Re: [PATCH for-4.22] char/ns16550: bound execution time of ns16550_interrupt()

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

On 6/23/26 12:31 PM, Roger Pau Monne wrote:
> The current logic in ns16550_interrupt() will loop until the device sets
> the NOINT in IIR.  At least on the Lenovo ThinkSystem SR630 V4 the flow
> control of the serial-over-lan emulated UART seems to be broken, as it
> doesn't set the NOINT bit consistently.  The Transmitter Holding Register
> Empty in LSR also seems to not be properly signaled, as even with it set
> writes to the transmit register take ~6ms.  This leads to the watchdog
> triggering very easily on such system.
>
> Introduce an upper bound on the execution time of ns16550_interrupt(), this
> is currently set as 4x the polling interval, which is calculated as the
> time to fill RX FIFO and/or empty TX FIFO.  The current maximum is 5ms.
> Once the timeout triggers the interrupt is disabled and the uart is
> switched to polling mode.
Don't you mmiss Fixes: tag?

> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>> ---
> There's a possible alternative approach to solve this by moving the actual
> interrupt processing to a softirq tasklet and disabling the interrupt
> source until the processing is done, likely unifying the logic with the
> timer task.  However that's a bigger change, and too risky for 4.22 at this
> point.
> ---
Agree, it would be better to stick to  the current solution:

Release-Acked-by: Oleksii Kurochko <oleskii.kurochko@xxxxxxxxx>

Thanks.

~ Oleksii