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Reply-To: nickel@basealt.ru
Subject: Re: Need some help on "Input: elantech - add LEN2146 to SMBus
 blacklist for ThinkPad L13 Gen2"
From:   Nikolai Kostrigin <nickel@basealt.ru>
To:     linux-i2c@vger.kernel.org, lkml <linux-kernel@vger.kernel.org>,
        "open list:HID CORE LAYER" <linux-input@vger.kernel.org>
Cc:     "Gustavo A. R. Silva" <gustavoars@kernel.org>,
        Colin Ian King <colin.king@canonical.com>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        Benjamin Tissoires <benjamin.tissoires@redhat.com>,
        "jingle.wu" <jingle.wu@emc.com.tw>, Wolfram Sang <wsa@kernel.org>
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Organization: BaseALT
Message-ID: <fe31f6f8-6e38-2ed6-8548-6fa271bf36e9@basealt.ru>
Date:   Wed, 3 Mar 2021 15:48:00 +0300
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Hi,
resending this once again, hoping it wouldn't contain any HTML and
wouldn't be filtered by LKML.

03.03.2021 13:11, Nikolai Kostrigin пишет:
> Hi,
> 
> 25.02.2021 12:38, Wolfram Sang пишет:
>> Hi,
>>
>>> I had a preliminary discussion with Benjamin Tissoires and according to
>>> our agreement I repost it for wider audience.
>>> Blacklisting the device was decided to be a bad idea.
>>> But actually I managed to get touchpad totally operational via SMBus
>>> using a following hack:
>>>
>>> providing a parameter to i2c_i801 driver:
>>>
>>> modprobe i2c_i801 disable_features=0x2 (i.e. disable the block buffer).
>> So, from an I2C perspective, there are two things to mention here:
>>
>> a) I am in the process of extending the I2C core to allow block
>> transfers > 32 byte. This is a slow process, though, because we need to
>> pay attention to not break userspace ABI. If this is done *and* the i801
>> driver supports length > 32 bytes, too, then it would work natively. If
>> the i801 can do this, this is a question for Jean Delvare.
>>
>> b) I don't know Elantech HW but there are devices out there which allow
>> configuration for the block size. Something like a bit specifying if
>> block transfers > 32 are allowed. Or the SMBus version to support. Block
>> transfers > 32 are SMBus 3.0+ only. If your HW does not have that,
>> disabling SMBus is an option, too. Disabling it in the i801 driver is
>> too much of a hammer, I'd say.
>>
>> Hope this helps! Happy hacking,
>>
>>    Wolfram
> Thank you for the information, Wolfram!
> 
> Finally it turned out that the solution was near me from the very
> beginning, but I failed to check mainline code at that moment (which is
> now 5.11).
> Happily Jingle Wu has pointed me to a couple of  patches of his
> (co-authored by Dmitry Torokhov):
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/dtor/input.git/commit/?h=next&id=056115daede8d01f71732bc7d778fb85acee8eb6
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/dtor/input.git/commit/?h=next&id=e4c9062717feda88900b566463228d1c4910af6d
> 
> I applied those to 5.10.17 and trackpoint works like a charm.
> So I guess theese patches are worth being backported to the longterm
> 5.10 branch.
> I'm really sorry for the noise.
> 

-- 
Best regards,
Nikolai Kostrigin