linux-kernel - Re: [PATCH] serial: 8250_dw: Fix runtime PM handling

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Message-ID: <20180928224056.GA10486@roeck-us.net>
Date:   Fri, 28 Sep 2018 15:40:56 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Phil Edworthy <phil.edworthy@...esas.com>,
        Greg KH <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org,
        Phil Edworthy <phil.edworthy@...esas.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Tony Lindgren <tony@...mide.com>
Subject: Re: [PATCH] serial: 8250_dw: Fix runtime PM handling

On Thu, May 10, 2018 at 03:13:56PM +0100, Phil Edworthy wrote:
> When using kgdb, you get an abort when accessing the UART registers.
> This is because the driver has already entered runtime PM and so turned
> off the bus clock needed to access the registers.
> 
> To fix this, set the capability indicating Runtime PM is active while idle.
> 

With this patch applied, I get the already reported traceback [1].
Obviously neither the promised revert [2] nor the presumed fix [3] made it
into the mainline Kernel.

Greg, can you please revert this patch ? If people don't care enough
to fix the problem, we should at least not have to suffer the consequences.

Thanks,
Guenter

> Signed-off-by: Phil Edworthy <phil.edworthy@...esas.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
>  drivers/tty/serial/8250/8250_dw.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
> index 0529b5cc094b..aff04f1de3a5 100644
> --- a/drivers/tty/serial/8250/8250_dw.c
> +++ b/drivers/tty/serial/8250/8250_dw.c
> @@ -576,6 +576,10 @@ static int dw8250_probe(struct platform_device *pdev)
>  	if (!data->skip_autocfg)
>  		dw8250_setup_port(p);
>  
> +#ifdef CONFIG_PM
> +	uart.capabilities |= UART_CAP_RPM;
> +#endif
> +
>  	/* If we have a valid fifosize, try hooking up DMA */
>  	if (p->fifosize) {
>  		data->dma.rxconf.src_maxburst = p->fifosize / 4;
> -- 
> 2.7.4

---
[1] https://www.spinics.net/lists/linux-serial/msg30379.html
[2] https://www.spinics.net/lists/linux-serial/msg30380.html
[3] https://www.spinics.net/lists/linux-serial/msg30757.html