linux-kernel - Re: [PATCH 2/3] mfd: rohm-bd71828: Use software nodes for gpio-keys

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Message-ID: <jnf7z5hlljmoxw6ud3vuz4jaohh2ewjnpparh2dpbhef7ea7vp@up74k2viwhad>
Date: Mon, 18 Aug 2025 10:11:09 -0700
From: Dmitry Torokhov <dmitry.torokhov@...il.com>
To: Matti Vaittinen <mazziesaccount@...il.com>
Cc: Lee Jones <lee@...nel.org>, 
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Arnd Bergmann <arnd@...nel.org>, 
	Bartosz Golaszewski <brgl@...ev.pl>, Linus Walleij <linus.walleij@...aro.org>, 
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] mfd: rohm-bd71828: Use software nodes for gpio-keys

On Mon, Aug 18, 2025 at 09:56:07AM +0300, Matti Vaittinen wrote:
> On 18/08/2025 09:54, Matti Vaittinen wrote:
> > On 18/08/2025 01:47, Dmitry Torokhov wrote:
> > > Refactor the rohm-bd71828 MFD driver to use software nodes for
> > > instantiating the gpio-keys child device, replacing the old
> > > platform_data mechanism.
> > 
> > Thanks for doing this Dmitry! I believe I didn't understand how
> > providing the IRQs via swnode works... :)
> > 
> > If I visit the ROHM office this week, then I will try to test this using
> > the PMIC HW. (Next week I'll be in ELCE, and after it I have probably
> > already forgotten this...)
> > 
> > > The power key's properties are now defined using software nodes and
> > > property entries. The IRQ is passed as a resource attached to the
> > > platform device.
> > > 
> > > This will allow dropping support for using platform data for configuring
> > > gpio-keys in the future.
> > > 
> > > Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
> > > ---
> > >   drivers/mfd/rohm-bd71828.c | 81 +++++++++++++++++++++++++++-----------
> > >   1 file changed, 58 insertions(+), 23 deletions(-)
> > > 
> > > diff --git a/drivers/mfd/rohm-bd71828.c b/drivers/mfd/rohm-bd71828.c
> > > index a14b7aa69c3c..c29dde9996b7 100644
> > > --- a/drivers/mfd/rohm-bd71828.c
> > > +++ b/drivers/mfd/rohm-bd71828.c
> > > @@ -4,7 +4,6 @@
> > 
> > // ...snip
> > 
> > > +static int bd71828_reg_cnt;
> > > +
> > > +static int bd71828_i2c_register_swnodes(void)
> > > +{
> > > +    int error;
> > > +
> > > +    if (bd71828_reg_cnt == 0) {
> > 
> > Isn't this check racy...
> > 
> > > +        error = software_node_register_node_group(bd71828_swnodes);
> > > +        if (error)
> > > +            return error;
> > > +    }
> > > +
> > > +    bd71828_reg_cnt++;
> > 
> > ... with this...
> > 
> > > +    return 0;
> > > +}
> > > +
> > > +static void bd71828_i2c_unregister_swnodes(void *dummy)
> > > +{
> > > +    if (bd71828_reg_cnt != 0) {
> > 
> > ...this...
> > 
> > > +        software_node_unregister_node_group(bd71828_swnodes);
> > > +        bd71828_reg_cnt--;
> > 
> > ...and this? Perhaps add a mutex or use atomics?
> > 
> > Also, shouldn't the software_node_unregister_node_group() be only called
> > for the last instance to exit (Eg, "if (bd71828_reg_cnt == 0)" instead
> > of the "if (bd71828_reg_cnt != 0) {")?
> 
> Oh. Probably "if (bd71828_reg_cnt == 1)".

You are right, I am not sure what I was thinking when I wrote this.

I actually doubt that sharing of nodes between devices would work well.
But I believe these devices are singletons, it should not be possible to
have several of them in a single system, right? So maybe the best way is
to simply instantiate them in probe and bail out if they are already
registered.

Thanks.

-- 
Dmitry