On 1/16/2015 9:25 PM, Andrew Lunn wrote: > On Fri, Jan 16, 2015 at 04:52:12PM +0200, Tomi Valkeinen wrote: >> Hi, >> >> On 15/01/15 01:15, Andrew Lunn wrote: >>> This patchset is a driver for the TI tlc59116 16 Channel i2c LED >>> driver. This driver is used on the Belkin WRT1900AC access point and >>> the C code is derived from code Belkin contributed to OpenWRT. >>> However it has been extensively re-written, and a device tree binding >>> added to replace platform data. >> >> We have a TLC59108 on one of our boards, and with a quick glance it >> looks about the same as TLC59116, except the amount of outputs. Vignesh >> wrote a driver for it and was about to send it for review. >> >> However, Vignesh implemented it as a PWM driver. We use it for LCD >> backlight (via pwm-backlight). >> >> I'm not very familiar with LED and PWM drivers, but doesn't implementing >> this as a LED driver prevent us from using it as a backlight? Whereas it >> looks like PWM can be used as a led via pwm-leds (I think). >> > Hi Tomi > > I've no idea about backlighting.... > > But the driver does fully implement brightness. So on my board: > > echo 128 > /sys/class/leds/wrt1900ac\:white\:wan/brightness > > will set that LED to 128/256 brightness. You have 255 steps of > brightness. > > The reason i did not model it as a PWM, is that it cannot fulfil the > PWM interface. The configure interface is: > > int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns); > > However with this device, you have no control over the period. It is > fixed, from a 97-kHz clock. All you can change is the duty as a ratio > between 0 and 256. There is the group PWM, where you do have control > over the period. But as the name implies, this PWM is shared for all > outputs, which is not what the PWM interface expects, it wants to be > able to control them individually. Also, it only has a range of 24 Hz > to 10.73 s. Again, i have no idea about backlights, but i suspect if > it is driven at 24Hz, i'm going to get a headache. > > The LED interface can be fully implemented. So that is what i have > done. I understand that period of TLC chip cannot be changed and hence cannot fully implement PWM interface. But, suppose I want to control brightness of an LCD screen, with your current design, my LCD driver can never can do something like: pwm_get(chip); pwm_update_brightness(); pwm_remove(); I will always have to rely on sysfs entries to control brightness. If the driver is implemented as pwm-backlight, then brightness can be controlled both via sysfs entries and pwm-core callbacks(in kernel). > > So i think modeling this as an LED driver is correct, and maybe you > need to implemented an led_bl.c driver? > But, as far as I understand, leds-pwm.c does almost similar function. Regards Vignesh R -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
