linux-kernel - Re: [PATCH v2 2/3] iio: pressure: bmp280: Allow multiple chips id per family of devices

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Message-ID: <e3a73cfff0e91e22859ebdd671067ac06cfd9adf.camel@gmail.com>
Date:   Fri, 25 Aug 2023 11:30:28 +0200
From:   Angel Iglesias <ang.iglesiasg@...il.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>
Subject: Re: [PATCH v2 2/3] iio: pressure: bmp280: Allow multiple chips id
 per family of devices

On Wed, 2023-08-23 at 19:26 +0300, Andy Shevchenko wrote:
> On Wed, Aug 23, 2023 at 05:58:06PM +0200, Angel Iglesias wrote:
> > Improve device detection in certain chip families known to have various
> > chip ids.
> 
> IDs
> 
> ...
> 
> >  #include <linux/completion.h>
> >  #include <linux/pm_runtime.h>
> >  #include <linux/random.h>
> > +#include <linux/overflow.h>
> 
> Please, preserve ordering.
> 
> ...
> 
> >         struct bmp280_data *data;
> >         struct gpio_desc *gpiod;
> >         unsigned int chip_id;
> > -       int ret;
> > +       int ret, i;
> 
>         unsigned int i;
> 
> ...
> 
> > +       if (i == data->chip_info->num_chip_id) {
> > +               size_t nbuf;
> > +               char *buf;
> > +
> > +               // 0x<id>, so four chars per number plus one space + ENDL
> 
> > +               if (check_mul_overflow(5, data->chip_info->num_chip_id,
> > &nbuf))
> > +                       return ret;
> > +
> > +               buf = kmalloc_array(nbuf, sizeof(char), GFP_KERNEL);
> 
> We almost never do a array allocation for byte sizes. Instead of the above you
> need to use
> 
>                 buf = kmalloc_array(data->chip_info->num_chip_id, 5,
> GFP_KERNEL);
> 
> > +               if (!buf)
> 
> This check assumes that num_chip_id is never 0, so...
> 
> > +                       return ret;
> > +
> > +               for (i = 0; i < data->chip_info->num_chip_id; i++)
> > +                       snprintf(&buf[i*5], nbuf, "0x%x ", data->chip_info-
> > >chip_id[i]);
> 
> > +               buf[nbuf-1] = '\0';
> 
> ...this is redundant assignment. sprintf() guarantees the NUL termination.
> 
> > +
> > +               dev_err(dev, "bad chip id: expected [ %s ] got 0x%x\n", buf,
> > chip_id);
> 
> "...expected one of..."
> 
> > +               kfree(buf);
> > +               return ret;
> 
> Oh, I didn't get that you allocated memory only to print a message...

Yes, I just wanted to print the known IDs like before in a readable manner. If
it is overkill, I'll change it for a more generic error message.

> 
> >         }
> 
Kind regards,
Angel