On Tue, Jul 23, 2019 at 5:21 PM Tony Lindgren <tony@xxxxxxxxxxx> wrote: > > For many years omap variants have been setting the runtime PM > autosuspend delay to -1 to prevent unsafe policy with lossy first > character on wake-up. The user must specifically enable the timeout > for UARTs if desired. > > We must not enable the workaround for serdev devices though. It leads > into UARTs not idling if no serdev devices are loaded and there is no > sysfs entry to configure the UART in that case. And this means that > my PM may not work unless the serdev modules are loaded. > > We can detect a serdev device being configured based on a dts child > node, and we can simply skip the workround in that case. And the > serdev driver can idle the port during runtime when suitable if an > out-of-band wake-up GPIO line exists for example. > > Let's also add some comments to the workaround while at it. This seems to help some of the stability issues I am seeing on the DM3730 UART2 running Bluetooth at 3000000 baud. Does it make sense to backport this to the stable kernels? adam > > Cc: Johan Hovold <johan@xxxxxxxxxx> > Signed-off-by: Tony Lindgren <tony@xxxxxxxxxxx> > --- > drivers/tty/serial/8250/8250_omap.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c > --- a/drivers/tty/serial/8250/8250_omap.c > +++ b/drivers/tty/serial/8250/8250_omap.c > @@ -1234,7 +1234,16 @@ static int omap8250_probe(struct platform_device *pdev) > > device_init_wakeup(&pdev->dev, true); > pm_runtime_use_autosuspend(&pdev->dev); > - pm_runtime_set_autosuspend_delay(&pdev->dev, -1); > + > + /* > + * Disable runtime PM until autosuspend delay unless specifically > + * enabled by the user via sysfs. This is the historic way to > + * prevent an unsafe default policy with lossy characters on wake-up. > + * For serdev devices this is not needed, the policy can be managed by > + * the serdev driver. > + */ > + if (!of_get_available_child_count(pdev->dev.of_node)) > + pm_runtime_set_autosuspend_delay(&pdev->dev, -1); > > pm_runtime_irq_safe(&pdev->dev); > pm_runtime_enable(&pdev->dev); > -- > 2.21.0
