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Date:   Thu, 12 Jul 2018 23:41:02 +0200
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Baolin Wang <baolin.wang@...aro.org>
Cc:     Pavel Machek <pavel@....cz>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/2] leds: core: Introduce generic pattern interface

Hi Baolin,

On 07/12/2018 02:24 PM, Baolin Wang wrote:
> Hi Jacek,
> 
> On 12 July 2018 at 05:10, Jacek Anaszewski <jacek.anaszewski@...il.com> wrote:
>> Hi Baolin.
>>
>>
>> On 07/11/2018 01:02 PM, Baolin Wang wrote:
>>>
>>> Hi Jacek and Pavel,
>>>
>>> On 29 June 2018 at 13:03, Baolin Wang <baolin.wang@...aro.org> wrote:
>>>>
>>>> From: Bjorn Andersson <bjorn.andersson@...aro.org>
>>>>
>>>> Some LED controllers have support for autonomously controlling
>>>> brightness over time, according to some preprogrammed pattern or
>>>> function.
>>>>
>>>> This adds a new optional operator that LED class drivers can implement
>>>> if they support such functionality as well as a new device attribute to
>>>> configure the pattern for a given LED.
>>>>
>>>> [Baolin Wang did some minor improvements.]
>>>>
>>>> Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
>>>> Signed-off-by: Baolin Wang <baolin.wang@...aro.org>
>>>> ---
>>>> Changes from v2:
>>>>    - Change kernel version to 4.19.
>>>>    - Force user to return error pointer if failed to issue pattern_get().
>>>>    - Use strstrip() to trim trailing newline.
>>>>    - Other optimization.
>>>>
>>>> Changes from v1:
>>>>    - Add some comments suggested by Pavel.
>>>>    - Change 'delta_t' can be 0.
>>>>
>>>> Note: I removed the pattern repeat check and will get the repeat number
>>>> by adding
>>>> one extra file named 'pattern_repeat' according to previous discussion.
>>>> ---
>>>
>>>
>>> Do you have any comments for this version patch set? Thanks.
>>
>>
>> I tried modifying uleds.c driver to support pattern ops, but
>> I'm getting segfault when doing "cat pattern". I didn't give
>> it serious testing and analysis - will do it at weekend.
>>
>> It also drew my attention to the issue of desired pattern sysfs
>> interface semantics on uninitialized pattern. In your implementation
>> user seems to be unable to determine if the pattern is activated
>> or not. We should define the semantics for this use case and
>> describe it in the documentation. Possibly pattern could
>> return alone new line character then.
> 
> I am not sure I get your points correctly. If user writes values to
> pattern interface which means we activated the pattern.
> If I am wrong, could you elaborate on the issue you concerned? Thanks.

Now I see, that writing empty string disables the pattern, right?
It should be explicitly stated in the pattern file documentation.

>> This is the code snippet I've used for testing pattern interface:
>>
>> static struct led_pattern ptrn[10];
>> static int ptrn_len;
>>
>> static int uled_pattern_clear(struct led_classdev *ldev)
>> {
>>          return 0;
>> }
>>
>> static int uled_pattern_set(struct led_classdev *ldev,
>>                                    struct led_pattern *pattern,
>>                                    int len)
>> {
>>          int i;
>>
>>          for (i = 0; i < len; i++) {
>>                  ptrn[i].brightness = pattern[i].brightness;
>>                  ptrn[i].delta_t = pattern[i].delta_t;
>>          }
>>
>>          ptrn_len = len;
>>
>>          return 0;
>> }
>>
>> static struct led_pattern *uled_pattern_get(struct led_classdev *ldev,
>>                                                    int *len)
>> {
>>          int i;
>>
>>          for (i = 0; i < ptrn_len; i++) {
>>                  ptrn[i].brightness = 3;
>>                  ptrn[i].delta_t = 5;
>>          }
>>
>>          *len = ptrn_len;
>>
>>          return ptrn;
>>
>> }
> 
> The reason you met segfault when doing "cat pattern" is you should not
> return one static pattern array, since in pattern_show() it will help
> to free the pattern memory, could you change to return one pattern
> pointer with dynamic allocation like my patch 2?

Thanks for pointing this out.

>>>>    Documentation/ABI/testing/sysfs-class-led |   17 +++++
>>>>    drivers/leds/led-class.c                  |  119
>>>> +++++++++++++++++++++++++++++
>>>>    include/linux/leds.h                      |   19 +++++
>>>>    3 files changed, 155 insertions(+)
>>>>
>>>> diff --git a/Documentation/ABI/testing/sysfs-class-led
>>>> b/Documentation/ABI/testing/sysfs-class-led
>>>> index 5f67f7a..e01ac55 100644
>>>> --- a/Documentation/ABI/testing/sysfs-class-led
>>>> +++ b/Documentation/ABI/testing/sysfs-class-led
>>>> @@ -61,3 +61,20 @@ Description:
>>>>                   gpio and backlight triggers. In case of the backlight
>>>> trigger,
>>>>                   it is useful when driving a LED which is intended to
>>>> indicate
>>>>                   a device in a standby like state.
>>>> +
>>>> +What: /sys/class/leds/<led>/pattern
>>>> +Date: June 2018
>>>> +KernelVersion: 4.19
>>>> +Description:
>>>> +       Specify a pattern for the LED, for LED hardware that support
>>>> +       altering the brightness as a function of time.
>>>> +
>>>> +       The pattern is given by a series of tuples, of brightness and
>>>> +       duration (ms). The LED is expected to traverse the series and
>>>> +       each brightness value for the specified duration. Duration of
>>>> +       0 means brightness should immediately change to new value.
>>>> +
>>>> +       As LED hardware might have different capabilities and precision
>>>> +       the requested pattern might be slighly adjusted by the driver
>>>> +       and the resulting pattern of such operation should be returned
>>>> +       when this file is read.
>>>> diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
>>>> index 3c7e348..8a685a2 100644
>>>> --- a/drivers/leds/led-class.c
>>>> +++ b/drivers/leds/led-class.c
>>>> @@ -74,6 +74,123 @@ static ssize_t max_brightness_show(struct device
>>>> *dev,
>>>>    }
>>>>    static DEVICE_ATTR_RO(max_brightness);
>>>>
>>>> +static ssize_t pattern_show(struct device *dev,
>>>> +                           struct device_attribute *attr, char *buf)
>>>> +{
>>>> +       struct led_classdev *led_cdev = dev_get_drvdata(dev);
>>>> +       struct led_pattern *pattern;
>>>> +       size_t offset = 0;
>>>> +       int count, n, i;
>>>> +
>>>> +       if (!led_cdev->pattern_get)
>>>> +               return -EOPNOTSUPP;
>>
>>
>> Please check this in led_classdev_register() and fail
>> if pattern_set is initialized, but pattern_get or pattern_clear not.
> 
> Sure.
> 
>>>> +       pattern = led_cdev->pattern_get(led_cdev, &count);
>>>> +       if (IS_ERR(pattern))
>>>> +               return PTR_ERR(pattern);
>>>> +
>>>> +       for (i = 0; i < count; i++) {
>>>> +               n = snprintf(buf + offset, PAGE_SIZE - offset, "%d %d ",
>>>> +                            pattern[i].brightness, pattern[i].delta_t);
>>>> +
>>>> +               if (offset + n >= PAGE_SIZE)
>>>> +                       goto err_nospc;
>>>> +
>>>> +               offset += n;
>>>> +       }
>>>> +
>>>> +       buf[offset - 1] = '\n';
>>>> +
>>>> +       kfree(pattern);
>>>> +       return offset;
>>>> +
>>>> +err_nospc:
>>>> +       kfree(pattern);
>>>> +       return -ENOSPC;
>>>> +}
>>>> +
>>>> +static ssize_t pattern_store(struct device *dev,
>>>> +                            struct device_attribute *attr,
>>>> +                            const char *buf, size_t size)
>>>> +{
>>>> +       struct led_classdev *led_cdev = dev_get_drvdata(dev);
>>>> +       struct led_pattern *pattern = NULL;
>>>> +       unsigned long val;
>>>> +       char *sbegin;
>>>> +       char *elem;
>>>> +       char *s;
>>>> +       int ret, len = 0;
>>>> +       bool odd = true;
>>>> +
>>>> +       sbegin = kstrndup(buf, size, GFP_KERNEL);
>>>> +       if (!sbegin)
>>>> +               return -ENOMEM;
>>>> +
>>>> +       /*
>>>> +        * Trim trailing newline, if the remaining string is empty,
>>>> +        * clear the pattern.
>>>> +        */
>>>> +       s = strstrip(sbegin);
>>>> +       if (!*s) {
>>>> +               ret = led_cdev->pattern_clear(led_cdev);
>>>> +               goto out;
>>>> +       }
>>>> +
>>>> +       pattern = kcalloc(size, sizeof(*pattern), GFP_KERNEL);
>>>> +       if (!pattern) {
>>>> +               ret = -ENOMEM;
>>>> +               goto out;
>>>> +       }
>>>> +
>>>> +       /* Parse out the brightness & delta_t touples */
>>>> +       while ((elem = strsep(&s, " ")) != NULL) {
>>>> +               ret = kstrtoul(elem, 10, &val);
>>>> +               if (ret)
>>>> +                       goto out;
>>>> +
>>>> +               if (odd) {
>>>> +                       pattern[len].brightness = val;
>>>> +               } else {
>>>> +                       pattern[len].delta_t = val;
>>>> +                       len++;
>>>> +               }
>>>> +
>>>> +               odd = !odd;
>>>> +       }
>>>> +
>>>> +       /*
>>>> +        * Fail if we didn't find any data points or last data point was
>>>> partial
>>>> +        */
>>>> +       if (!len || !odd) {
>>>> +               ret = -EINVAL;
>>>> +               goto out;
>>>> +       }
>>>> +
>>>> +       ret = led_cdev->pattern_set(led_cdev, pattern, len);
>>>> +
>>>> +out:
>>>> +       kfree(pattern);
>>>> +       kfree(sbegin);
>>>> +       return ret < 0 ? ret : size;
>>>> +}
>>>> +static DEVICE_ATTR_RW(pattern);
>>>> +
>>>> +static umode_t led_class_attrs_mode(struct kobject *kobj,
>>>> +                                   struct attribute *attr, int index)
>>>> +{
>>>> +       struct device *dev = container_of(kobj, struct device, kobj);
>>>> +       struct led_classdev *led_cdev = dev_get_drvdata(dev);
>>>> +
>>>> +       if (attr == &dev_attr_brightness.attr)
>>>> +               return attr->mode;
>>>> +       if (attr == &dev_attr_max_brightness.attr)
>>>> +               return attr->mode;
>>>> +       if (attr == &dev_attr_pattern.attr && led_cdev->pattern_set)
>>>> +               return attr->mode;
>>>> +
>>>> +       return 0;
>>>> +}
>>
>>
>>>>    #ifdef CONFIG_LEDS_TRIGGERS
>>>>    static DEVICE_ATTR(trigger, 0644, led_trigger_show, led_trigger_store);
>>>>    static struct attribute *led_trigger_attrs[] = {
>>>> @@ -88,11 +205,13 @@ static ssize_t max_brightness_show(struct device
>>>> *dev,
>>>>    static struct attribute *led_class_attrs[] = {
>>>>           &dev_attr_brightness.attr,
>>>>           &dev_attr_max_brightness.attr,
>>>> +       &dev_attr_pattern.attr,
>>>>           NULL,
>>>>    };
>>>>
>>>>    static const struct attribute_group led_group = {
>>>>           .attrs = led_class_attrs,
>>>> +       .is_visible = led_class_attrs_mode,
>>
>>
>> This should not be needed if we'll validate pattern ops
>> in led_classdev_register().
> 
> I am afraid we can not remove it. If the driver did not supply
> pattern_set/get/clear, we should not still show the pattern interfaces
> for userspace.

You're right.

-- 
Best regards,
Jacek Anaszewski

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