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 [off-list ref] wrote:

quoted

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

quoted

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':

quoted

quoted

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	

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