linux-kernel - Re: [PATCH] serial: max310x: improve interrupt handling

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Message-ID: <214edb7a-2631-4f7f-9516-a38a3796cc0b@kernel.org>
Date: Thu, 4 Sep 2025 09:53:25 +0200
From: Jiri Slaby <jirislaby@...nel.org>
To: Tapio Reijonen <tapio.reijonen@...sala.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Alexander Shiyan <shc_work@...l.ru>,
 Hugo Villeneuve <hvilleneuve@...onoff.com>
Cc: linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH] serial: max310x: improve interrupt handling

On 03. 09. 25, 11:23, Tapio Reijonen wrote:
> When there is a heavy load of receiving characters to all
> four UART's, the warning 'Hardware RX FIFO overrun' is
> sometimes detected.
> The current implementation always service first UART3 until
> no more interrupt and then service another UARTs.
> 
> This commit improve interrupt service routine to handle all
> interrupt sources, e.g. UARTs when a global IRQ is detected.
> 
> Signed-off-by: Tapio Reijonen <tapio.reijonen@...sala.com>
> ---
>   drivers/tty/serial/max310x.c | 21 ++++++++++++++++-----
>   1 file changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/tty/serial/max310x.c b/drivers/tty/serial/max310x.c
> index ce260e9949c3c268e706b2615d6fc01adc21e49b..3234ed7c688ff423d25a007ed8b938b249ae0b82 100644
> --- a/drivers/tty/serial/max310x.c
> +++ b/drivers/tty/serial/max310x.c
> @@ -824,15 +824,26 @@ static irqreturn_t max310x_ist(int irq, void *dev_id)
>   
>   	if (s->devtype->nr > 1) {
>   		do {
> -			unsigned int val = ~0;
> +			unsigned int val;
> +			unsigned int global_irq = ~0;
> +			int port;
>   
>   			WARN_ON_ONCE(regmap_read(s->regmap,
> -						 MAX310X_GLOBALIRQ_REG, &val));
> -			val = ((1 << s->devtype->nr) - 1) & ~val;
> +				MAX310X_GLOBALIRQ_REG, &global_irq));
> +
> +			val = ((1 << s->devtype->nr) - 1) & ~global_irq;

This is horrid. Use GENMASK() (or BIT() below) instead. Likely, you want 
a local var storing the mask (the first part before the &).

>   			if (!val)
>   				break;
> -			if (max310x_port_irq(s, fls(val) - 1) == IRQ_HANDLED)
> -				handled = true;
> +
> +			do {
> +				port = fls(val) - 1;
> +				if (max310x_port_irq(s, port) == IRQ_HANDLED)
> +					handled = true;
> +
> +				global_irq |= 1 << port;
> +				val = ((1 << s->devtype->nr) - 1) & ~global_irq;
> +			} while (val);

Actually, does it have to be from the end? I am thinking of 
for_each_and_bit()...

>   		} while (1);
>   	} else {
>   		if (max310x_port_irq(s, 0) == IRQ_HANDLED)

thanks,
-- 
js
suse labs