Re: [REQUEST] Backport 8250_dw BUSY deassert series to 6.12.y stable

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

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On Fri, 8 May 2026, Ionut Nechita (Wind River) wrote:

> From: Ionut Nechita <ionut.nechita@windriver.com>
> 
> Hi Greg,
> 
> Fair question. We're shipping 6.12 as part of a certified platform
> (StarlingX/Yocto) that is already deployed in production at customer
> sites. A major kernel version bump requires a full re-qualification
> cycle across the entire platform stack (RT latency validation,
> out-of-tree driver compat, storage/networking regression testing),
> which is a multi-month effort we cannot justify for a single
> subsystem fix.
> 
> We are planning the move to a newer LTS for our next major release,
> but for the current production branch 6.12 is what we're committed to.
> 
> Since patch 7/7 already carries Cc: stable, would it be possible to
> pull in just the minimal dependencies needed to make it apply on
> 6.12.y? We're happy to do the backport work ourselves and submit it
> for review if that helps — we just wanted to check with Ilpo first
> on what the correct minimal subset would be before sending something
> that might be wrong.

Ah, this didn't get backported that far likely due to some syntax related 
changes causing conflicts with the series.

To backport the entire series my suggestion is to take parts of the 
commits:

dbd26a886e94 ("serial: 8250: use serial_port_in/out() helpers") (8250_dw.c only or just all if it goes cleanly)
b339809edda1 ("serial: 8250: use guard()s") (8250_port.c shutdown hunks)

And this completely (just syntax changes):

bd8cad85561b ("serial: 8250_dw: Comment possible corner cases in serial_out() implementation")

Those above are effectively just syntax changes but result in conflicts if 
not applied prior to the BUSY fix series.

This leaves only minor conflicts in:

a7b9ce39fbe4 ("serial: 8250_dw: Ensure BUSY is deasserted")
with type change in
fc9ceb501e38 ("serial: 8250: sanitize uart_port::serial_{in,out}() types")
(trivial resolution as the change was in the code removed by the BUSY 
change)

73a4ed8f9efa ("serial: 8250_dw: Rework IIR_NO_INT handling to stop interrupt storm")
with probe function changes (handle_irq assignment changes and unrelated 
dw8250_setup_dma_filter() change) in
c213375e3283 ("serial: 8250_dw: Call dw8250_quirks() conditionally")

Hope this helps.

-- 
 i.