[v2,1/7] serial: qcom-geni: fix premature receiver enable

The receiver should not be enabled until the port is opened so drop the
bogus call to start rx from the setup code which is shared with the
console implementation.

This was added for some confused implementation of hibernation support,
but the receiver must not be started unconditionally as the port may not
have been open when hibernating the system.

Fixes: 35781d8356a2 ("tty: serial: qcom-geni-serial: Add support for Hibernation feature")
Cc: stable@vger.kernel.org	# 6.2
Cc: Aniket Randive <quic_arandive@quicinc.com>
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
---
 drivers/tty/serial/qcom_geni_serial.c | 1 -
 1 file changed, 1 deletion(-)

On Tue, Oct 01, 2024 at 07:20:36PM GMT, Mukesh Kumar Savaliya wrote:
> Thanks Johan for the fixes.
> 
> On 10/1/2024 6:20 PM, Johan Hovold wrote:
> > The receiver should not be enabled until the port is opened so drop the
> > bogus call to start rx from the setup code which is shared with the
> > console implementation.
> > 
> > This was added for some confused implementation of hibernation support,
> > but the receiver must not be started unconditionally as the port may not
> > have been open when hibernating the system.
> > 
> > Fixes: 35781d8356a2 ("tty: serial: qcom-geni-serial: Add support for Hibernation feature")
> > Cc:stable@vger.kernel.org	# 6.2
> > Cc: Aniket Randive<quic_arandive@quicinc.com>
> > Signed-off-by: Johan Hovold<johan+linaro@kernel.org>
> > ---
> >   drivers/tty/serial/qcom_geni_serial.c | 1 -
> >   1 file changed, 1 deletion(-)
> > 
> > diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
> > index 6f0db310cf69..9ea6bd09e665 100644
> > --- a/drivers/tty/serial/qcom_geni_serial.c
> > +++ b/drivers/tty/serial/qcom_geni_serial.c
> > @@ -1152,7 +1152,6 @@ static int qcom_geni_serial_port_setup(struct uart_port *uport)
> >   			       false, true, true);
> >   	geni_se_init(&port->se, UART_RX_WM, port->rx_fifo_depth - 2);
> >   	geni_se_select_mode(&port->se, port->dev_data->mode);
> > -	qcom_geni_serial_start_rx(uport);
> Does it mean hibernation will break now ? Not sure if its tested with
> hibernation. I can see this call was added to port_setup specifically for
> hibernation but now after removing it, where is it getting fixed ?

Can you explain how you're testing hibernation and on which platform
this is done? I'd like to add this to my set of tests, but last time I
tested I couldn't find a platform where we survived the restore
processes (it's been a while though).

> I think RX will not be initialized after hibernation.

qcom_geni_serial_port_setup() is invoked in multiple places, how come
we don't perform this hibernation-specific operation in
qcom_geni_serial_sys_hib_resume()? (And why is it called hib_resume when
the kernel nomenclature for what it does is "restore"?)

Regards,
Bjorn

> >   	port->setup = true;
> >   	return 0;
> > -- 2.45.2

Hi,

On Tue, Oct 1, 2024 at 5:51 AM Johan Hovold <johan+linaro@kernel.org> wrote:
>
> The receiver should not be enabled until the port is opened so drop the
> bogus call to start rx from the setup code which is shared with the
> console implementation.
>
> This was added for some confused implementation of hibernation support,
> but the receiver must not be started unconditionally as the port may not
> have been open when hibernating the system.

Could you provide a motivation for your patch in the description? Is
patch needed for something (perhaps a future patch in the series)? Is
it fixing a bug? Does it save power? Is the call harmless but cleaner
to get rid of?


> Fixes: 35781d8356a2 ("tty: serial: qcom-geni-serial: Add support for Hibernation feature")
> Cc: stable@vger.kernel.org      # 6.2
> Cc: Aniket Randive <quic_arandive@quicinc.com>
> Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
> ---
>  drivers/tty/serial/qcom_geni_serial.c | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
> index 6f0db310cf69..9ea6bd09e665 100644
> --- a/drivers/tty/serial/qcom_geni_serial.c
> +++ b/drivers/tty/serial/qcom_geni_serial.c
> @@ -1152,7 +1152,6 @@ static int qcom_geni_serial_port_setup(struct uart_port *uport)
>                                false, true, true);
>         geni_se_init(&port->se, UART_RX_WM, port->rx_fifo_depth - 2);
>         geni_se_select_mode(&port->se, port->dev_data->mode);
> -       qcom_geni_serial_start_rx(uport);

FWIW, I found at least one thing that's broken by your patch. If you
enable kgdb (but _not_ "kgdboc_earlycon") and then add "kgdbwait" to
the kernel command line parameters then things will be broken after
your patch. You'll drop into the debugger but can't interact with it.
The "kgdboc_earlycon" path handles this because of
"qcom_geni_serial_enable_early_read()" but it doesn't seem like
there's anything that handles it for normal kgdb. If you drop in the
debugger later it'll probably work if you've got an "agetty" running
because that'll enable the RX path.


-Doug