linux-kernel - Re: [PATCH 04/11] staging: iio: adt7316: fix handling of dac high resolution option

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Message-ID: <20181214062618.GW3116@kadam>
Date:   Fri, 14 Dec 2018 09:26:18 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Jeremy Fertic <jeremyfertic@...il.com>
Cc:     devel@...verdev.osuosl.org, Lars-Peter Clausen <lars@...afoo.de>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        linux-iio@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Hartmut Knaack <knaack.h@....de>,
        Jonathan Cameron <jic23@...nel.org>
Subject: Re: [PATCH 04/11] staging: iio: adt7316: fix handling of dac high
 resolution option

On Thu, Dec 13, 2018 at 03:01:46PM -0700, Jeremy Fertic wrote:
> On Wed, Dec 12, 2018 at 11:23:16AM +0300, Dan Carpenter wrote:
> > On Tue, Dec 11, 2018 at 05:54:56PM -0700, Jeremy Fertic wrote:
> > > @@ -651,10 +649,12 @@ static ssize_t adt7316_store_da_high_resolution(struct device *dev,
> > >  	u8 config3;
> > >  	int ret;
> > >  
> > > +	if (chip->id == ID_ADT7318 || chip->id == ID_ADT7519)
> > > +		return -EPERM;
> > 
> > return -EINVAL is more appropriate than -EPERM.
> > 
> > regards,
> > dan carpenter
> > 
> 
> I chose -EPERM because the driver uses it quite a few times in similar
> circumstances.

Yeah.  I saw that when I reviewed the later patches in this series.

It's really not doing it right.  -EPERM means permission checks like
access_ok() failed so it's not appropriate.  -EINVAL is sort of general
purpose for invalid commands so it's probably the correct thing.

> At least with this driver, -EINVAL is used when the user
> attempts to write data that would never be valid. -EPERM is used when
> either the current device settings prevent some functionality from being
> used, or the device never supports that functionality. This patch is the
> latter, that these two chip ids never support this function.
> 
> I'll change to -EINVAL in a v2 series, but I wonder if I should hold off
> on a separate patch for other instances in this driver since it will be
> undergoing a substantial refactoring.

Generally, you should prefer kernel standards over driver standards and
especially for staging.  But it doesn't matter.  When I reviewed this
patch, I hadn't seen that the driver was doing it like this but now I
know so it's fine.  We can clean it all at once later if you want.

regards,
dan carpenter