linux-kernel - Re: [PATCH 3/3] HID: cp2112: fix broken gpio_direction

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Date:   Mon, 6 Nov 2017 14:58:46 +0100
From:   Sébastien Szymanski 
        <sebastien.szymanski@...adeus.com>
To:     Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc:     linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jiri Kosina <jikos@...nel.org>,
        Julien Boibessot <julien.boibessot@...adeus.com>
Subject: Re: [PATCH 3/3] HID: cp2112: fix broken gpio_direction_input callback

On 11/06/2017 09:11 AM, Benjamin Tissoires wrote:
> On Nov 02 2017 or thereabouts, Sébastien Szymanski wrote:
>> When everything goes smoothly, ret is set to 0 which makes the function
>> to return EIO error.
>>
>> Fixes: 8e9faa15469e ("HID: cp2112: fix gpio-callback error handling")
>> Signed-off-by: Sébastien Szymanski <sebastien.szymanski@...adeus.com>
>> ---
>>  drivers/hid/hid-cp2112.c | 5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/hid/hid-cp2112.c b/drivers/hid/hid-cp2112.c
>> index 28e3c18..f7754a6 100644
>> --- a/drivers/hid/hid-cp2112.c
>> +++ b/drivers/hid/hid-cp2112.c
>> @@ -205,12 +205,13 @@ static int cp2112_gpio_direction_input(struct gpio_chip *chip, unsigned offset)
>>  	ret = hid_hw_raw_request(hdev, CP2112_GPIO_CONFIG, buf,
>>  				 CP2112_GPIO_CONFIG_LENGTH, HID_FEATURE_REPORT,
>>  				 HID_REQ_SET_REPORT);
>> -	if (ret < 0) {
>> +	if (ret != CP2112_GPIO_CONFIG_LENGTH) {
> 
> Ack for this.

As explained in the interface specification, the device doesn't answer
to set reports, so the transfer should be CP2112_GPIO_CONFIG_LENGTH (5)
bytes.

> 
>>  		hid_err(hdev, "error setting GPIO config: %d\n", ret);
>>  		goto exit;
>>  	}
>>  
>> -	ret = 0;
>> +	mutex_unlock(&dev->lock);
>> +	return 0;
> 
> Wouldn't it be better to just turn
> - return ret < 0 ? ret : -EIO;
> into
> + return ret <= 0 ? ret : -EIO;
> at the end of the function?

Well, the commit I mentioned in the Fixes tag, changes from

- return ret <= 0 ? ret : -EIO;

to

+ return ret < 0 ? ret : -EIO;

because ret being 0 could mean that one of the hid_hw_raw_request
returned 0.

Regards,

> 
> I'd rather keep the same exit path in both cases, error or success.
> 
> Cheers,
> Benjamin
> 
> 
>>  
>>  exit:
>>  	mutex_unlock(&dev->lock);
>> -- 
>> 2.7.3
>>


-- 
Sébastien Szymanski
Software engineer, Armadeus Systems
Tel: +33 (0)9 72 29 41 44
Fax: +33 (0)9 72 28 79 26