Messages in this thread | | | From | Chris Chiu <> | Date | Wed, 4 Sep 2019 12:38:24 +0800 | Subject | Re: Tweak I2C SDA hold time on GemniLake to make touchpad work |
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On Tue, Sep 3, 2019 at 8:03 PM Jarkko Nikula <jarkko.nikula@linux.intel.com> wrote: > > Hi Chris > > On 9/3/19 11:18 AM, Mika Westerberg wrote: > > +Jarkko > > > > On Tue, Sep 03, 2019 at 04:10:27PM +0800, Chris Chiu wrote: > >> Hi, > >> > >> We're working on the acer Gemnilake laptop TravelMate B118-M for > >> touchpad not working issue. The touchpad fails to bring up and the > >> i2c-hid ouput the message as follows > >> [ 8.317293] i2c_hid i2c-ELAN0502:00: hid_descr_cmd failed > >> We tried on latest linux kernel 5.3.0-rc6 and it reports the same. > >> > >> We then look into I2C signal level measurement to find out why. > >> The following is the signal output from LA for the SCL/SDA. > >> https://imgur.com/sKcpvdo > >> The SCL frequency is ~400kHz from the SCL period, but the SDA > >> transition is quite weird. Per the I2C spec, the data on the SDA line > >> must be stable during the high period of the clock. The HIGH or LOW > >> state of the data line can only change when the clock signal on the > >> SCL line is LOW. The SDA period span across 2 SCL high, I think > >> that's the reason why the I2C read the wrong data and fail to initialize. > >> > >> Thus, we treak the SDA hold time by the following modification. > >> > >> --- a/drivers/mfd/intel-lpss-pci.c > >> +++ b/drivers/mfd/intel-lpss-pci.c > >> @@ -97,7 +97,8 @@ static const struct intel_lpss_platform_info bxt_uart_info = { > >> }; > >> > >> static struct property_entry bxt_i2c_properties[] = { > >> - PROPERTY_ENTRY_U32("i2c-sda-hold-time-ns", 42), > >> + PROPERTY_ENTRY_U32("i2c-sda-hold-time-ns", 230), > >> PROPERTY_ENTRY_U32("i2c-sda-falling-time-ns", 171), > >> PROPERTY_ENTRY_U32("i2c-scl-falling-time-ns", 208), > >> { }, > >> > >> The reason why I choose sda hold time is by the Table 10 of > >> https://www.nxp.com/docs/en/user-guide/UM10204.pdf, the device > >> must provide a hold time at lease 300ns and and 42 here is relatively > >> too small. The signal measurement result for the same pin on Windows > >> is as follows. > >> https://imgur.com/BtKUIZB > >> Comparing to the same result running Linux > >> https://imgur.com/N4fPTYN > >> > >> After applying the sda hold time tweak patch above, the touchpad can > >> be correctly initialized and work. The LA signal is shown as down below. > >> https://imgur.com/B3PmnIp > >> > Could you try does attached patch work for you? > > It's from last year for another related issue but there platform was > actually Apollo Lake instead of Gemini Lake but anyway it was found out > that Windows uses different timing parameters than Linux on Gemini Lake. > > I didn't take patch forward back then due known Gemini Lake machines > were working with the Broxton I2C timing parameters but now it's time if > attached patch fixes the issue on your machine. > > Patch is from top of v5.3-rc7 but should probably apply also to older > kernels. > > -- > Jarkko
Thanks, Jarkko, the patche works on my acer laptops.
Chris
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