Re: [PATCH] gpio: devres: Handle nonexclusive GPIOs

[Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>]

Hi Linus,

On 2018-12-04 13:43, Linus Walleij wrote:
> When we get a nonexeclusive GPIO descriptor using managed
> resources, we should only add it to the list of managed
> resources once: on the first user. Augment the
> devm_gpiod_get_index() and devm_gpiod_get_from_of_node()
> calls to account for this by checking if the descriptor
> is already resource managed before we proceed to allocate
> a new resource management struct.
>
> Cc: Mark Brown <broonie@xxxxxxxxxx>
> Cc: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
> Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> Fixes: b0ce7b29bfcd ("regulator/gpio: Allow nonexclusive GPIO access")
> Reported-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> ---
> This fix is in response to an issue Marek saw in the fixups
> for resource-managed GPIO descriptors used with ena_gpiod
> in the regulator subsystem. I will merge this as a fix so
> the other fixes can assume it is in place once I have
> a confirmation is solves the problem.

gpiod_get_from_of_node() still needs a fix for non-exclusive access
(current linux-next lacks code for it), but I assume it will be handled
by separate patch.

The only problem I predict is the lack of refcounting. Assuming that you
would like to continue 'Regulator ena_gpiod fixups' approach, the first
call to devm_gpiod_unhinge() will remove 'all allocated instances', so
if the same descriptor will be used for more than one regulator, it must
be somehow handled...


> ---
>  drivers/gpio/gpiolib-devres.c | 50 ++++++++++++++++++++++++++---------
>  1 file changed, 38 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib-devres.c b/drivers/gpio/gpiolib-devres.c
> index e35751bf0ea8..304ad54dabb7 100644
> --- a/drivers/gpio/gpiolib-devres.c
> +++ b/drivers/gpio/gpiolib-devres.c
> @@ -98,15 +98,28 @@ struct gpio_desc *__must_check devm_gpiod_get_index(struct device *dev,
>  	struct gpio_desc **dr;
>  	struct gpio_desc *desc;
>  
> +	desc = gpiod_get_index(dev, con_id, idx, flags);
> +	if (IS_ERR(desc))
> +		return desc;
> +
> +	/*
> +	 * For non-exclusive GPIO descriptors, check if this descriptor is
> +	 * already under resource management by this device.
> +	 */
> +	if (flags & GPIOD_FLAGS_BIT_NONEXCLUSIVE) {
> +		struct devres *dres;
> +
> +		dres = devres_find(dev, devm_gpiod_release,
> +				   devm_gpiod_match, desc);
> +		if (dres)
> +			return desc;
> +	}
> +
>  	dr = devres_alloc(devm_gpiod_release, sizeof(struct gpio_desc *),
>  			  GFP_KERNEL);
> -	if (!dr)
> +	if (!dr) {
> +		gpiod_put(desc);
>  		return ERR_PTR(-ENOMEM);
> -
> -	desc = gpiod_get_index(dev, con_id, idx, flags);
> -	if (IS_ERR(desc)) {
> -		devres_free(dr);
> -		return desc;
>  	}
>  
>  	*dr = desc;
> @@ -140,15 +153,28 @@ struct gpio_desc *devm_gpiod_get_from_of_node(struct device *dev,
>  	struct gpio_desc **dr;
>  	struct gpio_desc *desc;
>  
> +	desc = gpiod_get_from_of_node(node, propname, index, dflags, label);
> +	if (IS_ERR(desc))
> +		return desc;
> +
> +	/*
> +	 * For non-exclusive GPIO descriptors, check if this descriptor is
> +	 * already under resource management by this device.
> +	 */
> +	if (dflags & GPIOD_FLAGS_BIT_NONEXCLUSIVE) {
> +		struct devres *dres;
> +
> +		dres = devres_find(dev, devm_gpiod_release,
> +				   devm_gpiod_match, desc);
> +		if (dres)
> +			return desc;
> +	}
> +
>  	dr = devres_alloc(devm_gpiod_release, sizeof(struct gpio_desc *),
>  			  GFP_KERNEL);
> -	if (!dr)
> +	if (!dr) {
> +		gpiod_put(desc);
>  		return ERR_PTR(-ENOMEM);
> -
> -	desc = gpiod_get_from_of_node(node, propname, index, dflags, label);
> -	if (IS_ERR(desc)) {
> -		devres_free(dr);
> -		return desc;
>  	}
>  
>  	*dr = desc;

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland