Re: [PATCH] mfd: omap-usb-tll: check clk_prepare return code

[Andreas Kemnade <andreas@kemnade.info>]

Am Tue, 19 Nov 2024 16:16:42 +0200
schrieb Roger Quadros <rogerq@kernel.org>:

> On 19/11/2024 15:56, Andreas Kemnade wrote:
> > Am Tue, 19 Nov 2024 15:10:23 +0200
> > schrieb Roger Quadros <rogerq@kernel.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@gmail.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. 

Regards,
Andreas