From: Tony Lindgren <tony@atomide.com>
To: Johan Hovold <johan@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Andy Shevchenko <andriy.shevchenko@intel.com>,
Jiri Slaby <jirislaby@kernel.org>,
Vignesh Raghavendra <vigneshr@ti.com>,
linux-serial@vger.kernel.org, linux-omap@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/6] serial: 8250: Implement prep_tx for power management
Date: Fri, 24 Sep 2021 18:16:10 +0300 [thread overview]
Message-ID: <YU3ruj32L/iaZS1h@atomide.com> (raw)
In-Reply-To: <YU3kPHg2qLr//HEF@hovoldconsulting.com>
* Johan Hovold <johan@kernel.org> [210924 14:44]:
> On Thu, Sep 23, 2021 at 06:05:36PM +0300, Tony Lindgren wrote:
> > * Johan Hovold <johan@kernel.org> [210923 12:50]:
> > > On Tue, Sep 21, 2021 at 01:33:44PM +0300, Tony Lindgren wrote:
> > > > +static int serial8250_prep_tx(struct uart_port *port)
> > > > +{
> > > > + struct uart_8250_port *up = up_to_u8250p(port);
> > > > + struct device *dev = up->port.dev;
> > > > + int err;
> > > > +
> > > > + if (!(up->capabilities & UART_CAP_RPM))
> > > > + return 0;
> > > > +
> > > > + if (!pm_runtime_suspended(dev)) {
> > > > + pm_runtime_mark_last_busy(dev);
> > > > + return 0;
> > > > + }
> > > > +
> > > > + err = pm_request_resume(dev);
> > > > + if (err < 0) {
> > > > + dev_warn(dev, "prep_tx wakeup failed: %d\n", err);
> > > > + return err;
> > > > + }
> > >
> > > How is this supposed to work without a runtime PM usage-counter
> > > increment? What's to prevent the port from suspending again while it's
> > > transmitting?
> >
> > Hmm yeah we should at pm_runtime_get() and pm_runtime_put() to write()
> > unless serial8250_rpm_get() and serial8250_rpm_put() are doing it.
>
> If you do the put after just buffering the data it doesn't really solve
> anything.
Right, sounds like we currently rely on the autosuspend_timeout
there.
> > Or pair prep with finish and deal with the usage count there.
>
> Problem is where to call it from. How do you tell the device is done
> transmitting? And how should we deal with flow control? Etc.
Maybe if the device driver needs to call uart_start() also from runtime
PM idle function and if no data allow suspend. Then if there is
more data, uart_write() calls uart_start() again, device wakes up
and so on.
Regards,
Tony
next prev parent reply other threads:[~2021-09-24 15:16 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-21 10:33 [PATCH 0/6] Get rid of pm_runtime_irq_safe() for 8250_omap Tony Lindgren
2021-09-21 10:33 ` [PATCH 1/6] n_tty: Start making use of -EAGAIN returned from process_output_block() Tony Lindgren
2021-09-21 11:58 ` Andy Shevchenko
2021-09-21 10:33 ` [PATCH 2/6] tty: n_gsm: Don't ignore write return value in gsmld_output() Tony Lindgren
2021-09-21 10:33 ` [PATCH 3/6] serial: core: Add new prep_tx for power management Tony Lindgren
2021-09-23 12:45 ` Johan Hovold
2021-09-23 15:02 ` Tony Lindgren
2021-09-24 14:37 ` Johan Hovold
2021-09-24 15:09 ` Tony Lindgren
2021-09-27 14:05 ` Johan Hovold
2021-09-21 10:33 ` [PATCH 4/6] serial: 8250: Implement " Tony Lindgren
2021-09-23 12:49 ` Johan Hovold
2021-09-23 15:05 ` Tony Lindgren
2021-09-24 14:44 ` Johan Hovold
2021-09-24 15:16 ` Tony Lindgren [this message]
2021-09-21 10:33 ` [PATCH 5/6] serial: 8250_omap: Require a valid wakeirq for deeper idle states Tony Lindgren
2021-09-21 10:33 ` [PATCH 6/6] serial: 8250_omap: Drop the use of pm_runtime_irq_safe() Tony Lindgren
2021-09-21 12:03 ` [PATCH 0/6] Get rid of pm_runtime_irq_safe() for 8250_omap Andy Shevchenko
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