Messages in this thread | | | Subject | Re: Tweak I2C SDA hold time on GemniLake to make touchpad work | From | Jarkko Nikula <> | Date | Wed, 4 Sep 2019 08:54:08 +0300 |
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On 9/4/19 7:38 AM, Chris Chiu wrote: > 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. > Thanks. I'll send the patch out with Cc'ing you. I took the freedom to add your Tested-by tag if you don't mind :-)
-- Jarkko
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