linux-kernel - Re: [PATCH v4 2/2] media: i2c: add ov2735 image sensor driver

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Message-ID:
 <PN3P287MB35199EB9309448F3EDD43402FF51A@PN3P287MB3519.INDP287.PROD.OUTLOOK.COM>
Date: Thu, 17 Jul 2025 13:11:53 +0000
From: Hardevsinh Palaniya <hardevsinh.palaniya@...iconsignals.io>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
CC: "sakari.ailus@...ux.intel.com" <sakari.ailus@...ux.intel.com>,
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Subject: Re: [PATCH v4 2/2] media: i2c: add ov2735 image sensor driver

Hi Andy,

> On Thu, Jul 17, 2025 at 07:26:49AM +0000, Hardevsinh Palaniya wrote:
> > > On Wed, Jul 16, 2025 at 07:14:17PM +0530, Hardevsinh Palaniya wrote:
> 
> ...
> 
> > > > +static int ov2735_page_access(struct ov2735 *ov2735,
> > > > +                           u32 reg, void *val, int *err, bool is_read)
> > > > +{
> > > > +     u8 page = (reg >> CCI_REG_PRIVATE_SHIFT) & 0xff;
> > > > +     u32 addr = reg & ~CCI_REG_PRIVATE_MASK;
> > > > +     int ret = 0;
> > > > +
> > > > +     if (err && *err)
> > > > +             return *err;
> > > > +
> > > > +     mutex_lock(&ov2735->page_lock);
> > > > +
> > > > +     /* Perform page access before read/write */
> > > > +     if (ov2735->current_page != page) {
> > > > +             ret = cci_write(ov2735->cci, OV2735_REG_PAGE_SELECT, page, &ret);
> > > > +             if (ret)
> > > > +                     goto err_mutex_unlock;
> > > > +             ov2735->current_page = page;
> > > > +     }
> > > > +
> > > > +     if (is_read)
> > > > +             ret = cci_read(ov2735->cci, addr, (u64 *)val, err);
> > > > +     else
> > > > +             ret = cci_write(ov2735->cci, addr, *(u64 *)val, err);
> > > > +
> > > > +err_mutex_unlock:
> > >
> > > > +     if (ret && err)
> > >
> > > Why do you need to check for ret != 0?
> >
> > To prevents overwriting *err with 0 on successful operations, which could
> > obscure previous errors.
> 
> Can you elaborate a bit how the *err is not 0 at this point
> (assuming err != NULL)?

A previous operation have already failed and stored a non-
zero error code in *err.

Assuming this function is used in a sequence of write (or read) 
operations. If the current operation succeeds (i.e., ret == 0) and we 
unconditionally write *err = ret, we would overwrite the 
existing error with 0, falsely indicating that all operations 
were successful.

Therefore, the condition if (ret && err) ensures that we only 
update *err when there's a new error, preserving any previously 
recorded failures.

Let me know if you have a different suggestion for how this should 
be handled.

Best Regards,
Hardev