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

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Date:   Mon, 6 Nov 2017 18:43:10 +0100
From:   Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:     Sébastien Szymanski 
        <sebastien.szymanski@...adeus.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 Nov 06 2017 or thereabouts, Sébastien Szymanski wrote:
> 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.

True.

So, commit 8e9faa15469e basically makes all transfert return -EIO and
should be reverted, right?

IMO, your commit should be:
if (ret != CP2112_GPIO_CONFIG_LENGTH) {
	hid_err(hdev, "error setting GPIO config: %d\n", ret);
	if (ret >= 0)
		ret = -EIO;
	goto exit;
}

ret = 0;
exit:
mutex_unlock(&dev->lock);
return ret;

How does that sound?

Cheers,
Benjamin

> 
> 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