linux-kernel - Re: [PATCH 1/2] serial: qcom-geni: fix opp vote on shutdown

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Message-ID: <ZLFk1Q0pTfYmB5EU@hovoldconsulting.com>
Date:   Fri, 14 Jul 2023 17:08:05 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
Cc:     Johan Hovold <johan+linaro@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-arm-msm@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Rajendra Nayak <quic_rjendra@...cinc.com>,
        Matthias Kaehlcke <mka@...omium.org>
Subject: Re: [PATCH 1/2] serial: qcom-geni: fix opp vote on shutdown

On Fri, Jul 14, 2023 at 04:29:08PM +0200, Konrad Dybcio wrote:
> On 14.07.2023 15:02, Johan Hovold wrote:
> > The operating-performance-point vote needs to be dropped when shutting
> > down the port to avoid wasting power by keeping resources like power
> > domains in an unnecessarily high performance state (e.g. when a UART
> > connected Bluetooth controller is not in use).
> > 
> > Fixes: a5819b548af0 ("tty: serial: qcom_geni_serial: Use OPP API to set clk/perf state")
> > Cc: stable@...r.kernel.org      # 5.9
> > Cc: Rajendra Nayak <quic_rjendra@...cinc.com>
> > Cc: Matthias Kaehlcke <mka@...omium.org>
> > Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
> > ---
> I don't know a whole lot about this subsystem, but the PM call has
> a pointer to uport which already contains this clock rate.. Is it
> zeroed out by the core before we reach it, which would prevent us
> from reusing it?

No, but this driver has other issues and I couldn't be arsed fixing them
before addressing this bug.

Specifically that uartclk variable can currently be set by userspace...

I'll fix that up next week.

Johan