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

[Jarkko Nikula <jarkko.nikula@linux.intel.com>]

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