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

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Message-ID: <5d6ccb9f-a8f1-45eb-b54a-cd66e637a2cc@kernel.org>
Date: Tue, 19 Nov 2024 16:16:42 +0200
From: Roger Quadros <rogerq@...nel.org>
To: Andreas Kemnade <andreas@...nade.info>
Cc: Karol Przybylski <karprzy7@...il.com>, 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 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.

> 
>>> -		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) 
> 
> Regards,
> Andreas

-- 
cheers,
-roger