Regression: serial: imx: overrun errors on debug UART

[Thorsten Leemhuis]

On 23.05.23 21:44, Sergey Organov wrote:
> "Linux regression tracking (Thorsten Leemhuis)"
> <regressions at leemhuis.info> writes:
> 
>> Hi, Thorsten here, the Linux kernel's regression tracker. Top-posting
>> for once, to make this easily accessible to everyone.
>>
>> Stefan, was this regression ever solved? It doesn't look like it, but
>> maybe I'm missing something.
>>
>> If it wasn't solved: what needs to be done to get this rolling again?
> 
> Not Stefan,

Thx to both you and Stefan for the update.

> but as far as I can tell, the problem is that on Stefan's
> build the kernel has rather large periods of interrupts being disabled,
> so any attempt to decrease IRQs frequency from UART by raising FIFO IRQ
> threshold causes "regression" that manifests itself as missing
> characters on receive. I'm not sure if it's tuning FIFO level that is in
> fact a regression in this case.

Not totally sure, but I guess Linus stance in this case would be along
the lines of "commit 7a637784d517 made an existing issue worse; either
the people involved in it fix it, or we revert that commit[1], as it's
causing a regression". At least we *iirc* had situations he handled like
that.

[1] of course unless a revert would cause regressions for others --
which i guess might be the case here, as that was added in 5.18 already.
So let's not bring Linus in.

> Solving this would need to identify the cause of interrupts being
> disabled for prolonged times, and nobody volunteered to investigate this
> further. 

Well, Stefan kind of did to do so in his spare time, but asked for
"clear instructions to investigate this further". Could you maybe
provide those? If not: who could?

> One suspect, the Linux serial console, has been likely excluded
> already though, as not actually being in use for printk() output.

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
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