linux-kernel - Re: [PATCH v4 1/2] serial: 8250_dw: make dw8250_set_termios as default set

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Message-ID: <20160902112106.GB21737@kuha.fi.intel.com>
Date:   Fri, 2 Sep 2016 14:21:06 +0300
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     gregkh@...uxfoundation.org, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Jiri Slaby <jslaby@...e.com>, guohanjun@...wei.com,
        xuwei5@...ilicon.com, graeme.gregory@...aro.org,
        z.liuxinliang@...ilicon.com, linux-acpi@...r.kernel.org
Subject: Re: [PATCH v4 1/2] serial: 8250_dw: make dw8250_set_termios as
 default set_termios callback

On Wed, Aug 31, 2016 at 03:07:56PM +0300, Heikki Krogerus wrote:
> Hi,
> 
> On Wed, Aug 31, 2016 at 11:29:11AM +0800, Kefeng Wang wrote:
> > Make dw8250_set_termios() handle all cases of dw8250_data->clk properly,
> > then we can safely use dw8250_set_termios() as the default set_termios
> > callback instead of serial8250_do_set_termios(), so do it.
> > 
> > Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
> > ---
> >  drivers/tty/serial/8250/8250_dw.c | 5 ++---
> >  1 file changed, 2 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
> > index 5c0c123..adecece 100644
> > --- a/drivers/tty/serial/8250/8250_dw.c
> > +++ b/drivers/tty/serial/8250/8250_dw.c
> > @@ -235,7 +235,7 @@ static void dw8250_set_termios(struct uart_port *p, struct ktermios *termios,
> >  	unsigned int rate;
> >  	int ret;
> >  
> > -	if (IS_ERR(d->clk) || !old)
> > +	if (IS_ERR_OR_NULL(d->clk) || !old)
> >  		goto out;
> 
> This part is fine, but...
> 
> >  	clk_disable_unprepare(d->clk);
> > @@ -308,13 +308,11 @@ static void dw8250_quirks(struct uart_port *p, struct dw8250_data *data)
> >  			p->serial_in = dw8250_serial_in32;
> >  			data->uart_16550_compatible = true;
> >  		}
> > -		p->set_termios = dw8250_set_termios;
> >  	}
> >  
> >  	/* Platforms with iDMA */
> >  	if (platform_get_resource_byname(to_platform_device(p->dev),
> >  					 IORESOURCE_MEM, "lpss_priv")) {
> > -		p->set_termios = dw8250_set_termios;
> >  		data->dma.rx_param = p->dev->parent;
> >  		data->dma.tx_param = p->dev->parent;
> >  		data->dma.fn = dw8250_idma_filter;
> > @@ -391,6 +389,7 @@ static int dw8250_probe(struct platform_device *pdev)
> >  	p->iotype	= UPIO_MEM;
> >  	p->serial_in	= dw8250_serial_in;
> >  	p->serial_out	= dw8250_serial_out;
> > +	p->set_termios	= dw8250_set_termios;
> 
> I'm a bit worried about this. If I remember correctly, we didn't set
> the set_termios hook by default in the past because somebody was using
> a type of clk that can't handle rate rounding and ended up using
> improper clock frequency for some baud rates. Unfortunately I can't
> remember who had that problem and on which platform.
> 
> On the other hand, I'm not sure if drivers should worry about things
> like that. This should be done the other way around. The platform
> with the problem should unset the p->set_termios hook in a quirk, but
> by default everybody would use dw8250_set_termios.

No comments... I would suggest we skip this for now. I don't think
it's necessary for Hisilicon Hip05 SoC support, so perhaps you can
just propose this change separately.


Thanks,

-- 
heikki