linux-kernel - Re: [PATCH 2/3] serial: 8250_aspeed_vuart: initialize vuart->port in aspeed_vuart

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Message-Id: <6f530a9e-7d73-4ed8-90d4-29af079c0c2f@www.fastmail.com>
Date:   Fri, 14 May 2021 11:28:49 +0930
From:   "Andrew Jeffery" <andrew@...id.au>
To:     "Zev Weiss" <zev@...ilderbeest.net>
Cc:     "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Jeremy Kerr" <jk@...abs.org>, openbmc@...ts.ozlabs.org,
        "Jiri Slaby" <jirislaby@...nel.org>,
        "Joel Stanley" <joel@....id.au>, "Johan Hovold" <johan@...nel.org>,
        linux-serial@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-aspeed@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] serial: 8250_aspeed_vuart: initialize vuart->port in aspeed_vuart_probe()



On Fri, 14 May 2021, at 04:55, Zev Weiss wrote:
> On Wed, May 12, 2021 at 08:34:06PM CDT, Andrew Jeffery wrote:
> >
> >
> >On Mon, 10 May 2021, at 11:12, Zev Weiss wrote:
> >> Previously this had only been initialized if we hit the throttling path
> >> in aspeed_vuart_handle_irq(); moving it to the probe function is a
> >> slight consistency improvement and avoids redundant reinitialization in
> >> the interrupt handler.  It also serves as preparation for converting the
> >> driver's I/O accesses to use port->port.membase instead of its own
> >> vuart->regs.
> >>
> >> Signed-off-by: Zev Weiss <zev@...ilderbeest.net>
> >> ---
> >>  drivers/tty/serial/8250/8250_aspeed_vuart.c | 5 ++---
> >>  1 file changed, 2 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/tty/serial/8250/8250_aspeed_vuart.c
> >> b/drivers/tty/serial/8250/8250_aspeed_vuart.c
> >> index 9e8b2e8e32b6..249164dc397b 100644
> >> --- a/drivers/tty/serial/8250/8250_aspeed_vuart.c
> >> +++ b/drivers/tty/serial/8250/8250_aspeed_vuart.c
> >> @@ -349,11 +349,9 @@ static int aspeed_vuart_handle_irq(struct
> >> uart_port *port)
> >>  			struct aspeed_vuart *vuart = port->private_data;
> >>  			__aspeed_vuart_set_throttle(up, true);
> >>
> >> -			if (!timer_pending(&vuart->unthrottle_timer)) {
> >> -				vuart->port = up;
> >> +			if (!timer_pending(&vuart->unthrottle_timer))
> >>  				mod_timer(&vuart->unthrottle_timer,
> >>  					  jiffies + unthrottle_timeout);
> >> -			}
> >>
> >>  		} else {
> >>  			count = min(space, 256);
> >> @@ -511,6 +509,7 @@ static int aspeed_vuart_probe(struct platform_device *pdev)
> >>  		goto err_clk_disable;
> >>
> >>  	vuart->line = rc;
> >> +	vuart->port = serial8250_get_port(vuart->line);
> >
> >The documentation of serial8250_get_port() is somewhat concerning wrt
> >the use:
> >
> >https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/tty/serial/8250/8250_core.c?h=v5.13-rc1#n399
> 
> Hmm, good point -- though despite that comment it looks like there is 
> some existing code using it outside of suspend/resume callbacks (in 
> 8250_pci.c and 8250_pnp.c).  I'm not certain if those would necessarily 
> be considered good precedent to follow for this, but I don't see any 
> obvious better way of getting hold of the corresponding uart_8250_port 
> (or its port.membase).
> 
> I did receive a notification that Greg had added this series to his 
> tty-testing branch; not sure if that means he thinks it's OK or if it 
> just kind of slipped by unnoticed though.

Yeah, I just highlighted it in case anyone else wanted to weigh in.

Essentially I'm just deferring to Greg. If he's picked them up, great!

> 
> >
> >However, given the existing behaviour it shouldn't be problematic?
> >
> 
> "existing behaviour" referring to what here?

Well, we were poking at the registers through vuart->regs anyway.

So I don't think what you've done is any less correct.

Andrew