linux-kernel - Re: [PATCH v2] usb: core: downgrade log severity to info when descriptor unavailable

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Date:	Wed, 24 Sep 2014 17:56:52 +0000 (UTC)
From:	Scot Doyle <lkml14@...tdoyle.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
cc:	Alan Stern <stern@...land.harvard.edu>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Daniel Mack <daniel@...aq.de>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] usb: core: downgrade log severity to info when
 descriptor unavailable

On Tue, 23 Sep 2014, Greg Kroah-Hartman wrote:
> On Tue, Sep 23, 2014 at 07:12:40PM +0000, Scot Doyle wrote:
>> According to commit 0cce2eda19923e5e5ccc8b042dec5af87b3ffad0
>>     USB: fix LANGID=0 regression
>>
>> usb devices are not required to report string descriptors. Since they are
>> optional, log an info message instead of an error message.
>>
>> Signed-off-by: Scot Doyle <lkml14@...tdoyle.com>
>> ---
>>  drivers/usb/core/message.c | 8 ++++++--
>>  1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
>> index 0c8a7fc..da2f1f2 100644
>> --- a/drivers/usb/core/message.c
>> +++ b/drivers/usb/core/message.c
>> @@ -780,8 +780,12 @@ static int usb_get_langid(struct usb_device *dev, unsigned char *tbuf)
>>  	 * deal with strings at all. Set string_langid to -1 in order to
>>  	 * prevent any string to be retrieved from the device */
>>  	if (err < 0) {
>> -		dev_err(&dev->dev, "string descriptor 0 read error: %d\n",
>> -					err);
>> +		if (err == -EPIPE)
>> +			dev_info(&dev->dev,
>> +				 "string descriptor 0 read error: -EPIPE\n");
>> +		else
>> +			dev_err(&dev->dev,
>> +				"string descriptor 0 read error: %d\n", err);
>
> What real difference does this patch make?  What would a user do with
> -EPIPE?

Not much difference, except e.g. a log line that isn't red.

> And USB devices _are_ required to provide a string descriptor if they
> provide a string id, so your changelog body doesn't make much sense.  I
> suggest rewriting it to say they aren't required to provide a string
> descriptor for string "0".
>
> But even then, I don't understand the goal of this patch.

I'm happy to drop this patch request, since in my case the return value is 
-ENODATA, which is covered by the other patch: "[RFC PATCH] usb: core: log 
more general message on malformed LANGID descriptor"

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