linux-kernel - Re: [PATCH V4 1/4] arm64: dts: sc7180: Add wakeup support over UART RX

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Message-ID: <20200903171711.GL3419728@google.com>
Date:   Thu, 3 Sep 2020 10:17:11 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     satya priya <skakit@...eaurora.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        gregkh@...uxfoundation.org, Andy Gross <agross@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, akashast@...eaurora.org,
        rojay@...eaurora.org, msavaliy@....qualcomm.com
Subject: Re: [PATCH V4 1/4] arm64: dts: sc7180: Add wakeup support over UART
 RX

On Thu, Sep 03, 2020 at 08:34:55PM +0530, satya priya wrote:
> Add the necessary pinctrl and interrupts to make UART wakeup capable.
> 
> If QUP function is selected in sleep state, UART RTS/RFR is pulled high
> during suspend and BT SoC not able to send wakeup bytes. So, configure
> GPIO mode in sleep state to keep it low during suspend.
> 
> Signed-off-by: satya priya <skakit@...eaurora.org>
> Reviewed-by: Akash Asthana <akashast@...eaurora.org>

One more doubt: does it actually make sense/is it safe to add the
sleep config for all UARTs in the SoC file? I wonder if there could
be undesired behavior (like noise on TX or RTS looking active to the
other side) without the corresponding pinconf in the board file. If
the pinconf is needed to avoid unexpected behavior then it is better
to change the muxing in the board file to have a sane default
configuration in the SoC .dtsi.

>From a quick grep it seems that most SoCs don't specify a sleep config
for their UART pins and some boards add it in their DT.