Re: [PATCH 2/2] iio: adc: at91: fix wrong channel number in triggered buffer mode

From: Song Qiang
Date: Sat Sep 22 2018 - 07:20:26 EST


On Sat, Sep 22, 2018 at 11:36:16AM +0100, Jonathan Cameron wrote:
> On Fri, 21 Sep 2018 15:26:03 +0800
> kbuild test robot <lkp@xxxxxxxxx> wrote:
>
> > Hi Eugen,
> This one is leaving me stumped...
>
> Anyone care to point out what I'm missing that is wrong here?
>
> Also Eugen, please don't cc stable on a patch directly. It is fine to send
> a backport request once a patch has hit mainline, but before that it's just
> adding noise to a list as they won't take it directly anyway.
>
> Jonathan
>

Hi Jonathan,

I run some test code here and found out that C compilers don't allow
us to assign a 'const int *' to 'int *', while assign a 'const int' to
'int' is fine.
In this case this driver was tring to assign a 'struct iio_chan_spec
const *' to a 'struct iio_chan_spec *', mostly because of this issue.

I googled this issue and someone on stack overflow said it's because
this kind of action will break the check mechanism of 'const'.

yours,
Song Qiang

> >
> > I love your patch! Perhaps something to improve:
> >
> > [auto build test WARNING on iio/togreg]
> > [also build test WARNING on v4.19-rc4 next-20180919]
> > [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
> >
> > url: https://github.com/0day-ci/linux/commits/Eugen-Hristev/iio-adc-at91-fix-acking-DRDY-irq-on-simple-conversions/20180920-215908
> > base: https://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git togreg
> > config: arm-allmodconfig (attached as .config)
> > compiler: arm-linux-gnueabi-gcc (Debian 7.2.0-11) 7.2.0
> > reproduce:
> > wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> > chmod +x ~/bin/make.cross
> > # save the attached .config to linux build tree
> > GCC_VERSION=7.2.0 make.cross ARCH=arm
> >
> > All warnings (new ones prefixed by >>):
> >
> > drivers/iio/adc/at91_adc.c: In function 'at91_adc_trigger_handler':
> > >> drivers/iio/adc/at91_adc.c:257:8: warning: assignment discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
> > chan = idev->channels + i;
> > ^
> >
> > vim +/const +257 drivers/iio/adc/at91_adc.c
> >
> > 245
> > 246 static irqreturn_t at91_adc_trigger_handler(int irq, void *p)
> > 247 {
> > 248 struct iio_poll_func *pf = p;
> > 249 struct iio_dev *idev = pf->indio_dev;
> > 250 struct at91_adc_state *st = iio_priv(idev);
> > 251 struct iio_chan_spec *chan;
> > 252 int i, j = 0;
> > 253
> > 254 for (i = 0; i < idev->masklength; i++) {
> > 255 if (!test_bit(i, idev->active_scan_mask))
> > 256 continue;
> > > 257 chan = idev->channels + i;
> > 258 st->buffer[j] = at91_adc_readl(st, AT91_ADC_CHAN(st, chan->channel));
> > 259 j++;
> > 260 }
> > 261
> > 262 iio_push_to_buffers_with_timestamp(idev, st->buffer, pf->timestamp);
> > 263
> > 264 iio_trigger_notify_done(idev->trig);
> > 265
> > 266 /* Needed to ACK the DRDY interruption */
> > 267 at91_adc_readl(st, AT91_ADC_LCDR);
> > 268
> > 269 enable_irq(st->irq);
> > 270
> > 271 return IRQ_HANDLED;
> > 272 }
> > 273
> >
> > ---
> > 0-DAY kernel test infrastructure Open Source Technology Center
> > https://lists.01.org/pipermail/kbuild-all Intel Corporation
>