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Date: Thu, 2 May 2024 01:09:37 +0200
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Subject: Re: [PATCH v3 1/3] HID: i2c-hid: Rely on HID descriptor fetch to
 probe
To: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Jiri Kosina <jikos@kernel.org>, Dmitry Torokhov <dtor@chromium.org>,
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 Johan Hovold <johan+linaro@kernel.org>, linux-input@vger.kernel.org,
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 Lukasz Majczak <lma@chromium.org>
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On 5/1/24 9:09 PM, Dmitry Torokhov wrote:
> Is it possible for a device to be wedged so hard that it refuses to
> acknowledge the address?

A slave is allowed to not acknowledge if not able (e.g., "because it's 
performing some real time function"), but a slave that does not 
acknowledge its address is electrically indistinguishable from a 
disconnected device. In such case the device is impossible to detect 
through I2C operations, and neither smbus probe nor a "real" command 
will see it.

Any logic we have to silence missing devices will also silence entirely 
unresponsive or extremely non-cooperate devices. That is the price to 
pay for avoiding the log message unfortunately.

No other errors from the smbus probe or a real command would be related 
to device presence, and some of them even suggest a device is present 
but broken (arbitration loss, assuming no shorts).