Re: [RESEND #2] [PATCH v2] LEDS: Add output invertion option to backlight trigger

Andrew Morton
2011-01-06T21:05:51Z

On Thu, 9 Dec 2010 14:41:50 +0100
Janusz Krzysztofik <jkrzyszt@tis.icnet.pl> wrote:

> This patch extends the LED backlight tirgger driver with an option that allows
> for inverting the trigger output polarity.
>
> With the invertion option provided, I (ab)use the backlight trigger for
> driving a LED that indicates LCD display blank condtition on my Amstrad Delta
> videophone. Since the machine has no dedicated power LED, it was not possible
> to distinguish if the display was blanked, or the machine was turned off,
> without touching it.
>
> The invert sysfs control is patterned after a similiar function of the GPIO
> trigger driver.
>
> Created and tested against linux-2.6.36-rc5 on Amstrad Delta.
> Retested on linux-2.6.37-rc4.
>
> Signed-off-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
> Cc: Richard Purdie <rpurdie@rpsys.net>
> ---
>
> Resent because I still can't see any response received, while yet another
> merge window is going to pass away soon.
>
> Applies cleanly on top of 2.6.37-rc4, so no need for yet another refresh. Only
> tried to clean up the commit message slightly - maybe my English is not good
> enough to bother with, if not the code?
>
> v1 -> v2 changes:
> - improve some conditional expressions to be more readable; thanks to Ralph
> Corderoy (from e3-hacking) and Lars-Peter Clausen for their suggestions,
> - refresh against linux-2.6.36-rc5.
>
> drivers/leds/ledtrig-backlight.c | 60
> ++++++++++++++++++++++++++++++++++++---
> 1 file changed, 56 insertions(+), 4 deletions(-)
>
> diff -upr linux-2.6.36-rc5.orig/drivers/leds/ledtrig-backlight.c linux-2.6.36-rc5/drivers/leds/ledtrig-backlight.c
> --- linux-2.6.36-rc5.orig/drivers/leds/ledtrig-backlight.c 2010-09-24 15:35:13.000000000 +0200
> +++ linux-2.6.36-rc5/drivers/leds/ledtrig-backlight.c 2010-10-03 15:59:49.000000000 +0200
> @@ -26,6 +26,7 @@ struct bl_trig_notifier {
> int brightness;
> int old_status;
> struct notifier_block notifier;
> + unsigned invert;
> };
>
> static int fb_notifier_callback(struct notifier_block *p,
> @@ -36,23 +37,63 @@ static int fb_notifier_callback(struct n
> struct led_classdev *led = n->led;
> struct fb_event *fb_event = data;
> int *blank = fb_event->data;
> + int new_status = *blank ? BLANK : UNBLANK;
>
> switch (event) {
> case FB_EVENT_BLANK :
> - if (*blank && n->old_status == UNBLANK) {
> + if (new_status == n->old_status)
> + break;
> +
> + if ((n->old_status == UNBLANK) ^ n->invert) {
> n->brightness = led->brightness;
> led_set_brightness(led, LED_OFF);
> - n->old_status = BLANK;
> - } else if (!*blank && n->old_status == BLANK) {
> + } else {
> led_set_brightness(led, n->brightness);
> - n->old_status = UNBLANK;
> }
> +
> + n->old_status = new_status;
> +
> break;
> }
>
> return 0;
> }
>
> +static ssize_t bl_trig_invert_show(struct device *dev,
> + struct device_attribute *attr, char *buf)
> +{
> + struct led_classdev *led = dev_get_drvdata(dev);
> + struct bl_trig_notifier *n = led->trigger_data;
> +
> + return sprintf(buf, "%s\n", n->invert ? "yes" : "no");
> +}

I think this should show "0" or "1", to match the thing which the user
wrote here.

> +static ssize_t bl_trig_invert_store(struct device *dev,
> + struct device_attribute *attr, const char *buf, size_t num)
> +{
> + struct led_classdev *led = dev_get_drvdata(dev);
> + struct bl_trig_notifier *n = led->trigger_data;
> + unsigned invert;
> + int ret;
> +
> + ret = sscanf(buf, "%u", &invert);

Here we should use strict_strtoul() so the kernel correctly rejects
input of the form "42foo".

> + if (ret < 1) {
> + dev_err(dev, "invalid value\n");
> + return -EINVAL;
> + }

And here it would be better to disallow any input other than 0 or 1.
Because "2" makes no sense and who knows, some time in the future we
might *want* to permit 2.

So...

--- a/drivers/leds/ledtrig-backlight.c~leds-add-output-inversion-option-to-backlight-trigger-fix
+++ a/drivers/leds/ledtrig-backlight.c
@@ -65,7 +65,7 @@ static ssize_t bl_trig_invert_show(struc
struct led_classdev *led = dev_get_drvdata(dev);
struct bl_trig_notifier *n = led->trigger_data;

- return sprintf(buf, "%s\n", n->invert ? "yes" : "no");
+ return sprintf(buf, "%u\n", n->invert);
}

static ssize_t bl_trig_invert_store(struct device *dev,
@@ -73,16 +73,17 @@ static ssize_t bl_trig_invert_store(stru
{
struct led_classdev *led = dev_get_drvdata(dev);
struct bl_trig_notifier *n = led->trigger_data;
- unsigned invert;
+ unsigned long invert;
int ret;

- ret = sscanf(buf, "%u", &invert);
- if (ret < 1) {
- dev_err(dev, "invalid value\n");
+ ret = strict_strtoul(buf, 10, &invert);
+ if (ret < 0)
+ return ret;
+
+ if (invert > 1)
return -EINVAL;
- }

- n->invert = !!invert;
+ n->invert = invert;

/* After inverting, we need to update the LED. */
if ((n->old_status == BLANK) ^ n->invert)
_

Could you help test it please?

> +static DEVICE_ATTR(invert, 0644, bl_trig_invert_show, bl_trig_invert_store);

This new sysfs file should be documented. Where would be an
appropriate place for that? Documentation/leds-class.txt doesn't
mention a sysfs API at all.