linux-kernel - Re: [PATCH 01/10] leds: pca953x: Use of_device_get_match

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Date:   Tue, 15 Oct 2019 15:41:58 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Wolfram Sang <wsa@...-dreams.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Riku Voipio <riku.voipio@....fi>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Pavel Machek <pavel@....cz>, Dan Murphy <dmurphy@...com>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>
Subject: Re: [PATCH 01/10] leds: pca953x: Use of_device_get_match_data()

Quoting Andy Shevchenko (2019-10-15 02:02:01)
> On Mon, Oct 14, 2019 at 11:54 PM Stephen Boyd <swboyd@...omium.org> wrote:
> > Quoting Andy Shevchenko (2019-10-14 10:50:06)
> > > On Sat, Oct 5, 2019 at 12:47 AM Stephen Boyd <swboyd@...omium.org> wrote:
> > > >
> > > > This driver can use the of_device_get_match_data() API to simplify the
> > > > code. Replace calls to of_match_device() with this newer API under the
> > > > assumption that where it is called will be when we know the device is
> > > > backed by a DT node. This nicely avoids referencing the match table when
> > > > it is undefined with configurations where CONFIG_OF=n.
> > >
> > > > +       devid = (int)(uintptr_t)of_device_get_match_data(dev);
> > >
> > > > +               devid = (int)(uintptr_t)of_device_get_match_data(&client->dev);
> > >
> > > This still leaves it OF-centric.
> > > Better to use device_get_match_data().
> > >
> > > Also, I'm thinking that following may help to clean a lot of the i2c
> > > client drivers
> > >
> > > static inline // perhaps no
> > > const void *i2c_device_get_match_data(struct i2c_client *client, const
> > > struct i2c_device_id *id)
> > > {
> > >   if (id)
> > >     return (const void *)id->driver_data;
> > >   return device_get_match_data(&client->dev);
> > > }
> > >
> >
> > Looks alright to me. Maybe device_get_match_data() can look at the bus
> > and call some bus op if the firmware match isn't present? Then we can
> > replace a bunch of these calls with device_get_match_data() and it will
> > "do the right thing" regardless of what bus or firmware the device is
> > running on.
> 
> It will be something ugly like
> 
> buses {
> #ifdef I2C
> &i2c_bus_type,
> #endif
> ...
> }
> 
> in the code. I won't do this.
> 
> See generic_match_buses[] for example.

Why is it like generic_match_buses[]? I thought it would look at
struct device::of_node or struct device::fw_node and try to extract
device data out that and if that fails it would fallback to some new
function like struct bus_type::get_match_data() that does the right
thing for the bus. In the case of i2c it would extract the i2c_client's
i2c_device_id pointer and return it onwards.