[systemd-devel] [PATCH] backlight: let the administrator override clamping

[Topi Miettinen]

On 01/17/15 12:03, David Herrmann wrote:
> Hi
> 
> On Sat, Jan 17, 2015 at 1:01 PM, Topi Miettinen <toiwoton at gmail.com> wrote:
>> On 01/17/15 11:38, David Herrmann wrote:
>>> Hi
>>>
>>> On Sat, Jan 17, 2015 at 12:28 PM, Topi Miettinen <toiwoton at gmail.com> wrote:
>>>> On my computer, the minimum brightness enforced by clamping in
>>>> backlight is too bright.
>>>
>>> How can 5% of the backlight be "too bright"? Can you give some
>>> information on your backlight device? (type, max_brightness,
>>> actual_brightness and so on).
>>
>> Well, my eyes start to hurt with level 1, 0 is OK. Max_brightness is 9,
>> actual_brightness always matches brightness. This is cheap old Acer
>> Aspire 8530 laptop with Mobility Radeon HD 3200, I don't know beyond
>> that what handles backlight.
> 
> Which backlight driver is active? acpi? Or the native radeon driver?

The device path is
/sys/devices/pci0000\:00/0000\:00\:01.0/0000\:01\:05.0/backlight/acpi_video0/brightness,
does that mean acpi?

-Topi

> 
> Thanks
> David
> 
>>>
>>> Btw., we use gnu-getopt_long() style arguments with two dashes. And we
>>> try to avoid negations in option names.
>>
>> Ok. How about --disable-clamping or --allow-low-brightness, or would you
>> have better ideas?
>>
>>>
>>> Thanks
>>> David
>>>
>>>> Add a new option to override clamping in unit file. While at it, describe
>>>> the clamping in documentation.
>>>> ---
>>>>  man/systemd-backlight at .service.xml | 23 +++++++++++++++++++++--
>>>>  src/backlight/backlight.c          | 11 ++++++-----
>>>>  2 files changed, 27 insertions(+), 7 deletions(-)
>>>>
>>>> diff --git a/man/systemd-backlight at .service.xml b/man/systemd-backlight at .service.xml
>>>> index 453afbf..26a2437 100644
>>>> --- a/man/systemd-backlight at .service.xml
>>>> +++ b/man/systemd-backlight at .service.xml
>>>> @@ -48,7 +48,17 @@
>>>>
>>>>          <refsynopsisdiv>
>>>>                  <para><filename>systemd-backlight at .service</filename></para>
>>>> -                <para><filename>/usr/lib/systemd/systemd-backlight</filename></para>
>>>> +                <cmdsynopsis>
>>>> +                        <command>systemd-backlight</command>
>>>> +                        <arg choice="plain">save</arg>
>>>> +                        <arg choice="opt"><replaceable>PATH</replaceable></arg>
>>>> +                </cmdsynopsis>
>>>> +                <cmdsynopsis>
>>>> +                        <command>systemd-backlight</command>
>>>> +                        <arg choice="plain">load</arg>
>>>> +                        <arg choice="opt"><replaceable>PATH</replaceable></arg>
>>>> +                        <arg choice="opt"><replaceable>-no-clamp</replaceable></arg>
>>>> +                </cmdsynopsis>
>>>>          </refsynopsisdiv>
>>>>
>>>>          <refsect1>
>>>> @@ -58,7 +68,16 @@
>>>>                  is a service that restores the display backlight
>>>>                  brightness at early boot and saves it at shutdown. On
>>>>                  disk, the backlight brightness is stored in
>>>> -                <filename>/var/lib/systemd/backlight/</filename>.</para>
>>>> +                <filename>/var/lib/systemd/backlight/</filename>. During
>>>> +                loading, unless option
>>>> +                <replaceable>-no-clamp</replaceable> is specified, the
>>>> +                brightness is clamped to at least value
>>>> +                <literal>1</literal> or 5% of maximum
>>>> +                brightness.</para>
>>>> +
>>>> +                <para><replaceable>PATH</replaceable> identifies the
>>>> +                display brightness control device. It is resolved by
>>>> +                udev.</para>
>>>>          </refsect1>
>>>>
>>>>          <refsect1>
>>>> diff --git a/src/backlight/backlight.c b/src/backlight/backlight.c
>>>> index 1271a66..a3f71e9 100644
>>>> --- a/src/backlight/backlight.c
>>>> +++ b/src/backlight/backlight.c
>>>> @@ -255,7 +255,7 @@ static void clamp_brightness(struct udev_device *device, char **value, unsigned
>>>>                          return;
>>>>                  }
>>>>
>>>> -                log_info("Saved brightness %s %s to %s.", old_value,
>>>> +                log_info("Saved brightness %s %s to %s (use -no-clamp to override).", old_value,
>>>>                           new_brightness > brightness ?
>>>>                           "too low; increasing" : "too high; decreasing",
>>>>                           *value);
>>>> @@ -272,8 +272,8 @@ int main(int argc, char *argv[]) {
>>>>          unsigned max_brightness;
>>>>          int r;
>>>>
>>>> -        if (argc != 3) {
>>>> -                log_error("This program requires two arguments.");
>>>> +        if (argc < 3 || argc > 4) {
>>>> +                log_error("This program requires two or three arguments.");
>>>>                  return EXIT_FAILURE;
>>>>          }
>>>>
>>>> @@ -389,8 +389,9 @@ int main(int argc, char *argv[]) {
>>>>                          log_error_errno(r, "Failed to read %s: %m", saved);
>>>>                          return EXIT_FAILURE;
>>>>                  }
>>>> -
>>>> -                clamp_brightness(device, &value, max_brightness);
>>>> +                /* Don't clamp brightness if asked */
>>>> +                if (!(argc == 4 && streq(argv[3], "-no-clamp")))
>>>> +                        clamp_brightness(device, &value, max_brightness);
>>>>
>>>>                  r = udev_device_set_sysattr_value(device, "brightness", value);
>>>>                  if (r < 0) {
>>>> --
>>>> 2.1.4
>>>>
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>>