linux-kernel - Re: [PATCH v1 2/2] spi: Use device_find_first

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Date:   Wed, 8 Jun 2022 14:49:14 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Mark Brown <broonie@...nel.org>, linux-kernel@...r.kernel.org,
        linux-spi@...r.kernel.org, "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH v1 2/2] spi: Use device_find_first_child() instead of
 custom approach

On Wed, Jun 08, 2022 at 01:36:17PM +0200, Greg Kroah-Hartman wrote:
> On Tue, Jun 07, 2022 at 11:20:58PM +0300, Andy Shevchenko wrote:
> > We have already a helper to get the first child device, use it and
> > drop custom approach.
> > 
> > Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > ---
> >  drivers/spi/spi.c | 9 ++-------
> >  1 file changed, 2 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
> > index ea09d1b42bf6..87dc8773108b 100644
> > --- a/drivers/spi/spi.c
> > +++ b/drivers/spi/spi.c
> > @@ -2613,11 +2613,6 @@ int spi_slave_abort(struct spi_device *spi)
> >  }
> >  EXPORT_SYMBOL_GPL(spi_slave_abort);
> >  
> > -static int match_true(struct device *dev, void *data)
> > -{
> > -	return 1;
> > -}
> > -
> >  static ssize_t slave_show(struct device *dev, struct device_attribute *attr,
> >  			  char *buf)
> >  {
> > @@ -2625,7 +2620,7 @@ static ssize_t slave_show(struct device *dev, struct device_attribute *attr,
> >  						   dev);
> >  	struct device *child;
> >  
> > -	child = device_find_child(&ctlr->dev, NULL, match_true);
> > +	child = device_find_first_child(&ctlr->dev);
> >  	return sprintf(buf, "%s\n",
> >  		       child ? to_spi_device(child)->modalias : NULL);
> >  }
> 
> Horrible naming convention asside, what is this really showing?  I do
> not see this documented in Documentation/ABI/ anywhere, so can it just
> be dropped entirely?
> 
> Ah, it's in Documentation/spi/spi-summary.rst not where it belongs...
> 
> Looks like "any" of the child devices could match here, so it's just
> finding the first one by default.  So you aren't explicitly asking for
> the real first device, you could return the last one as well, and it
> would still work as there is just "one" device in this list from what I
> can tell.
> 
> So is does this really deserve a new driver core api call?

As I said I noticed more places like this (*) and the problem is that I can't
simply use device_match_any() because of the different prototype.

I agree that all thing should be using _any instead of _first.

*) e.g. ptp_ocp.

-- 
With Best Regards,
Andy Shevchenko