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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <e88f3c74-2ea0-4266-b5f7-62b87a1987c5@vaisala.com>
Date: Thu, 4 Sep 2025 14:50:16 +0300
From: Tapio Reijonen <tapio.reijonen@...sala.com>
To: Jiri Slaby <jirislaby@...nel.org>,
 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

Hi,

On 9/4/25 10:53, Jiri Slaby wrote:
> 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 &).
> 
val = GENMASK(s->devtype->nr - 1, 0) & ~global_irq;>>               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,

--
Many thanks,
Tapio Reijonen