Re: [PATCH/RFC v9 01/19] leds: Add LED Flash class extension to the LED subsystem

[Jacek Anaszewski]

Hi Sakari,

On 12/09/2014 01:36 PM, Sakari Ailus wrote:
> Hi Jacek,
>
> On Thu, Dec 04, 2014 at 10:29:10AM +0100, Jacek Anaszewski wrote:
> ...
> > > > +static struct attribute *led_flash_strobe_attrs[] = {
> > > > +	&dev_attr_flash_strobe.attr,
> > > > +	NULL,
> > > > +};
> > > > +
> > > > +static struct attribute *led_flash_timeout_attrs[] = {
> > > > +	&dev_attr_flash_timeout.attr,
> > > > +	&dev_attr_max_flash_timeout.attr,
> > > > +	NULL,
> > > > +};
> > > > +
> > > > +static struct attribute *led_flash_brightness_attrs[] = {
> > > > +	&dev_attr_flash_brightness.attr,
> > > > +	&dev_attr_max_flash_brightness.attr,
> > > > +	NULL,
> > > > +};
> > > > +
> > > > +static struct attribute *led_flash_fault_attrs[] = {
> > > > +	&dev_attr_flash_fault.attr,
> > > > +	NULL,
> > > > +};
> > > > +
> > > > +static struct attribute *led_flash_sync_strobe_attrs[] = {
> > > > +	&dev_attr_flash_sync_strobe.attr,
> > > > +	NULL,
> > > > +};
> > > > +
> > > > +static const struct attribute_group led_flash_strobe_group = {
> > > > +	.attrs = led_flash_strobe_attrs,
> > > > +};
> > > > +
> > > > +static const struct attribute_group led_flash_timeout_group = {
> > > > +	.attrs = led_flash_timeout_attrs,
> > > > +};
> > > > +
> > > > +static const struct attribute_group led_flash_brightness_group = {
> > > > +	.attrs = led_flash_brightness_attrs,
> > > > +};
> > > > +
> > > > +static const struct attribute_group led_flash_fault_group = {
> > > > +	.attrs = led_flash_fault_attrs,
> > > > +};
> > > > +
> > > > +static const struct attribute_group led_flash_sync_strobe_group = {
> > > > +	.attrs = led_flash_sync_strobe_attrs,
> > > > +};
> > > > +
> > > > +static const struct attribute_group *flash_groups[] = {
> > > > +	&led_flash_strobe_group,
> > > > +	NULL,
> > > > +	NULL,
> > > > +	NULL,
> > > > +	NULL,
> > > > +	NULL,
> > > > +	NULL
> > > > +};
> > > > +
> > > > +static void led_flash_resume(struct led_classdev *led_cdev)
> > > > +{
> > > > +	struct led_classdev_flash *flash = lcdev_to_flash(led_cdev);
> > > > +
> > > > +	call_flash_op(flash, flash_brightness_set, flash->brightness.val);
> > > > +	call_flash_op(flash, timeout_set, flash->timeout.val);
> > > > +}
> > > > +
> > > > +static void led_flash_init_sysfs_groups(struct led_classdev_flash *flash)
> > > > +{
> > > > +	struct led_classdev *led_cdev = &flash->led_cdev;
> > > > +	const struct led_flash_ops *ops = flash->ops;
> > > > +	int num_sysfs_groups = 1;
> > > > +
> > > > +	if (ops->flash_brightness_set)
> > > > +		flash_groups[num_sysfs_groups++] = &led_flash_brightness_group;
> > > > +
> > > > +	if (ops->timeout_set)
> > > > +		flash_groups[num_sysfs_groups++] = &led_flash_timeout_group;
> > > > +
> > > > +	if (ops->fault_get)
> > > > +		flash_groups[num_sysfs_groups++] = &led_flash_fault_group;
> > > > +
> > > > +	if (led_cdev->flags & LED_DEV_CAP_COMPOUND)
> > > > +		flash_groups[num_sysfs_groups++] = &led_flash_sync_strobe_group;
> > > > +
> > > > +	led_cdev->groups = flash_groups;
> > >
> > > Shouldn't you have groups local to the device instead? If you register
> > > another flash device bad things will happen if the ops the device supports
> > > are different.
> >
> > The groups are local to the device. A LED class device is registered
> > with device_create_with_groups called from led_classdev_register
> > function. It is passed led_cdev->groups in the fifth argument.
>
> The groups pointer will be stored in struct device. If you have another
> driver using different groups, it will affect the groups for all flash
> devices that use the same groups pointer. I'm not sure what exactly would
> follow from that but I'd rather not change them once the device is created.

I had to take another look at this to understand the problem.
I think that the best option will be making flash_groups array
a member of struct led_classdev_flash.

> > > > +}
> > > > +
> > > > +int led_classdev_flash_register(struct device *parent,
> > > > +				struct led_classdev_flash *flash)
> > > > +{
> > > > +	struct led_classdev *led_cdev;
> > > > +	const struct led_flash_ops *ops;
> > > > +	int ret;
> > > > +
> > > > +	if (!flash)
> > >
> > > Do you have a use case for this?
> >
> > This is just a guard against NULL pointer dereference. Maybe it is
> > indeed redundant, as the driver developer can easily check its
> > origin during implementation.
>
> Fine for me.

Fine regarding my explanation or you agree that it is redundant?

Best Regards,
Jacek Anaszewski

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