linux-kernel - Re: [PATCH v12 1/1] serial: core: Start managing serial controllers to enable runtime PM

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Date:   Mon, 5 Jun 2023 15:24:47 +0300
From:   Tony Lindgren <tony@...mide.com>
To:     Chen-Yu Tsai <wenst@...omium.org>
Cc:     John Ogness <john.ogness@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...el.com>,
        Dhruva Gole <d-gole@...com>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        Johan Hovold <johan@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Vignesh Raghavendra <vigneshr@...com>,
        linux-omap@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
        Nícolas F. R. A. Prado 
        <nfraprado@...labora.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v12 1/1] serial: core: Start managing serial controllers
 to enable runtime PM

* Chen-Yu Tsai <wenst@...omium.org> [230605 11:34]:
> On Mon, Jun 5, 2023 at 2:15 PM Tony Lindgren <tony@...mide.com> wrote:
> > diff --git a/drivers/tty/serial/8250/8250_mtk.c b/drivers/tty/serial/8250/8250_mtk.c
> > --- a/drivers/tty/serial/8250/8250_mtk.c
> > +++ b/drivers/tty/serial/8250/8250_mtk.c
> > @@ -425,11 +439,10 @@ mtk8250_set_termios(struct uart_port *port, struct ktermios *termios,
> >  static int __maybe_unused mtk8250_runtime_suspend(struct device *dev)
> >  {
> >         struct mtk8250_data *data = dev_get_drvdata(dev);
> > -       struct uart_8250_port *up = serial8250_get_port(data->line);
> >
> >         /* wait until UART in idle status */
> >         while
> > -               (serial_in(up, MTK_UART_DEBUG0));
> > +               (mtk8250_read(data, MTK_UART_DEBUG0));
> 
> I believe it still gets stuck here sometimes.

Hmm so maybe you need to mtk8250_write(data, 0, MTK_UART_RATE_FIX) in
probe before pm_runtime_resume_and_get() that enables the baud clock?
That's something I changed, so maybe it messes up things.

Looking at the 8250_mtk git log, it's runtime PM functions seem to only
currently manage the baud clock so register access should be doable
without runtime PM resume?

> With your earlier patch, it could get through registering the port, and
> the console would show
> 
>     11002000.serial: ttyS0 at MMIO 0x11002000 (irq = 240, base_baud =
> 1625000) is a ST16650V2
> 
> for the console UART.

OK

> Angelo mentioned that we should be using SLEEP_REQ/SLEEP_ACK registers
> in the MTK UART hardware.
> 
> I tried reworking it into your patch here, but it causes issues with the
> UART-based Bluetooth on one of my devices. After the UART runtime suspends
> and resumes, something is off and causes the transfers during Bluetooth
> init to become corrupt.
> 
> I'll try some more stuff, but the existing code seems timing dependent.
> If I add too many printk statements to the runtime suspend/resume
> callbacks, things seem to work. One time I even ended up with broken
> UARTs but otherwise booted up the system.

Well another thing that now changes is that we now runtime suspend the
port at the end of the probe. What the 8250_mtk probe was doing earlier
it was leaving the port baud clock enabled, but runtime PM disabled
until mtk8250_do_pm() I guess.

Regards,

Tony