linux-kernel - Re: [PATCH 3/6] serial: 8250_dw: Rework dw8250_handle

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Message-ID: <aXjCPu9BglNWec_F@smile.fi.intel.com>
Date: Tue, 27 Jan 2026 15:48:46 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>,
	linux-serial <linux-serial@...r.kernel.org>,
	qianfan Zhao <qianfanguijin@....com>,
	Adriana Nicolae <adriana@...sta.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Bandal, Shankar" <shankar.bandal@...el.com>,
	"Murthy, Shanth" <shanth.murthy@...el.com>
Subject: Re: [PATCH 3/6] serial: 8250_dw: Rework dw8250_handle_irq() locking
 and IIR handling

On Tue, Jan 27, 2026 at 02:48:30PM +0200, Ilpo Järvinen wrote:
> On Sat, 24 Jan 2026, Andy Shevchenko wrote:
> > On Fri, Jan 23, 2026 at 07:27:36PM +0200, Ilpo Järvinen wrote:

...

> > > dw8250_handle_irq() takes port's lock multiple times with no good
> > > reason to release it in between and calls serial8250_handle_irq()
> > > that also takes port's lock.
> > > 
> > > As serial8250_handle_irq() takes port's lock itself, create
> > > serial8250_handle_irq_locked() that allows caller to hold port's lock
> > > across the call. Take port's lock only once in dw8250_handle_irq() and
> > > call serial8250_handle_irq_locked() directly.
> > 
> > Sounds to me that the latter can be split to a prerequisite patch.
> 
> It's not easy to split this DW-side IIR rework and locking changes. What I 
> can do is to make 8250_port change separately. I guess I'll do just that 
> and only the 8250_dw change in this patch.

Yes, that's what I had in mind.

...

> > > +++ b/drivers/tty/serial/8250/8250_port.c
> > 
> > >  #include <linux/ioport.h>
> > >  #include <linux/init.h>
> > >  #include <linux/irq.h>
> > 
> > > +#include <linux/lockdep.h>
> > 
> > I would still keep more order.
> > 
> > >  #include <linux/console.h>
> > >  #include <linux/gpio/consumer.h>
> > 
> > Giving the context we have, the better place for a new inclusion is somewhere
> > here.
> 
> Feels to me something that is in the eye of the beholder, but whatever, I 
> can move it from one's "correct" place to somebody elses "correct"
> place. :-)

The idea is to have the longest ordered chain even if it's broken by some
unordered pieces. In long-term it helps to cleanup without an additional
churn.

> > >  #include <linux/sysrq.h>
> > 
> > (Also perhaps sorting headers in a separate patch helps with finding better
> >  places for the future inclusions?)
> 
> Yes, later (not in this series).

Sure!

...

> > > +EXPORT_SYMBOL_GPL(serial8250_handle_irq_locked);
> > 
> > Wondering if we can start exporting with a namespace...
> 
> I'll do that. I picked "SERIAL_8250", is that fine or should I use e.g.
> "8250" instead?

Since it's a string now, I have no preferences, but SERIAL_8250 sounds like
slightly better choice as it has not only digits (its own namespace in the
naming) and less chances to collide in the future.

-- 
With Best Regards,
Andy Shevchenko