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

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Message-ID: <YJ19LMLV1HXk6BMf@hatter.bewilderbeest.net>
Date:   Thu, 13 May 2021 14:25:32 -0500
From:   Zev Weiss <zev@...ilderbeest.net>
To:     Andrew Jeffery <andrew@...id.au>
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 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.

>
>However, given the existing behaviour it shouldn't be problematic?
>

"existing behaviour" referring to what here?


Thanks,
Zev