linux-kernel - Re: [PATCH 1/2] iio: pressure: mpl3115: do not rely on structure field ordering

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Date:   Wed, 1 Feb 2017 10:31:12 +0100 (CET)
From:   Peter Meerwald-Stadler <pmeerw@...erw.net>
To:     Peter Rosin <peda@...ntia.se>
cc:     linux-kernel@...r.kernel.org, Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Alison Schofield <amsfield22@...il.com>,
        Gregor Boirie <gregor.boirie@...rot.com>,
        Sanchayan Maity <maitysanchayan@...il.com>,
        Ken Lin <ken.lin@...antech.com>, linux-iio@...r.kernel.org
Subject: Re: [PATCH 1/2] iio: pressure: mpl3115: do not rely on structure
 field ordering


> >> Fixes a regression triggered by a change in the layout of
> >> struct iio_chan_spec, but the real bug is in the driver which assumed
> >> a specific structure layout in the first place.

> > what do you mean by 'driver which assumed a specific structure'?
> 
> Look again, the two bits are not OR:ed together as implied by the
> indentation. There is a comma between them, which put the ..._SCALE
> bit in the next field. That next field was .info_mask_shared_by_type
> before the patch adding the available attribute that triggered the
> regression and .info_mask_separate_available after it.

wow, now that you say it :)

since I wrote these drivers I can assure you that this is just a typo, use
of the 'specific structure' is a coincident

maybe adding your explanation regarding not ORing to the patch description
would be a good idea

I was confused by the change from 
.info_mask_separate to .info_mask_shared_by_type
a fix could have just changed
-  		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
			BIT(IIO_CHAN_INFO_SCALE),
+  		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
			BIT(IIO_CHAN_INFO_SCALE),
as originally intended

> Cheers,
> peda
> 
> > thanks, p.
> > 
> >> diff --git a/drivers/iio/pressure/mpl3115.c b/drivers/iio/pressure/mpl3115.c
> >> index cc3f84139157..525644a7442d 100644
> >> --- a/drivers/iio/pressure/mpl3115.c
> >> +++ b/drivers/iio/pressure/mpl3115.c
> >> @@ -190,7 +190,7 @@ static const struct iio_chan_spec mpl3115_channels[] = {
> >>  	{
> >>  		.type = IIO_PRESSURE,
> >>  		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
> >> -			BIT(IIO_CHAN_INFO_SCALE),
> >> +		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),
> >>  		.scan_index = 0,
> >>  		.scan_type = {
> >>  			.sign = 'u',
> >> @@ -203,7 +203,7 @@ static const struct iio_chan_spec mpl3115_channels[] = {
> >>  	{
> >>  		.type = IIO_TEMP,
> >>  		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
> >> -			BIT(IIO_CHAN_INFO_SCALE),
> >> +		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),
> >>  		.scan_index = 1,
> >>  		.scan_type = {
> >>  			.sign = 's',
> >>
> > 
> 

-- 

Peter Meerwald-Stadler
+43-664-2444418 (mobile)