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

[Chris Packham <Chris.Packham@xxxxxxxxxxxxxxxxxxx>]

On 18/01/24 00:16, Philipp Zabel wrote:
> 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=_ban5W3xRzKSimJ9ijTJ74p10otfq8ZONfjVnBr6Fw&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.
I did consider adding `select RESET_GPIO` (or maybe just `imply 
RESET_GPIO`) initially but decided on the fallback as a way of avoiding 
surprises for existing users. I'll see if anyone else has a different 
suggestion but assuming nothing else changes I'll work with Krzystof to 
get an updated patch for this series.