From: Dmitry Torokhov <dmitry.torokhov@gmail.com>
To: Kenny Levinsen <kl@kl.wtf>
Cc: Jiri Kosina <jikos@kernel.org>,
Dmitry Torokhov <dtor@chromium.org>,
Benjamin Tissoires <benjamin.tissoires@redhat.com>,
Douglas Anderson <dianders@chromium.org>,
Hans de Goede <hdegoede@redhat.com>,
Maxime Ripard <mripard@kernel.org>,
Kai-Heng Feng <kai.heng.feng@canonical.com>,
Johan Hovold <johan+linaro@kernel.org>,
linux-input@vger.kernel.org, linux-kernel@vger.kernel.org,
Radoslaw Biernacki <rad@chromium.org>,
Lukasz Majczak <lma@chromium.org>
Subject: Re: [PATCH v3 1/3] HID: i2c-hid: Rely on HID descriptor fetch to probe
Date: Wed, 1 May 2024 12:09:17 -0700 [thread overview]
Message-ID: <ZjKTXaBrb1vs4har@google.com> (raw)
In-Reply-To: <26070c7a-4005-4bb4-b4af-779bfc415dea@kl.wtf>
On Wed, May 01, 2024 at 07:24:08AM +0200, Kenny Levinsen wrote:
> On 4/30/24 11:41 PM, Dmitry Torokhov wrote:
> > I actually believe there is. On Chromebooks we may source components
> > from several vendors and use them in our devices. The components
> > are electrically compatible with each other, have exactly the same
> > connector, and therefore interchangeable. Because of that at probe time
> > we do not quite know if the device is there at given address, or not
> > (i.e. the touchpad could be from a different vendor and listening on
> > another address) and we need to make a quick determination whether we
> > should continue with probe or not.
>
> Maybe I should clarify what I meant: All I2C operations start with the
> master writing the slave address to the bus. When a slave reads its own
> address off the bus, it pulls the data line low to ACK. If no device is
> present on the bus with the specified address, the line stays high which is
> a NACK. This means that on the bus level, we have a clear error condition
> specifically for no device with the specified address being present on the
> bus.
>
> Whether the operation used is a dummy read or our first actual write should
> not matter - if the address is not acknowledged, the device is not present
> (or able to talk I2C).
Is it possible for a device to be wedged so hard that it refuses to
acknowledge the address?
> The problem lies in whether this "no device present
> on bus" error is reported clearly to us: Some drivers use -ENXIO
> specifically for this, some use it also for NACKs on written data, some
> report it but use other return codes for it, etc.
>
> Even if we stick to the smbus probe in the long run, if we get to the point
> where we can rely on the error codes from I2C drivers we would be able to
> correctly log and propagate other error classes like bus errors or I2C
> driver issues which are all currently silenced as "nothing at address" by
> the smbus probe.
I think this depends on the answer to the question above. If there is
potential that the chip may stop responding, I still see benefit in
differentiating initial "soft touch" poke vs. hard errors once we
established that there is/was a device and it started misbehaving.
Thanks.
--
Dmitry
next prev parent reply other threads:[~2024-05-01 19:09 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-26 22:47 [PATCH v3 0/3] HID: i2c-hid: Probe and wake device with HID descriptor fetch Kenny Levinsen
2024-04-26 22:47 ` [PATCH v3 1/3] HID: i2c-hid: Rely on HID descriptor fetch to probe Kenny Levinsen
2024-04-27 3:21 ` Dmitry Torokhov
2024-04-27 13:20 ` Kenny Levinsen
2024-04-30 21:41 ` Dmitry Torokhov
2024-05-01 5:24 ` Kenny Levinsen
2024-05-01 19:09 ` Dmitry Torokhov [this message]
2024-05-01 23:09 ` Kenny Levinsen
2024-04-26 22:47 ` [PATCH v3 2/3] HID: i2c-hid: Retry HID descriptor read to wake up STM devices Kenny Levinsen
2024-04-26 22:47 ` [PATCH v3 3/3] HID: i2c-hid: Align i2c_hid_set_power() retry with HID descriptor read Kenny Levinsen
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