Re: Tweak I2C SDA hold time on GemniLake to make touchpad work

[Chris Chiu]

On Wed, Sep 4, 2019 at 1:54 PM Jarkko Nikula
<jarkko.nikula@xxxxxxxxxxxxxxx> wrote:
>
> On 9/4/19 7:38 AM, Chris Chiu wrote:
> > On Tue, Sep 3, 2019 at 8:03 PM Jarkko Nikula
> > <jarkko.nikula@xxxxxxxxxxxxxxx> 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

No problem. Thanks