On 04/11/2024 15:15, Petr Mladek wrote:
On Mon 2024-11-04 11:52:33, John Ogness wrote:
On 2024-11-04, Jocelyn Falempe <jfalempe@xxxxxxxxxx> wrote:
I looked at what serial drivers are doing, because they can also have
their clock gated in suspend.
Would calling console_stop() in the suspend and console_start() in
resume work ?
Yes. That is what it is for.
It seems that you are right. I have never really investigated the purpose
of this API /o\
Thanks, I will send a v6 with that change.
One problem with this API is that it does not check whether the
console is registered. I wonder whether it might cause problems.
At least for drm_log, register_console() will always be called before.
For example, we should not set the CON_ENABLE flag when the console is not
registered. Doing so would cause register_console() to always enable
the console, even when it is not preferred.
Additionally, nbcon_kthread_wake() uses con->rcuwait, which is initialized
by nbcon_alloc() called from register_console(). Fortunately, nbcon_alloc()
is always called even if the console is not enabled in the end, but this
might change in the future and cause subtle errors.
[ After even more thinking ]
I wonder whether console_start()/console_stop() should really
manipulate CON_ENABLE flag. It might be historical solution when
@console_suspended was a global variable.
But it has changed with the commit 9e70a5e109a4a2336 ("printk: Add
per-console suspended state").
It might make more sense when console_start()/console_stop()
manipulates CON_SUSPENDED flag. Then it would make sense
to rename them suspend_this_console()/resume_this_console().
What do you think?
Maybe when registering the console, having a flag to say "I want this
console to be suspended with the console subsystem" or "I want to handle
suspend/resume on my own, and call the relevant functions" would be better ?
That would avoid having the same console being suspended/resumed twice,
and making clear what to expect.
Of course "no_console_suspend" won't really work for drivers handling
suspend/resume themselves.
--
Jocelyn
Best Regards,
Petr
