linux-kernel - Re: [PATCH] serial: sprd: Return -EPROBE

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Message-ID: <CAB9BWhdKd93kJxPJv10X5uZ00O8d5NugoehX3_QtjmXQOMhDig@mail.gmail.com>
Date: Thu, 23 Oct 2025 10:10:46 +0800
From: wenhua lin <wenhua.lin1994@...il.com>
To: Chunyan Zhang <zhang.lyra@...il.com>
Cc: Wenhua Lin <Wenhua.Lin@...soc.com>, 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, 
	Xiongpeng Wu <xiongpeng.wu@...soc.com>, Zhaochen Su <Zhaochen.Su@...soc.com>, 
	Zhirong Qiu <Zhirong.Qiu@...soc.com>
Subject: Re: [PATCH] serial: sprd: Return -EPROBE_DEFER when uart clock is not ready

On Wed, Oct 22, 2025 at 2:55 PM Chunyan Zhang <zhang.lyra@...il.com> wrote:
>
> On Wed, 22 Oct 2025 at 11:09, Wenhua Lin <Wenhua.Lin@...soc.com> wrote:
> >
> > In sprd_clk_init(), when devm_clk_get() returns -EPROBE_DEFER
> > for either uart or source clock, we should propagate the
> > error instead of just warning and continuing with NULL clocks.
> >
> > Currently the driver only emits a warning when clock acquisition
> > fails and proceeds with NULL clock pointers. This can lead to
> > issues later when the clocks are actually needed. More importantly,
> > when the clock provider is not ready yet and returns -EPROBE_DEFER,
> > we should return this error to allow deferred probing.
> >
> > This change adds explicit checks for -EPROBE_DEFER after both:
> > 1. devm_clk_get(uport->dev, uart)
> > 2. devm_clk_get(uport->dev, source)
> >
> > When -EPROBE_DEFER is encountered, the function now returns
> > -EPROBE_DEFER to let the driver framework retry probing
> > later when the clock dependencies are resolved.
> >
> > Signed-off-by: Wenhua Lin <Wenhua.Lin@...soc.com>
> > ---
> >  drivers/tty/serial/sprd_serial.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/drivers/tty/serial/sprd_serial.c b/drivers/tty/serial/sprd_serial.c
> > index 8c9366321f8e..092755f35683 100644
> > --- a/drivers/tty/serial/sprd_serial.c
> > +++ b/drivers/tty/serial/sprd_serial.c
> > @@ -1133,6 +1133,9 @@ static int sprd_clk_init(struct uart_port *uport)
> >
> >         clk_uart = devm_clk_get(uport->dev, "uart");
> >         if (IS_ERR(clk_uart)) {
> > +               if (PTR_ERR(clk_uart) == -EPROBE_DEFER)
> > +                       return -EPROBE_DEFER;
> > +
>
> You are making this clock mandatory, sprd_serial driver could work as
> serial ports for logs output without this "uart" clock.

Hi chunyan:
   Thank you very much for your review.
   This clock is actually mandatory now，some SPRD project use default 26M clock,
   some new SPRD project use default 24M clock.  If driver can't parse
this clock correctly,
   driver will configure wrong baudrate and make the log garbled.

Thanks

>
> >                 dev_warn(uport->dev, "uart%d can't get uart clock\n",
> >                          uport->line);
> >                 clk_uart = NULL;
> > @@ -1140,6 +1143,9 @@ static int sprd_clk_init(struct uart_port *uport)
> >
> >         clk_parent = devm_clk_get(uport->dev, "source");
> >         if (IS_ERR(clk_parent)) {
> > +               if (PTR_ERR(clk_parent) == -EPROBE_DEFER)
> > +                       return -EPROBE_DEFER;
> > +
> >                 dev_warn(uport->dev, "uart%d can't get source clock\n",
> >                          uport->line);
> >                 clk_parent = NULL;
> > --
> > 2.34.1
> >