linux-kernel - Re: [PATCH] platform/x86: dell-privacy: Add support for new privacy driver

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Message-ID: <544bc53f-c260-9e46-15a9-2ec2ea41343c@redhat.com>
Date:   Thu, 12 Nov 2020 16:55:07 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     "Limonciello, Mario" <Mario.Limonciello@...l.com>,
        "Enrico Weigelt, metux IT consult" <lkml@...ux.net>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        "Yuan, Perry" <Perry.Yuan@...l.com>
Cc:     "mgross@...ux.intel.com" <mgross@...ux.intel.com>,
        "pali@...nel.org" <pali@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "platform-driver-x86@...r.kernel.org" 
        <platform-driver-x86@...r.kernel.org>
Subject: Re: [PATCH] platform/x86: dell-privacy: Add support for new privacy
 driver

Hi,

On 11/12/20 4:31 PM, Limonciello, Mario wrote:
>>> Pressing the mute key activates a time delayed circuit to physically cut
>>> off the mute.  The LED is in the same circuit, so it reflects the true
>>> state of the HW mute.  The reason for the EC "ack" is so that software
>>> can first invoke a SW mute before the HW circuit is cut off.  Without SW
>>> cutting this off first does not affect the time delayed muting or status
>>> of the LED but there is a possibility of a "popping" noise leading to a
>>> poor user experience.
>>
>> how long is that timeout ?
> 
> The exact duration is controlled by component selection in the circuit.
> Linux is typically able to respond faster than Windows in this case.
> 
>>
>>> Exposing as an LED device allows the codec drivers notification path to
>>> EC ACK to work.
>>
>> Which driver exactly ? Who's gonna access this LED ?
> 
> The flow is like this:
> 
> 1) User presses key.  HW does stuff with this key (timeout is started)
> 2) Event is emitted from FW
> 3) Event received by dell-privacy
> 4) KEY_MICMUTE emitted from dell-privacy
> 5) Userland picks up key and modifies kcontrol for SW mute
> 6) Codec kernel driver catches and calls ledtrig_audio_set, like this:
> 
> ledtrig_audio_set(LED_AUDIO_MICMUTE, rt715->micmute_led ? LED_ON : LED_OFF);
> 
> 7) If "LED" is set to on dell-privacy notifies ec, and timeout is cancelled,
> HW mic mute activated.
> 
> Again, if anything in this flow doesn't happen HW mic mute is still activated,
> just will take longer (for duration of timeout) and have popping noise.

Thank you, can we put this in a comment in the driver please ?

I guess this also means that the led_class device is just there to
catch the ledtrig_audio_set() call so that dell-firmware can tell the
EC that the sw-mute is done and that it can move ahead with the hw-mute.

While the real, physical LED is fully under hardware control, right ?

That should probably also be in the same comment in the driver
(feel free to re-use part of my wording for that if that helps).

Regards,

Hans



> 
>>
>>
>> --mtx
>>
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>> ---
>> Enrico Weigelt, metux IT consult
>> Free software and Linux embedded engineering
>> info@...ux.net -- +49-151-27565287