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

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Message-ID: <CAB9BWheCDwbS+=pwAK0+HyY+q5=DQ_2tUQXaFoH5-GKtVUDnBw@mail.gmail.com>
Date: Wed, 10 Dec 2025 14:48:40 +0800
From: wenhua lin <wenhua.lin1994@...il.com>
To: Andy Shevchenko <andriy.shevchenko@...el.com>
Cc: Wenhua Lin <Wenhua.Lin@...soc.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Jiri Slaby <jirislaby@...nel.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Orson Zhai <orsonzhai@...il.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>, 
	Chunyan Zhang <zhang.lyra@...il.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 Thu, Nov 27, 2025 at 5:05 PM Andy Shevchenko
<andriy.shevchenko@...el.com> wrote:
>
> On Thu, Nov 27, 2025 at 04:44:08PM +0800, wenhua lin wrote:
> > On Wed, Nov 26, 2025 at 8:57 PM Andy Shevchenko
> > <andriy.shevchenko@...el.com> wrote:
> > > On Wed, Oct 22, 2025 at 11:08:40AM +0800, Wenhua Lin wrote:
>
> ...
>
> > > >       clk_uart = devm_clk_get(uport->dev, "uart");
> > > >       if (IS_ERR(clk_uart)) {
> > > > +             if (PTR_ERR(clk_uart) == -EPROBE_DEFER)
> > > > +                     return -EPROBE_DEFER;
> > > > +
> > > >               dev_warn(uport->dev, "uart%d can't get uart clock\n",
> > > >                        uport->line);
> > > >               clk_uart = NULL;
> > >
> > > AFAICS this still ignores other issues, what should be done here is to
> > > replace devm_clk_get() by devm_clk_get_optional() and drop this NULL
> > > assignment.
>
> >    The main reason for this change is that the UART driver is
> > built-in, while the CLK driver is loaded as a module (ko).
> >    There may be a situation where the UART driver is loaded first. If
> > an EPROBE_DEFER error occurs, the driver will return directly
> >    and continue waiting for the CLK driver to complete loading.
> >    If this interface is changed to devm_clk_get_optional, in scenarios
> > where dependent components are not yet loaded,
> >    it will no longer return EPROBE_DEFER but instead return null. This
> > behavior may not align with the desired outcome.
>
> No, the _optional does exactly what your code does with the better approach
> that may return other errors _in addition to_ the current state of affairs.
>
> So, please switch to _optional variant and drop all that unneeded dances.
>
>         clk_uart = devm_clk_get_optional(uport->dev, "uart");
>         if (IS_ERR(clk_uart)) {
>                 return dev_err_probe(uport->dev, PTR_ERR(clk_uart),
>                                      "uart%d can't get uart clock\n", uport->line);
>
> this will return an error when clock is present, but can't be retrieved.
> When there is no clock provided at all, it will return NULL.
>
> > > >       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;
>
> Ditto.
>
> --
> With Best Regards,
> Andy Shevchenko
>
>

Hi Andy:
  Thank you for your valuable feedback.
  We have implemented the changes in patch V2 and submitted a revised version.

Thanks