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

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Date:   Wed, 8 Jun 2022 14:03:32 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
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 02:49:14PM +0300, Andy Shevchenko wrote:
> 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.

Why not exactly?  match_true() above and device_match_any() have the
same signature from what I can tell:
	static int match_true(struct device *dev, void *data)
	int device_match_any(struct device *dev, const void *unused)

What am I missing, the const?

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

Yes, so let's fix it please, don't propagate bad patterns.

thanks,

greg k-h