Re: [PATCH v3 2/5] reset: Instantiate reset GPIO controller for shared reset-gpios

[Krzysztof Kozlowski]

On 15/01/2024 17:55, Philipp Zabel wrote:
> On Fr, 2024-01-12 at 17:36 +0100, Krzysztof Kozlowski wrote:
>>  
>> +static bool __reset_gpios_args_match(const struct of_phandle_args *a1,
>> +				     const struct of_phandle_args *a2)
>> +{
>> +	unsigned int i;
>> +
>> +	if (!a2)
>> +		return false;
>> +
>> +	if (a1->args_count != a2->args_count)
>> +		return false;
>> +
>> +	for (i = 0; i < a1->args_count; i++)
>> +		if (a1->args[i] != a2->args[i])
>> +			return false;
>> +
>> +	return true;
>> +}
> 
> How about making this
> 
> 	return a2 &&
> 	       a1->np == a2->np &&
> 	       a1->args_count == a2->args_count &&
> 	       !memcmp(a1->args, a2->args, sizeof(a1->args[0]) * a1->args_count);
> 
> ?
> 
> There's similar code in include/linux/cpufreq.h, maybe this could later
> be lifted into a common of_phandle_args_equal().

I'll make a helper because such long return is also not the fastest to
parse by brain.

> 
>> +
>> +static int __reset_add_reset_gpio_lookup(int id, struct device_node *np,
>> +					 unsigned int gpio,
>> +					 unsigned int of_flags)
>> +{
>> +	struct gpiod_lookup_table *lookup __free(kfree) = NULL;
>> +	struct gpio_device *gdev __free(gpio_device_put) = NULL;
>> +	char *label __free(kfree) = NULL;
>> +	unsigned int lookup_flags;
>> +
>> +	/*
>> +	 * Later we map GPIO flags between OF and Linux, however not all
>> +	 * constants from include/dt-bindings/gpio/gpio.h and
>> +	 * include/linux/gpio/machine.h match each other.
>> +	 */
>> +	if (of_flags > GPIO_ACTIVE_LOW) {
>> +		pr_err("reset-gpio code does not support GPIO flags %u for GPIO %u\n",
>> +			of_flags, gpio);
>> +		return -EINVAL;
>> +	}
>> +
>> +	gdev = gpio_device_find_by_fwnode(of_fwnode_handle(np));
>> +	if (!gdev)
>> +		return -EPROBE_DEFER;
>> +
>> +	label = kstrdup(gpio_device_get_label(gdev), GFP_KERNEL);
>> +	if (!label)
>> +		return -EINVAL;
> 
> The kstrdup() failure looks like it should be -ENOMEM to me.
> I'd check the gpio_device_get_label(gdev) return value separately.

OK, makes sense. One more local variable will be needed for that.

> 
> Is this going to be in v6.8-rc1, or does using gpio_device_get_label()
> introduce a dependency?

We were already in the merge window, so no problem here.
gpio_device_get_label() is in v6.8-rc1.


> 
>> +
>> +	/* Size: one lookup entry plus sentinel */
>> +	lookup = kzalloc(struct_size(lookup, table, 2), GFP_KERNEL);
>> +	if (!lookup)
>> +		return -ENOMEM;
>> +
>> +	lookup->dev_id = kasprintf(GFP_KERNEL, "reset-gpio.%d", id);
>> +	if (!lookup->dev_id)
>> +		return -ENOMEM;
>> +
>> +	lookup_flags = GPIO_PERSISTENT;
>> +	lookup_flags |= of_flags & GPIO_ACTIVE_LOW;
>> +	lookup->table[0] = GPIO_LOOKUP(no_free_ptr(label), gpio, "reset",
>> +				       lookup_flags);
>> +
>> +	gpiod_add_lookup_table(no_free_ptr(lookup));
>> +
>> +	return 0;
>> +}
>> +
>> +/*
>> + * @reset_args:	phandle to the GPIO provider with all the args like GPIO number
> 
> s/reset_//

ack

> 
>> + */
>> +static int __reset_add_reset_gpio_device(const struct of_phandle_args *args)
>> +{
>> +	struct reset_gpio_lookup *rgpio_dev;
>> +	struct platform_device *pdev;
>> +	int id, ret;
>> +
>> +	/*
>> +	 * Registering reset-gpio device might cause immediate
>> +	 * bind, resulting in its probe() registering new reset controller thus
>> +	 * taking reset_list_mutex lock via reset_controller_register().
>> +	 */
>> +	lockdep_assert_not_held(&reset_list_mutex);
>> +
>> +	mutex_lock(&reset_gpio_lookup_mutex);
>> +
>> +	list_for_each_entry(rgpio_dev, &reset_gpio_lookup_list, list) {
>> +		if (args->np == rgpio_dev->of_args.np) {
>> +			if (__reset_gpios_args_match(args, &rgpio_dev->of_args))
>> +				goto out; /* Already on the list, done */
>> +		}
>> +	}
>> +
>> +	id = ida_alloc(&reset_gpio_ida, GFP_KERNEL);
>> +	if (id < 0) {
>> +		ret = id;
>> +		goto err_unlock;
>> +	}
>> +
>> +	/*
>> +	 * Not freed in normal path, persisent subsystem data (which is assumed
>> +	 * also in the reset-gpio driver).
>> +	 */
>> +	rgpio_dev = kzalloc(sizeof(*rgpio_dev), GFP_KERNEL);
>> +	if (!rgpio_dev) {
>> +		ret = -ENOMEM;
>> +		goto err_ida_free;
>> +	}
>> +
>> +	ret = __reset_add_reset_gpio_lookup(id, args->np, args->args[0],
>> +					    args->args[1]);
>> +	if (ret < 0)
>> +		goto err_kfree;
>> +
>> +	rgpio_dev->of_args = *args;
>> +	/*
>> +	 * We keep the device_node reference, but of_args.np is put at the end
>> +	 * of __of_reset_control_get(), so get it one more time.
>> +	 * Hold reference as long as rgpio_dev memory is valid.
>> +	 */
>> +	of_node_get(rgpio_dev->of_args.np);
>> +	pdev = platform_device_register_data(NULL, "reset-gpio", id,
>> +					     &rgpio_dev->of_args,
>> +					     sizeof(rgpio_dev->of_args));
>> +	ret = PTR_ERR_OR_ZERO(pdev);
>> +	if (ret)
>> +		goto err_put;
>> +
>> +	list_add(&rgpio_dev->list, &reset_gpio_lookup_list);
>> +
>> +out:
>> +	mutex_unlock(&reset_gpio_lookup_mutex);
>> +
>> +	return 0;
>> +
>> +err_put:
>> +	of_node_put(rgpio_dev->of_args.np);
>> +err_kfree:
>> +	kfree(rgpio_dev);
>> +err_ida_free:
>> +	ida_free(&reset_gpio_ida, id);
>> +err_unlock:
>> +	mutex_unlock(&reset_gpio_lookup_mutex);
>> +
>> +	return ret;
>> +}
>> +
>> +static struct reset_controller_dev *__reset_find_rcdev(const struct of_phandle_args *args,
>> +						       bool gpio_fallback)
>> +{
>> +	struct reset_controller_dev *r, *rcdev;
> 
> Now that this is moved into a function, there's no need for the r,
> rcdev split anymore. Just return a match when found, and NULL at the
> end:
> 
> 	struct reset_controller_dev *rcdev;

Indeed, thanks.

> 
>> +
>> +	lockdep_assert_held(&reset_list_mutex);
>> +
>> +	rcdev = NULL;
>> +	list_for_each_entry(r, &reset_controller_list, list) {
> 
> 	list_for_each_entry(rcdev, &reset_controller_list, list) {
> 
>> +		if (args->np == r->of_node) {
>> +			if (gpio_fallback) {
>> +				if (__reset_gpios_args_match(args, r->of_args)) {
>> +					rcdev = r;
>> +					break;
> 
> 					return rcdev;
> 
>> +				}
>> +			} else {
>> +				rcdev = r;
>> +				break;
>> +			}
>> +		}
> 
> With the np check moved into __reset_gpios_args_match() above, the
> whole loop could be turned into:
> 
> 		if (gpio_fallback) {
> 			if (__reset_gpios_args_match(args, rcdev->of_args))
> 				return rcdev;
> 		} else {
> 			if (args->np == rcdev->of_node)
> 				return rcdev;
> 		}
> 
> Explicitly checking against rcdev->of_args->np instead of rcdev-
>> of_node in gpio_fallback mode could avoid false positives in case
> anybody ever creates a combined GPIO and reset controller device and
> then uses its GPIOs to drive a shared reset line..

ack

> 
>> +	}
>> +
>> +	return rcdev;
> 
> 	return NULL;

ack

> 
>> +}
>>
>>  struct reset_control *
>>  __of_reset_control_get(struct device_node *node, const char *id, int index,
>>  		       bool shared, bool optional, bool acquired)
>>  {
>> +	struct of_phandle_args args = {0};
> 
> Is this still needed?

I will double check.

> 
>> +	bool gpio_fallback = false;
>>  	struct reset_control *rstc;
>> -	struct reset_controller_dev *r, *rcdev;
>> -	struct of_phandle_args args;
>> +	struct reset_controller_dev *rcdev;
>>  	int rstc_id;
>>  	int ret;
>>  
>> @@ -839,39 +1028,49 @@ __of_reset_control_get(struct device_node *node, const char *id, int index,
>>  					 index, &args);
>>  	if (ret == -EINVAL)
>>  		return ERR_PTR(ret);
>> -	if (ret)
>> -		return optional ? NULL : ERR_PTR(ret);
>> +	if (ret) {
>> +		/*
>> +		 * There can be only one reset-gpio for regular devices, so
>> +		 * don't bother with GPIO index.
>> +		 */
>> +		ret = of_parse_phandle_with_args(node, "reset-gpios", "#gpio-cells",
>> +						 0, &args);
>> +		if (ret)
>> +			return optional ? NULL : ERR_PTR(ret);
>>  
>> -	mutex_lock(&reset_list_mutex);
>> -	rcdev = NULL;
>> -	list_for_each_entry(r, &reset_controller_list, list) {
>> -		if (args.np == r->of_node) {
>> -			rcdev = r;
>> -			break;
>> +		gpio_fallback = true;
>> +
>> +		ret = __reset_add_reset_gpio_device(&args);
>> +		if (ret) {
>> +			rstc = ERR_PTR(ret);
>> +			goto out_put;
>>  		}
>>  	}
>>  
>> +	mutex_lock(&reset_list_mutex);
>> +	rcdev = __reset_find_rcdev(&args, gpio_fallback);
>>  	if (!rcdev) {
>>  		rstc = ERR_PTR(-EPROBE_DEFER);
>> -		goto out;
>> +		goto out_unlock;
>>  	}
>>  
>>  	if (WARN_ON(args.args_count != rcdev->of_reset_n_cells)) {
> 
> Nice. I like that the __of_reset_control_get() changes are much less
> invasive now.
> 
>>  		rstc = ERR_PTR(-EINVAL);
>> -		goto out;
>> +		goto out_unlock;
>>  	}
>>  
>>  	rstc_id = rcdev->of_xlate(rcdev, &args);
>>  	if (rstc_id < 0) {
>>  		rstc = ERR_PTR(rstc_id);
>> -		goto out;
>> +		goto out_unlock;
>>  	}
>>  
>>  	/* reset_list_mutex also protects the rcdev's reset_control list */
>>  	rstc = __reset_control_get_internal(rcdev, rstc_id, shared, acquired);
>>  
>> -out:
>> +out_unlock:
>>  	mutex_unlock(&reset_list_mutex);
>> +out_put:
>>  	of_node_put(args.np);
>>  
>>  	return rstc;
>> diff --git a/include/linux/reset-controller.h b/include/linux/reset-controller.h
>> index 0fa4f60e1186..e064473215de 100644
>> --- a/include/linux/reset-controller.h
>> +++ b/include/linux/reset-controller.h
>> @@ -61,6 +61,9 @@ struct reset_control_lookup {
>>   * @dev: corresponding driver model device struct
>>   * @of_node: corresponding device tree node as phandle target
>>   * @of_reset_n_cells: number of cells in reset line specifiers
>> + * TODO: of_args have of_node, so we have here duplication
> 
> Any plans what to do about this? With the above changes we could
> mandate that either of_node or of_args should be set, never both.

Yes, makes sense. We could also drop of_node, but the code won't be more
readable.

Best regards,
Krzysztof