linux-kernel - Re: [PATCH] mfd: omap-usb-tll: check clk

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Message-ID: <CAKwoAfrvqUxPat9a+4LjRKYx2LZ=n6Q2H+ir3KYkBBj+Rv_HWQ@mail.gmail.com>
Date: Thu, 5 Dec 2024 22:54:05 +0100
From: Karol P <karprzy7@...il.com>
To: Andreas Kemnade <andreas@...nade.info>
Cc: Roger Quadros <rogerq@...nel.org>, aaro.koskinen@....fi, khilman@...libre.com, 
	tony@...mide.com, lee@...nel.org, linux-omap@...r.kernel.org, 
	linux-kernel@...r.kernel.org, skhan@...uxfoundation.org
Subject: Re: [PATCH] mfd: omap-usb-tll: check clk_prepare return code

On Tue, 26 Nov 2024 at 23:06, Andreas Kemnade <andreas@...nade.info> wrote:
>
> Am Tue, 19 Nov 2024 16:16:42 +0200
> schrieb Roger Quadros <rogerq@...nel.org>:
>
> > On 19/11/2024 15:56, Andreas Kemnade wrote:
> > > Am Tue, 19 Nov 2024 15:10:23 +0200
> > > schrieb Roger Quadros <rogerq@...nel.org>:
> > >
> > >> Hi,
> > >>
> > >> On 13/11/2024 23:16, Karol Przybylski wrote:
> > >>> clk_prepare() is called in usbtll_omap_probe to fill clk array.
> > >>> Return code is not checked, leaving possible error condition unhandled.
> > >>>
> > >>> Added variable to hold return value from clk_prepare() and dev_dbg statement
> > >>> when it's not successful.
> > >>>
> > >>> Found in coverity scan, CID 1594680
> > >>>
> > >>> Signed-off-by: Karol Przybylski <karprzy7@...il.com>
> > >>> ---
> > >>>  drivers/mfd/omap-usb-tll.c | 11 +++++++----
> > >>>  1 file changed, 7 insertions(+), 4 deletions(-)
> > >>>
> > >>> diff --git a/drivers/mfd/omap-usb-tll.c b/drivers/mfd/omap-usb-tll.c
> > >>> index 0f7fdb99c809..2e9319ee1b74 100644
> > >>> --- a/drivers/mfd/omap-usb-tll.c
> > >>> +++ b/drivers/mfd/omap-usb-tll.c
> > >>> @@ -202,7 +202,7 @@ static int usbtll_omap_probe(struct platform_device *pdev)
> > >>>   struct device                           *dev =  &pdev->dev;
> > >>>   struct usbtll_omap                      *tll;
> > >>>   void __iomem                            *base;
> > >>> - int                                     i, nch, ver;
> > >>> + int                                     i, nch, ver, err;
> > >>>
> > >>>   dev_dbg(dev, "starting TI HSUSB TLL Controller\n");
> > >>>
> > >>> @@ -248,10 +248,13 @@ static int usbtll_omap_probe(struct platform_device *pdev)
> > >>>                                   "usb_tll_hs_usb_ch%d_clk", i);
> > >>>           tll->ch_clk[i] = clk_get(dev, clkname);
> > >>>
> > >>> -         if (IS_ERR(tll->ch_clk[i]))
> > >>> +         if (IS_ERR(tll->ch_clk[i])) {
> > >>>                   dev_dbg(dev, "can't get clock : %s\n", clkname);
> > >
> > > if you want dev_err() later, then why not here?
> >
> > Because clk is optional. If it is not there then we should not complain.
> > But if it is there then it needs to be enabled successfully.
> >
> I guess you mean *prepared*, the clock is enabled later (with error
> checking). But your reasoning makes sense.
>
> > >
> > >>> -         else
> > >>> -                 clk_prepare(tll->ch_clk[i]);
> > >>> +         } else {
> > >>> +                 err = clk_prepare(tll->ch_clk[i]);
> > >>> +                 if (err)
> > >>> +                         dev_dbg(dev, "clock prepare error for: %s\n", clkname);
> > >>
> > >> dev_err()?
> > >>
> > > So why do you want a different return handling here? (I doubt there is
> > > any clock having a real prepare() involved here)
> > >
> > > As said in an earlier incarnation of this patch, the real question is
> > > whether having partial clocks available is a valid operating scenario.
> > > If yes, then the error should be ignored. If no, then bailing out early
> > > is a good idea.
> >
> > In the DT binding, clocks is optional. So if it doesn't exist it is not
> > an error condition.
> >
> > >
> > > clk_prepare() errors are catched by failing clk_enable() later,
> > > ch_clk[i] is checked later, too.
> > >
> > >> I think we should return the error in this case.
> > >> (after unpreparing the prepared clocks and clk_put())
> > >>
> > > and pm_runtime_put_sync(dev)
>
> which can probably be done before dealing with the clocks. It is only
> needed for the register access.

I'm fairly new to this subsystem and I'm trying to understand the
conclusion. In the end, we should add dev_err() here after
clk_prepare() with appropriate handling?

>
> Regards,
> Andreas

Best regards,
Karol