Re: [PATCH 0/6] tty: serial: propagate errors from uart_ops.pm callback

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Thu, Jul 09, 2026 at 11:55:12AM +0530, Praveen Talari wrote:
> The uart_ops.pm callback has been declared void since its introduction,
> which means any error from a driver's power management implementation is
> silently discarded by uart_change_pm(). Beyond losing the error
> information, uart_change_pm() unconditionally updates state->pm_state
> even when the underlying hardware transition failed. This causes the
> serial core to track a power state that does not reflect reality:
> subsequent calls to uart_change_pm() see the stale cached state as
> matching the requested state and skip the callback entirely, leaving the
> hardware permanently stuck with no further recovery attempt.
> 
> On modern platforms where the .pm callback performs real work —
> enabling clock trees, interacting with runtime PM, asserting voltage
> regulators — this is a correctness gap. Failures are invisible to the
> PM framework, the port proceeds to call ops->startup() on potentially
> unpowered hardware, and suspend/resume errors are hidden from the core
> that needs to handle them.
> 
> This series fixes the problem in four steps:
> 
>   Patch 1 changes the uart_ops.pm callback signature from void to int,
>   updates uart_change_pm() to propagate errors and only commit
>   state->pm_state on success, and handles the return value at every
>   call site in serial_core.c with appropriate policy per context
>   (propagate, log, or skip-on-failure).
> 
>   Patch 2 updates the 8250 driver family: serial8250_do_pm() and
>   serial8250_pm() are updated to return int (with the exported symbol
>   declaration updated in serial_8250.h), and the 8250 sub-driver
>   pm callbacks are updated to return 0.
> 
>   Patch 3 updates the remaining non-8250 serial drivers. All .pm
>   implementations are updated to return 0. The sh-sci forward
>   declaration shared with rsci is also updated.
> 
>   Patch 4 updates arch-level implementations: SA1100 (assabet, h3xxx),
>   OMAP1/ams-delta (modem_pm, now propagates regulator errors), and
>   MIPS/Alchemy (alchemy_8250_pm).
> 
> All existing .pm implementations return 0, so there is no functional
> change for any current driver. The series purely adds the infrastructure
> for drivers to report errors going forward, with the serial core ready
> to handle them correctly.

Just no, please just properly implement runtime PM. The .pm() must die completely.
I used to have the PoC for that long time ago [1], but due to lack of time and
other priorities it went abandoned. Also Atlassian made a brain damages move to
limit repository to 1Gb, so I haven't able to update it for a few years.

Note, that Tony (you have him in the Cc list) did a lot for some corner cases
with that and we still have them IIRC. Tony, do you know what is the state of
affairs with runtime PM for UART?

[1]: https://bitbucket.org/andy-shev/linux/branch/topic/uart/rpm-plus

-- 
With Best Regards,
Andy Shevchenko