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    SubjectRe: [PATCH/RFC v9 02/19] Documentation: leds: Add description of LED Flash class extension
    Hi Sakari,

    Thanks for the review.

    On 12/03/2014 06:08 PM, Sakari Ailus wrote:
    > Hi Jacek,
    >
    > On Wed, Dec 03, 2014 at 05:06:37PM +0100, Jacek Anaszewski wrote:
    >> The documentation being added contains overall description of the
    >> LED Flash Class and the related sysfs attributes.
    >>
    >> Signed-off-by: Jacek Anaszewski <j.anaszewski@samsung.com>
    >> Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
    >> Cc: Bryan Wu <cooloney@gmail.com>
    >> Cc: Richard Purdie <rpurdie@rpsys.net>
    >> ---
    >> Documentation/leds/leds-class-flash.txt | 50 +++++++++++++++++++++++++++++++
    >> 1 file changed, 50 insertions(+)
    >> create mode 100644 Documentation/leds/leds-class-flash.txt
    >>
    >> diff --git a/Documentation/leds/leds-class-flash.txt b/Documentation/leds/leds-class-flash.txt
    >> new file mode 100644
    >> index 0000000..82e58b1
    >> --- /dev/null
    >> +++ b/Documentation/leds/leds-class-flash.txt
    >> @@ -0,0 +1,50 @@
    >> +
    >> +Flash LED handling under Linux
    >> +==============================
    >> +
    >> +Some LED devices support two modes - torch and flash. The modes are
    >> +supported by the LED class (see Documentation/leds/leds-class.txt)
    >> +and LED Flash class respectively.
    >> +
    >> +In order to enable support for flash LEDs CONFIG_LEDS_CLASS_FLASH symbol
    >> +must be defined in the kernel config. A flash LED driver must register
    >> +in the LED subsystem with led_classdev_flash_register to gain flash
    >> +capabilities.
    >> +
    >> +Following sysfs attributes are exposed for controlling flash led devices:
    >> +
    >> + - flash_brightness - flash LED brightness in microamperes (RW)
    >> + - max_flash_brightness - maximum available flash LED brightness (RO)
    >> + - flash_timeout - flash strobe duration in microseconds (RW)
    >> + - max_flash_timeout - maximum available flash strobe duration (RO)
    >> + - flash_strobe - flash strobe state (RW)
    >> + - flash_sync_strobe - one flash device can control more than one
    >> + sub-led; when this atrribute is set to 1
    >
    > s/atrribute/attribute/
    >
    >> + the flash led will be strobed synchronously
    >> + with the other one controlled by the same
    >> + device; flash timeout setting is inherited
    >> + from the led being strobed explicitly and
    >> + flash brightness setting of a sub-led's
    >> + being synchronized is used (RW)
    >
    > The flash brightness shouldn't be determined by the strobed LED. If this is
    > a property of the hardware, then be it, but in general no, it it shouldn't
    > be an interface requirement. I think this should just say that the strobe is
    > synchronised.

    I intended this to sound exactly as you laid it out above, but maybe it
    is obscure English. "and flash brightness setting of a sub-led >>>being
    synchronized<<< is used" - from my point of view the led being
    synchronized is the one that isn't strobed explicitly. But I'm ok with
    confining ourselves only to saying that strobe is synchronized.

    > How does the user btw. figure out which flash LEDs may be strobed
    > synchronously using the LED flash interface?

    The flash_sync_strobe argument is absent if synchronized strobe
    is not available for a LED. The driver defines this by setting
    newly added LED_DEV_CAP_COMPOUND flag.

    Best Regards,
    Jacek Anaszewski


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