linux-kernel - RE: [PATCH] Revert "serial: fsl_lpuart: Reset prior to registration"

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Date:   Fri, 30 Sep 2022 15:59:00 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Sherry Sun <sherry.sun@....com>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Lukas Wunner <lukas@...ner.de>,
        linux-serial <linux-serial@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH] Revert "serial: fsl_lpuart: Reset prior to
 registration"

On Fri, 30 Sep 2022, Sherry Sun wrote:
> > On Thu, 29 Sep 2022, Sherry Sun wrote:
> > 
> > > > > This reverts commit 60f361722ad2ae5ee667d0b0545d40c42f754daf.
> > > > >
> > > > > commit 60f361722ad2 ("serial: fsl_lpuart: Reset prior to
> > > > > registration") causes the lpuart console cannot work any more.
> > > > > Since the console is registered in the uart_add_one_port(), the
> > > > > driver cannot identify the console port before call
> > > > > uart_add_one_port(), which causes all the uart ports including the
> > > > > console port will be global
> > > > reset.
> > > > > So need to revert this patch to avoid breaking the lpuart console.
> > > > >
> > > > > Signed-off-by: Sherry Sun <sherry.sun@....com>
> > > > > ---
> > > > >  drivers/tty/serial/fsl_lpuart.c | 10 +++++-----
> > > > >  1 file changed, 5 insertions(+), 5 deletions(-)
> > > > >
> > > > > diff --git a/drivers/tty/serial/fsl_lpuart.c
> > > > > b/drivers/tty/serial/fsl_lpuart.c index 67fa113f77d4..7da46557fcb3
> > > > > 100644
> > > > > --- a/drivers/tty/serial/fsl_lpuart.c
> > > > > +++ b/drivers/tty/serial/fsl_lpuart.c
> > > > > @@ -2722,10 +2722,6 @@ static int lpuart_probe(struct
> > > > > platform_device
> > > > *pdev)
> > > > >  		handler = lpuart_int;
> > > > >  	}
> > > > >
> > > > > -	ret = lpuart_global_reset(sport);
> > > > > -	if (ret)
> > > > > -		goto failed_reset;
> > > > > -
> > > >
> > > > So the problem with this being so early is uart_console() in
> > > > lpuart_global_reset() that doesn't detect a console because
> > > > sport->cons is not yet assigned? Couldn't that be worked around
> > differently?
> > > >
> > > > Or is there something else in addition to that I'm missing?
> > > >
> > > Hi Ilpo,
> > >
> > > Yes, the root cause of the console cannot work after apply the commit
> > > 60f361722ad2 ("serial: fsl_lpuart: Reset prior to registration") is
> > > lpuart_global_reset() cannot identify the console port, so reset all
> > > uart ports.
> > 
> > This didn't answer my question. Is the main cause just lacking the ->cons
> > from sport at this point which, I guess, could be just assigned from lpuart_reg
> > similar to what uart_add_one_port() does before calling to reset?
> > 
> 
> Hi Ilpo,
> 
> Actually not only the (port)->cons need to be assigned, but also to get the right (port)->cons->index.
> 23 #define uart_console(port) \
> 24     ((port)->cons && (port)->cons->index == (port)->line)
> 
> The (port)->cons is assigned in uart_add_one_port(), quite simple.
> 3076     uport->cons = drv->cons;
> 
> But the (port)->cons->index is not that easy to get in lpuart driver, 
> now the value is assigned by calling register_console() from 
> uart_configure_port(). 

I've some skepticism to this claim. I now played with 8250 myself and 
confirmed it does have non-NULL ->cons for the console ports before 
to calls to uart_add_one_port() and index is setup up correctly for cons
too!

The reason for the cons being setup is this being done in 
univ8250_console_setup():

	/* link port to console */
	port->cons = co;

(which I think could be easily be done in lpuart_console_setup() too).

-- 
 i.