linux-kernel - Re: Need some help on "Input: elantech - add LEN2146 to SMBus blacklist for ThinkPad L13 Gen2"

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Message-ID: <20210225093801.GA1008@ninjato>
Date:   Thu, 25 Feb 2021 10:38:01 +0100
From:   Wolfram Sang <wsa@...nel.org>
To:     Nikolai Kostrigin <nickel@...ealt.ru>
Cc:     linux-i2c@...r.kernel.org,
        "open list:HID CORE LAYER" <linux-input@...r.kernel.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Colin Ian King <colin.king@...onical.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: Need some help on "Input: elantech - add LEN2146 to SMBus
 blacklist for ThinkPad L13 Gen2"

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

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