linux-kernel - Re: [PATCH] Input: synaptics-rmi4 - retry reading SMBus version on resume

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Date:   Fri, 12 May 2023 14:36:30 -0500
From:   Jeffery Miller <jefferymiller@...gle.com>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Andrew Duggan <andrew@...gan.us>,
        Jonathan Denose <jdenose@...omium.org>, jdenose@...gle.com,
        Lyude Paul <lyude@...hat.com>, loic.poulain@...aro.org,
        benjamin.tissoires@...hat.com,
        Andrew Duggan <aduggan@...aptics.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Maximilian Luz <luzmaximilian@...il.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, linux-input@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Input: synaptics-rmi4 - retry reading SMBus version on resume

On Wed, May 10, 2023 at 3:06 PM Dmitry Torokhov
<dmitry.torokhov@...il.com> wrote:
>
>
> I am not really fond of adding random repeats in the code base. Andrew,
> do you know if the Synaptics device needs certain delay when switching
> to SMbus mode?
>
That's reasonable. It's true this is a sleep to workaround rmi_smbus'
expectation that
it is able to successfully read from the i801 i2c smbus addr 0x2c on resume
when it cannot.

I do not know why the i801 i2c addr 0x2c is not responding on resume.
Infrequently it won't respond on boot during the initial
psmouse_smbus_create_companion but that is less noticeable since
it will stay in ps/2 mode and just lack features.

I do know adding a sleep in-between the psmouse deactivate call
and rmi_smbus's attempts to read from the 0x2c addr allow it to
succeed on this machine. I do not know the details as to why however.

I can apply workarounds until the underlying issue can be
identified and properly resolved.

I can apply patches and provide any sort of debugging or extra information that
might be useful to anyone familiar with these devices.

The smbus controller in this particular machine is:
00:1f.3 SMBus [0c05]: Intel Corporation 8 Series/C220 Series Chipset
Family SMBus Controller [8086:8c22] (rev 04)

Perhaps there's some way to detect when the addr is available later
and have it trigger a new probe similar to how psmouse_smbus_notifier
is triggered when the i801 bus becomes available?

Thank You,
Jeff