On 2022-02-02 16:08:29, Bjorn Andersson wrote: > On Wed, Feb 2, 2022 at 2:04 PM Bjorn Andersson > <bjorn.andersson@xxxxxxxxxx> wrote: > > > > On Wed 02 Feb 03:18 PST 2022, Marijn Suijten wrote: > > > > > On 2022-01-28 16:54:29, Bjorn Andersson wrote: > > > > The Light Pulse Generator (LPG) is a PWM-block found in a wide range of > > > > PMICs from Qualcomm. These PMICs typically comes with 1-8 LPG instances, > > > > with their output being routed to various other components, such as > > > > current sinks or GPIOs. > > > > > > > > Each LPG instance can operate on fixed parameters or based on a shared > > > > lookup-table, altering the duty cycle over time. This provides the means > > > > for hardware assisted transitions of LED brightness. > > > > > > > > A typical use case for the fixed parameter mode is to drive a PWM > > > > backlight control signal, the driver therefor allows each LPG instance > > > > to be exposed to the kernel either through the LED framework or the PWM > > > > framework. > > > > > > > > A typical use case for the LED configuration is to drive RGB LEDs in > > > > smartphones etc, for which the driver support multiple channels to be > > > > ganged up to a MULTICOLOR LED. In this configuration the pattern > > > > generators will be synchronized, to allow for multi-color patterns. > > > > > > > > Signed-off-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx> > > > > > > Reviewed-by: Marijn Suijten <marijn.suijten@xxxxxxxxxxxxxx> > > > > > > There may still be some things to improve based on whether lo_pause > > > works in non-ping-pong mode - to alleviate the requirement for the first > > > delta_t to be at most 512ms - but this patch should not be delayed much > > > longer and that's perhaps for a followup patch. Same for my request for > > > documentation and examples which at the same time serve as some form of > > > tests to see if everything works as desired. > > > > > > > I've been considering lopause to be the value before we start the > > pattern, but I think you're right in that it denotes how long we should > > hold the first value. > > > > So I think it might make sense in the predefined "<value> <delay> <value> > > <delay>" scheme to use first <delay> as to calculate lo-pause. I think > > it has to be calculated, because the first value will iiuc be held > > for (lopause + 1) * delay ms. As mentioned in v10 that seems like a great idea, as long as we can carefully validate and communicate these numbers to the user; both through documentation and kernel error messages when values are ultimately rejected. Again, perhaps it might be better to postpone this to a separate patchset as to not block the use of LPG for backlights which is arguably more important than some fancy phone notification led patterns. > > > I also vaguely remember other (downstream) drivers to support more than > > > 512ms per step by (drastically?) changing PWM period, but not sure how > > > that worked again nor if it was reliable. > > > > > > > Thinking about it again, while 512 is the 9th bit, we should be able to > > represent [0..1023] with 9 bits... > > > > Sorry, my mind was elsewhere as I wrote that. [0..511] is what we got. Yes, 9 bits in total and BIT(8) being the highest settable ^^ - Marijn
