) ||
> -           of_console_check(uport->dev->of_node, SPRD_TTY_NAME, uport->line))
> -               return true;
> -
> -       return false;
> -}
> -
>  static int sprd_clk_init(struct uart_port *uport)
>  {
>         struct clk *clk_uart, *clk_parent;
>         struct sprd_uart_port *u = container_of(uport, struct sprd_uart_port, port);
>
> -       clk_uart = devm_clk_get(uport->dev, "uart");
> +       clk_uart = devm_clk_get_optional(uport->dev, "uart");
>         if (IS_ERR(clk_uart)) {
> -               dev_warn(uport->dev, "uart%d can't get uart clock\n",
> -                        uport->line);
> -               clk_uart = NULL;
> +               return dev_err_probe(uport->dev, PTR_ERR(clk_uart),
> +                       "uart%d can't get uart clock\n", uport->line);

No, as I said before, you cannot do like this, this patch is making
the clocks mandatory, sprd_serial driver could work as serial ports
for logs output without this "uart" clock.

It is very useful for early debugging when the clock driver is not even ready.

If other SPRD serials' default clock is 24M rather than 26M, like I
said in the last version patch, you can set default clock according to
the compatible string, that's saying make SPRD_DEFAULT_SOURCE_CLK to
be an element of "of_device_id.data".

So NAK for this change, sorry!

Thanks,
Chunyan

>         }
>
> -       clk_parent = devm_clk_get(uport->dev, "source");
> +       clk_parent = devm_clk_get_optional(uport->dev, "source");
>         if (IS_ERR(clk_parent)) {
> -               dev_warn(uport->dev, "uart%d can't get source clock\n",
> -                        uport->line);
> -               clk_parent = NULL;
> +               return dev_err_probe(uport->dev, PTR_ERR(clk_parent),
> +                       "uart%d can't get source clock\n", uport->line);
>         }
>
>         if (!clk_uart || clk_set_parent(clk_uart, clk_parent))
> @@ -1150,19 +1137,10 @@ static int sprd_clk_init(struct uart_port *uport)
>         else
>                 uport->uartclk = clk_get_rate(clk_uart);
>
> -       u->clk = devm_clk_get(uport->dev, "enable");
> +       u->clk = devm_clk_get_optional(uport->dev, "enable");
>         if (IS_ERR(u->clk)) {
> -               if (PTR_ERR(u->clk) == -EPROBE_DEFER)
> -                       return -EPROBE_DEFER;
> -
> -               dev_warn(uport->dev, "uart%d can't get enable clock\n",
> -                       uport->line);
> -
> -               /* To keep console alive even if the error occurred */
> -               if (!sprd_uart_is_console(uport))
> -                       return PTR_ERR(u->clk);
> -
> -               u->clk = NULL;
> +               return dev_err_probe(uport->dev, PTR_ERR(u->clk),
> +                       "uart%d can't get enable clock\n", uport->line);
>         }
>
>         return 0;
> --
> 2.34.1
>