linux-kernel - Re: [PATCH] mfd: omap-usb-tll: handle clk_prepare return code in usbtll_omap

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Message-ID: <20241110002954.1134398a@akair>
Date: Sun, 10 Nov 2024 00:29:54 +0100
From: Andreas Kemnade <andreas@...nade.info>
To: Karol P <karprzy7@...il.com>
Cc: aaro.koskinen@....fi, khilman@...libre.com, rogerq@...nel.org,
 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: handle clk_prepare return code in
 usbtll_omap_probe

Am Thu, 7 Nov 2024 12:12:52 +0100
schrieb Karol P <karprzy7@...il.com>:

> On Thu, 7 Nov 2024 at 00:15, Andreas Kemnade <andreas@...nade.info> wrote:
> >
> > Am Wed,  6 Nov 2024 23:33:24 +0100
> > schrieb Karol Przybylski <karprzy7@...il.com>:
> >  
> > > 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 return 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 | 8 ++++++--
> > >  1 file changed, 6 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/mfd/omap-usb-tll.c b/drivers/mfd/omap-usb-tll.c
> > > index 0f7fdb99c809..28446b082c85 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");
> > >
> > > @@ -251,7 +251,11 @@ static int usbtll_omap_probe(struct platform_device *pdev)
> > >               if (IS_ERR(tll->ch_clk[i]))
> > >                       dev_dbg(dev, "can't get clock : %s\n", clkname);  
> >
> > if you add more intensive error checking, then why is this error
> > ignored and not returned?  
> 
> Thank you for the feedback. It does seem that elevated error checking
> is not the way
> to go in this case. 

As far as I can see everything checks ch_clk[i] for validity before
usage. Also clk_enable() called later is checked which would catch
clk_prepare() failures, if there were even possible here.

So the only question which I am not 100% sure about is whether having
ch_clk sparsly populated is normal operation. If that is the case, then
more error checking is not useful. If not, then it might let us better
sleep. As said as far as I can see errors are catched later.

@Roger: what is your opintion towards this?

BTW: If you do this kind of work, you could also use W=1 or
CONFIG_WERROR during compiling to catch easy things. At least I see new
compile warnings with your patch. 

Regards,
Andreas