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

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Message-ID: <AS8PR04MB8404FAD25C9881FAD2754FB192569@AS8PR04MB8404.eurprd04.prod.outlook.com>
Date:   Fri, 30 Sep 2022 08:02:48 +0000
From:   Sherry Sun <sherry.sun@....com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.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 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().

Best Regards
Sherry

> --
>  i.
> 
> > Actually I've been thinking about any other workaround all afternoon,
>  seems no other good options to me till now. And after a further check, I
> think the original patch is not needed, as uart_add_one_port() won't open
> the tty device, it should be safe to global reset the non-console ports  after
> uart_add_one_port().
> >
> > Best Regards
> > Sherry
> >