On Wed 02 Feb 03:03 PST 2022, Marijn Suijten wrote: > On 2022-01-28 18:50:42, Bjorn Andersson wrote: > > On Wed 27 Oct 16:19 CDT 2021, Marijn Suijten wrote: > > > > > Hi Bjorn, > > > > > > On 2021-10-22 10:25:35, Bjorn Andersson wrote: > > > > On Sat 09 Oct 21:39 PDT 2021, 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> > > > > > --- > > > > > > > > Any feedback on this? > > > > > > I asked in #linux-msm whether anything is wrong with the patterns, > > > since my Sony Discovery (sdm630 with a pm660l) blinks way quicker on a > > > pattern that's supposed to stay on for 1s and off for 1s: > > > > > > echo "0 1000 255 1000" > /sys/class/leds/rgb\:status/hw_pattern > > > > > > It however seems to be broken in the same way on an older version now > > > (this might be v9 or v8) which I don't remember to be the case. Can you > > > double-check if this is all working fine on your side? If so, I'll have > > > to find some time to debug it on my end. > > > > > > > I had missed the fact that LPG_RAMP_DURATION_REG is two registers for > > msg and lsb, for a total of 9 bits of duration. So what you saw was > > probably ticking at 232ms. > > > > Note though that the pattern uses the last time as "high pause", so I > > expect that you should have seen 232 ms of off, followed by 464ms of > > light. > > Visual inspection seems to confirm those numbers indeed! > > > I've fixed this for v11, both rejecting invalid input and writing out > > all 9 bits. > > Doesn't that 512ms limit, together with using only the last value for > hi_pause (and not the first value for lo_pause) force users to write > patterns in a certain way which is not easily conveyed to the caller > except by reading the comment in the driver? I'd guess lo_pause can be > used even if not in ping-pong mode, it should just hold at the first > value for the given duration? > > (That said hw_pattern is anyway already riddled with device-specific > information, such as only having one `delta_t` which functions as the > step size for every entry, and with the change above would need to be > sourced from another step that's not the first.) > Perhaps we should clarify the single delta_t by requiring all those delta_t to be the same, rather than ignoring their value. I.e. we make the ping-pong pattern: <value> <lopause+t> ... <value[N/2-1]> <t> <value[N/2]> <hipause+t> <value[N/2-1]> <t> ... <value> <t> And for non-ping-pong: <value> <lopause+t> <value> <t> ... <value> <t> <value> <hipause + t> What do you think? > Bit of a stretch, but perhaps worth noting anyway: should this be > written in documentation somewhere, together with pattern examples and > their desired outcome to function as testcases too? > There's a comment in lpg_pattern_set() where I tried to capture this. I don't think it's worth documenting the behavior/structure away from the driver. But let's make sure it's captured properly there. Regards, Bjorn
