linux-kernel - Re: [PATCH tty-next v3 4/6] serial: 8250: Specify console context for rs485_start/stop

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Message-ID: <91303556-2632-49ca-be5d-9105c75b8a63@kernel.org>
Date: Wed, 30 Oct 2024 07:13:42 +0100
From: Jiri Slaby <jirislaby@...nel.org>
To: John Ogness <john.ogness@...utronix.de>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Petr Mladek <pmladek@...e.com>,
 Sergey Senozhatsky <senozhatsky@...omium.org>,
 Steven Rostedt <rostedt@...dmis.org>, Thomas Gleixner <tglx@...utronix.de>,
 Esben Haabendal <esben@...nix.com>, linux-serial@...r.kernel.org,
 linux-kernel@...r.kernel.org,
 Florian Fainelli <florian.fainelli@...adcom.com>,
 Broadcom internal kernel review list
 <bcm-kernel-feedback-list@...adcom.com>, Ray Jui <rjui@...adcom.com>,
 Scott Branden <sbranden@...adcom.com>,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 "Paul E. McKenney" <paulmck@...nel.org>, Arnd Bergmann <arnd@...db.de>,
 Stefan Wahren <wahrenst@....net>,
 Uwe Kleine-König <u.kleine-koenig@...libre.com>,
 Kevin Hilman <khilman@...libre.com>,
 Markus Schneider-Pargmann <msp@...libre.com>,
 Ronald Wahl <ronald.wahl@...itan.com>, Udit Kumar <u-kumar1@...com>,
 Griffin Kroah-Hartman <griffin@...ah.com>,
 Rengarajan S <rengarajan.s@...rochip.com>,
 Lino Sanfilippo <l.sanfilippo@...bus.com>,
 Serge Semin <fancer.lancer@...il.com>, linux-rpi-kernel@...ts.infradead.org,
 linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH tty-next v3 4/6] serial: 8250: Specify console context for
 rs485_start/stop_tx

On 25. 10. 24, 12:57, John Ogness wrote:
> For RS485 mode, if SER_RS485_RX_DURING_TX is not available, the
> console write callback needs to enable/disable TX. It does this
> by calling the rs485_start/stop_tx() callbacks. However, these
> callbacks will disable/enable interrupts, which is a problem
> for console write, as it must be responsible for
> disabling/enabling interrupts.
> 
> Add an argument @in_con to the rs485_start/stop_tx() callbacks
> to specify if they are being called from console write. If so,
> the callbacks will not handle interrupt disabling/enabling.
> 
> For all call sites other than console write, there is no
> functional change.
> 
> Signed-off-by: John Ogness <john.ogness@...utronix.de>
...
> @@ -1562,12 +1566,20 @@ static inline void __start_tx(struct uart_port *port)
>    * stoppable by disabling the UART_IER_RDI interrupt.  (Some chips set the
>    * UART_LSR_DR bit even when UART_IER_RDI is disabled, foiling this approach.)
>    */
> -void serial8250_em485_start_tx(struct uart_8250_port *up)
> +void serial8250_em485_start_tx(struct uart_8250_port *up, bool in_con)
>   {
>   	unsigned char mcr = serial8250_in_MCR(up);
>   
> -	if (!(up->port.rs485.flags & SER_RS485_RX_DURING_TX))
> -		serial8250_stop_rx(&up->port);
> +	if (!(up->port.rs485.flags & SER_RS485_RX_DURING_TX)) {
> +		/*
> +		 * In console context, caller handles interrupt disabling. So
> +		 * only LSR_DR masking is needed.
> +		 */
> +		if (in_con)
> +			__serial8250_stop_rx_mask_dr(&up->port);
> +		else
> +			serial8250_stop_rx(&up->port);

Would it make sense to propagate in_con into serial8250_stop_rx() and do 
the logic there? That would effectively eliminate patch 2/6.

thanks,
-- 
js
suse labs