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 13:31:58 +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,
thanks for the review.

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.

Francesco