linux-kernel - Re: [PATCH v1 2/2] usb: typec: mux: gpio-sbu: Make enable gpio optional

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Date: Fri, 24 May 2024 14:51:10 +0200
From: Francesco Dolcini <francesco@...cini.it>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Francesco Dolcini <francesco@...cini.it>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Francesco Dolcini <francesco.dolcini@...adex.com>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	Bjorn Andersson <andersson@...nel.org>
Subject: Re: [PATCH v1 2/2] usb: typec: mux: gpio-sbu: Make enable gpio
 optional

Hello Dmitry,

On Fri, May 24, 2024 at 02:42:04PM +0300, Dmitry Baryshkov wrote:
> On Fri, May 24, 2024 at 01:31:58PM +0200, Francesco Dolcini wrote:
> > On Fri, May 24, 2024 at 12:56:15PM +0300, Dmitry Baryshkov wrote:
> > > On Fri, May 24, 2024 at 09:10:34AM +0200, Francesco Dolcini wrote:
> > > > From: Francesco Dolcini <francesco.dolcini@...adex.com>
> > > > 
> > > > The enable gpio is not required when the SBU mux is used only for
> > > > orientation, make it optional.
> > > > 
> > > > Signed-off-by: Francesco Dolcini <francesco.dolcini@...adex.com>
> > > > ---
> > > >  drivers/usb/typec/mux/gpio-sbu-mux.c | 11 ++++++++---
> > > >  1 file changed, 8 insertions(+), 3 deletions(-)
> > > > 
> > > > diff --git a/drivers/usb/typec/mux/gpio-sbu-mux.c b/drivers/usb/typec/mux/gpio-sbu-mux.c
> > > > index 374168482d36..cf44259980a1 100644
> > > > --- a/drivers/usb/typec/mux/gpio-sbu-mux.c
> > > > +++ b/drivers/usb/typec/mux/gpio-sbu-mux.c
> > ...
> > > > @@ -66,6 +66,9 @@ static int gpio_sbu_mux_set(struct typec_mux_dev *mux,
> > > >  {
> > > >  	struct gpio_sbu_mux *sbu_mux = typec_mux_get_drvdata(mux);
> > > >  
> > > > +	if (!sbu_mux->enable_gpio)
> > > > +		return -EOPNOTSUPP;
> > > 
> > > Can we skip registering the mux if there is no enable_gpio? This can
> > > save users from the unexpected errors during runtime.
> > 
> > Yes, I considered this option.
> > 
> > The rationale for the current implementation is that if the device tree is
> > correct (no mode-switch property, when enable-gpios is not present), nobody
> > will call gpio_sbu_mux_set() so no runtime error is possible. If the
> > configuration in the DT is not correct you get this runtime error.
> > 
> > With your proposal in case the DT configuration is not correct there will be no
> > errors from the kernel, but the functionality will not work.
> 
> I'm slightly biased maybe, but I prefer an error from probe (or
> dependent devices being deferred). On the other hand, current motto is
> that 'the kernel should not duplicate dt-validate's work'.

I am in favor of "the kernel should not duplicate dt-validate's work".

Now the question is if you are ok with the current implementation or you want
me to change the way you suggested.

Or maybe there is a third variant, not doing the return -EOPNOTSUPP and
registering gpio_sbu_mux_set() even if the gpio get returns NULL. This is a
one-line patch and everything will work just fine.

Francesco