On Tue, May 8, 2018 at 11:47 PM, Daniel Drake <drake@xxxxxxxxxxxx> wrote: > On Tue, May 8, 2018 at 8:31 AM, Jarkko Nikula > <jarkko.nikula@xxxxxxxxxxxxxxx> wrote: >>> Some update, we can make the touchpad work by simply modifying the >>> clk_rate of spt_i2c_info from 120000000 to 133000000 in intel-lpss-pci.c for >>> specific PCI ID 8086:a368 ~ a36a (CoffeeLake). Is the clock setting different >>> for the CoffeeLake series? >>> >> Hmm.. at quick look it looks like to be 133 MHz but I want to double check first from other specs. I'm also wondering why it results 600 kHz instead of expected 133/120 * 400 kHz = 443 kHz. Need to check timing parameters too. > > Thanks for looking at this. I believe we tried 133MHz just because > some other platforms in the file have the clock at that speed. > > In the original/shipped setup, the scope shows the SDA clock is > running at ~635kHz (rather than the intended 400kHz) and the debug > logs from the kernel producing that waveform shows that HCNT=105 and > LCNT=191 > > 105+191=296 parent clock ticks per cycle > > At 635kHz, a single clock cycle is 1575ns. What is the speed of the > parent clock if it ticks 296 times in 1575ns? I calculate this to be > 187960000Hz and further experiments indicate that clk_rate=187960000 > also makes the touchpad work. Unfortunately we don't have easy access > to the scope to measure the effect on the waveform. > > Also through experimentation we tried i2c-sda-falling-time-ns=400ns > (increasing from the default of 300ns) in order to make the HCNT > increase to 117. This also makes the touchpad work. > Report from guys who can access scope. If i2c-sda-falling-time-ns=400ns , HCNT increase to 117, the SCL high duration is 576ns as follows https://pasteboard.co/HkwERvP.png The original SCL high duration (HCNT = 105, 120MHz) is as follows https://pasteboard.co/HkwFxgY.png So the HCNT does affect but per this HCNT/LCNT value, just not 400kHz as expected. Any suggestion? > Please let us know if we can help further in finding an upstream fix > for this issue. > > Thanks > Daniel -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
