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

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Message-ID: <3424939f-3abc-4154-9cda-51abd657e889@vaisala.com>
Date: Thu, 4 Sep 2025 10:23:23 +0300
From: Tapio Reijonen <tapio.reijonen@...sala.com>
To: Hugo Villeneuve <hugo@...ovil.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Jiri Slaby <jirislaby@...nel.org>, Alexander Shiyan <shc_work@...l.ru>,
 Hugo Villeneuve <hvilleneuve@...onoff.com>, linux-kernel@...r.kernel.org,
 linux-serial@...r.kernel.org
Subject: Re: [PATCH] serial: max310x: improve interrupt handling

Hi,

On 9/3/25 18:37, Hugo Villeneuve wrote:
> Hi,
> 
> On Wed, 03 Sep 2025 09:23:04 +0000
> Tapio Reijonen <tapio.reijonen@...sala.com> 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.
> 
> To improve clarity and reduce confusion, maybe change to
> something like:
> 
> ... always service first the highest UART until
> no more interrupt and then service another UART (ex: UART3 will be
> serviced for as long as there are interrupts for it, then UART2, etc).
> 
> 
>>
>> This commit improve interrupt service routine to handle all
>> interrupt sources, e.g. UARTs when a global IRQ is detected.
> 
> The current code already handle all interrupt sources. What you
> maybe could be saying is that you handle all individual interrupt
> sources before reading the global IRQ register again?
> 
> You could also add in your commit message that your modification has the
> nice side-effect of improving the efficiency of the driver by reducing
> the number of reads of the global IRQ register.
> 
> 
Try to improve commit message in next patch version.

>>
>> 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));
> 
> You changed the indentation here...
> 
I'll fix the indentation, my fault.

>> +
>> +                     val = ((1 << s->devtype->nr) - 1) & ~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);
>>                } while (1);
>>        } else {
>>                if (max310x_port_irq(s, 0) == IRQ_HANDLED)
> 
> Maybe you could simplify (and improve readability) with this instead:
> 
I am reviewing the proposal.

> ---
>                          val = ((1 << s->devtype->nr) - 1) & ~val;
>                          if (!val)
>                                  break;
> 
> -                       if (max310x_port_irq(s, fls(val) - 1) == IRQ_HANDLED)
> -                               handled = true;
> +
> +                       do {
> +                               unsigned int channel;
> +
> +                               channel = fls(val) - 1;
> +
> +                               if (max310x_port_irq(s, channel) == IRQ_HANDLED)
> +                                       handled = true;
> +
> +                               val &= ~(1 << channel);
> +                       } while (val);
> ---
> 
>>
>> ---
>> base-commit: c8bc81a52d5a2ac2e4b257ae123677cf94112755
>> change-id: 20250903-master-max310x-improve-interrupt-handling-aa22b7ba1c1d
>>
>> Best regards,
>> --
>> Tapio Reijonen <tapio.reijonen@...sala.com>
>>
>>
>>
> 
> --
> Hugo Villeneuve

--
Many thanks,
Tapio Reijonen