linux-kernel - Re: [PATCH] media: rc: gpio-ir-recv: add QoS support for cpuidle system

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Date:   Wed, 16 Sep 2020 19:19:54 +0100
From:   Sean Young <sean@...s.org>
To:     Joakim Zhang <qiangqing.zhang@....com>
Cc:     "mchehab@...nel.org" <mchehab@...nel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>, Andy Duan <fugang.duan@....com>
Subject: Re: [PATCH] media: rc: gpio-ir-recv: add QoS support for cpuidle
 system

Hi Joakim,

On Wed, Sep 16, 2020 at 10:22:11AM +0000, Joakim Zhang wrote:
> 
> Hi Sean,
> 
> Thanks for your hint, I will send a V2 soon according to your suggestions.
> 
> We also have a concern, since you are a IR expert, may you can give us answers. With this patch, the first frame once press could not been decoded.
> AFAIK, IR protocols have not specify how may frames transmitting once press, is there ang criterion to decide this?
> 
> Is it possible that single frame transmitting once pressing? Per my understanding, it will transmit more than one frame.

So remotes send IR signals while a button is being pressed down. For the
remotes I've seen, when pressing a button a short amount of time will repeat
the IR message at least three times. This is a few times when I've tried
this, but by no means exhaustive of all remotes or protocols.

I think the question you are trying to answer is, if we miss the first
message, will we at least have another chance if the message is repeated?

So I think the message will be repeated, but the repeat message is not
enough for the nec protocol. The nec repeat is a shorter message which
does not carry any information apart from "last key still pressed":

https://www.sbprojects.net/knowledge/ir/nec.php

Thanks,

Sean