Re: [PATCH] serial: 8250_omap: Set the console genpd always on if no console suspend

[Kevin Hilman <khilman@kernel.org>]

Thomas Richard <thomas.richard@bootlin.com> writes:

> If the console suspend is disabled, the genpd of the console shall not
> be powered-off during suspend.
> Set the flag GENPD_FLAG_ALWAYS_ON to the corresponding genpd during
> suspend, and restore the original value during the resume.
>
> Signed-off-by: Thomas Richard <thomas.richard@bootlin.com>

Hmm, this patch got merged upstream (commit 68e6939ea9ec) even after
disagreements about the approach.

Even worse, it actually causes a crash during suspend on platforms that
don't use PM domains (like AM335x Beaglebone Black.)

Details on why this crashes below.

Thomas, could you please submit a revert for this (with a Fixes: tag)
and then follow up with the approach as discussed later in this thread?

> ---
>  drivers/tty/serial/8250/8250_omap.c | 33 ++++++++++++++++++++++++-----
>  1 file changed, 28 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
> index ca972fd37725..91a483dc460c 100644
> --- a/drivers/tty/serial/8250/8250_omap.c
> +++ b/drivers/tty/serial/8250/8250_omap.c
> @@ -27,6 +27,7 @@
>  #include <linux/pm_wakeirq.h>
>  #include <linux/dma-mapping.h>
>  #include <linux/sys_soc.h>
> +#include <linux/pm_domain.h>
>  
>  #include "8250.h"
>  
> @@ -114,6 +115,12 @@
>  /* RX FIFO occupancy indicator */
>  #define UART_OMAP_RX_LVL		0x19
>  
> +/*
> + * Copy of the genpd flags for the console.
> + * Only used if console suspend is disabled
> + */
> +static unsigned int genpd_flags_console;
> +
>  struct omap8250_priv {
>  	void __iomem *membase;
>  	int line;
> @@ -1617,6 +1624,7 @@ static int omap8250_suspend(struct device *dev)
>  {
>  	struct omap8250_priv *priv = dev_get_drvdata(dev);
>  	struct uart_8250_port *up = serial8250_get_port(priv->line);
> +	struct generic_pm_domain *genpd = pd_to_genpd(dev->pm_domain);

This genpd ptr will be NULL on am335x, and any other legacy platforms
that don't use PM domains, and then...

>  	int err = 0;
>  
>  	serial8250_suspend_port(priv->line);
> @@ -1627,8 +1635,19 @@ static int omap8250_suspend(struct device *dev)
>  	if (!device_may_wakeup(dev))
>  		priv->wer = 0;
>  	serial_out(up, UART_OMAP_WER, priv->wer);
> -	if (uart_console(&up->port) && console_suspend_enabled)
> -		err = pm_runtime_force_suspend(dev);
> +	if (uart_console(&up->port)) {
> +		if (console_suspend_enabled)
> +			err = pm_runtime_force_suspend(dev);
> +		else {
> +			/*
> +			 * The pd shall not be powered-off (no console suspend).
> +			 * Make copy of genpd flags before to set it always on.
> +			 * The original value is restored during the resume.
> +			 */
> +			genpd_flags_console = genpd->flags;
> +			genpd->flags |= GENPD_FLAG_ALWAYS_ON;

... BOOM.

> +		}
> +	}
>  	flush_work(&priv->qos_work);
>  
>  	return err;

Kevin