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

[Topi Miettinen]

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.

> 
> 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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