Re: [PATCH v3 5/5] i2c: muxes: pca954x: Allow sharing reset GPIO

[Philipp Zabel <p.zabel@xxxxxxxxxxxxxx>]

On Di, 2024-01-16 at 19:58 +0000, Chris Packham wrote:
> On 17/01/24 04:18, Philipp Zabel wrote:
> > On Fr, 2024-01-12 at 17:36 +0100, Krzysztof Kozlowski wrote:
> > > From: Chris Packham <chris.packham@xxxxxxxxxxxxxxxxxxx>
> > > 
> > > Some hardware designs with multiple PCA954x devices use a reset GPIO
> > > connected to all the muxes. Support this configuration by making use of
> > > the reset controller framework which can deal with the shared reset
> > > GPIOs. Fall back to the old GPIO descriptor method if the reset
> > > controller framework is not enabled.
> > > 
> > > Signed-off-by: Chris Packham <chris.packham@xxxxxxxxxxxxxxxxxxx>
> > > Acked-by: Peter Rosin <peda@xxxxxxxxxx>
> > > Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
> > > Link: https://scanmail.trustwave.com/?c=20988&d=8p6m5Tfi2yYJWYV9xYGcYnz7UYxB6WTGTPkmGu7b8A&u=https%3a%2f%2flore%2ekernel%2eorg%2fr%2f20240108041913%2e7078-1-chris%2epackham%40alliedtelesis%2eco%2enz
> > > Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
> > > 
> > > ---
> > > 
> > > If previous patches are fine, then this commit is independent and could
> > > be taken via I2C.
> > > 
> > > Cc: Chris Packham <chris.packham@xxxxxxxxxxxxxxxxxxx>
> > > Cc: Bartosz Golaszewski <brgl@xxxxxxxx>
> > > Cc: Sean Anderson <sean.anderson@xxxxxxxx>
> > > ---
> > >   drivers/i2c/muxes/i2c-mux-pca954x.c | 46 ++++++++++++++++++++++++-----
> > >   1 file changed, 38 insertions(+), 8 deletions(-)
> > > 
> > > diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
> > > index 2219062104fb..1702e8d49b91 100644
> > > --- a/drivers/i2c/muxes/i2c-mux-pca954x.c
> > > +++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
> > > @@ -49,6 +49,7 @@
> > >   #include <linux/pm.h>
> > >   #include <linux/property.h>
> > >   #include <linux/regulator/consumer.h>
> > > +#include <linux/reset.h>
> > >   #include <linux/slab.h>
> > >   #include <linux/spinlock.h>
> > >   #include <dt-bindings/mux/mux.h>
> > > @@ -102,6 +103,9 @@ struct pca954x {
> > >   	unsigned int irq_mask;
> > >   	raw_spinlock_t lock;
> > >   	struct regulator *supply;
> > > +
> > > +	struct gpio_desc *reset_gpio;
> > > +	struct reset_control *reset_cont;
> > >   };
> > >   
> > >   /* Provide specs for the MAX735x, PCA954x and PCA984x types we know about */
> > > @@ -477,6 +481,35 @@ static int pca954x_init(struct i2c_client *client, struct pca954x *data)
> > >   	return ret;
> > >   }
> > >   
> > > +static int pca954x_get_reset(struct device *dev, struct pca954x *data)
> > > +{
> > > +	data->reset_cont = devm_reset_control_get_optional_shared(dev, NULL);
> > > +	if (IS_ERR(data->reset_cont))
> > > +		return dev_err_probe(dev, PTR_ERR(data->reset_cont),
> > > +				     "Failed to get reset\n");
> > > +	else if (data->reset_cont)
> > > +		return 0;
> > > +
> > > +	/*
> > > +	 * fallback to legacy reset-gpios
> > > +	 */
> > devm_reset_control_get_optional_shared() won't return NULL if the
> > "reset-gpios" property is found in the device tree, so the GPIO
> > fallback is dead code.
> 
> Hmm, I was attempting to handle the case where CONFIG_RESET_GPIO wasn't 
> set [...]
> [...] it looks like we'd get -EPROBE_DEFER. I could change to check
> for that or just remove the GPIO fallback entirely. Any preference?

I hadn't considered this.

If CONFIG_RESET_GPIO=n, devm_reset_control_get_optional_shared()
probably shouldn't return -EPROBE_DEFER. If we change that, the GPIO
fallback here can stay as is.

The alternative would be to drop the fallback and select RESET_GPIO.
Using -EPROBE_DEFER for fallback detection is no good, as there could
be a valid probe deferral if reset-gpio is compiled as a module that
will be loaded later.

regards
Philipp