linux-kernel - Re: [PATCH v7] serial: support for 16550A serial ports on LP-8x4x

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Message-ID: <1456852472.23036.124.camel@gmail.com>
Date:	Tue, 01 Mar 2016 20:14:32 +0300
From:	Sergei Ianovich <ynvich@...il.com>
To:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Cc:	Alan Cox <gnomes@...rguk.ukuu.org.uk>,
	Arnd Bergmann <arnd@...db.de>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Masahiro Yamada <yamada.masahiro@...ionext.com>,
	Paul Burton <paul.burton@...tec.com>,
	Mans Rullgard <mans@...sr.com>,
	Joachim Eastwood <manabian@...il.com>,
	Scott Wood <scottwood@...escale.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Ujfalusi <peter.ujfalusi@...com>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
	<devicetree@...r.kernel.org>,
	"open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>
Subject: Re: [PATCH v7] serial: support for 16550A serial ports on LP-8x4x

On Tue, 2016-03-01 at 18:46 +0200, Andy Shevchenko wrote:
> On Tue, 2016-03-01 at 19:25 +0300, Sergei Ianovich wrote:
> > On Tue, 2016-03-01 at 13:06 +0200, Andy Shevchenko wrote:
> > > On Tue, 2016-03-01 at 00:26 +0300, Sergei Ianovich wrote:
> 
> > > > +	len &= 3;
> 
> Mask as well to be defined.

Sure.

> So, but if you support only fixed rates, why do you care about BOTHER
> at all?

If BOTHER is defined, tty_termios_baud_rate()
and tty_termios_encode_baud_rate() allow non-standard baud rates. I
should clear it from c_cflag to indicate I don't support it.

> > > >  
> > > I think you can call this unconditionally together with case >
> > > 115200.
> > 
> > The calls are orthogonal. This one deals with the case when BOTHER
> > is
> > defined and set, and we have non-zero rate with BOTHER, but we have
> > zero rate after BOTHER is cleared. So we set 9600 as a sane default
> > speed.

> > 
> > This one deals with the case when the rate is over 115200. If the
> > previous case has been triggered, this one won't be.
> 
> Yeah, but I meant to unconditionally call it just once here every
> time.

I see. It saves a few lines.

> > ---
> > drivers/tty/serial/8250/8250_lp8841.c: In function
> > 'lp8841_serial_probe':
> > drivers/tty/serial/8250/8250_lp8841.c:124:32: warning: excess
> > elements in struct initializer
> >   struct uart_8250_port uart = {0};
> >                                 ^
> > drivers/tty/serial/8250/8250_lp8841.c:124:32: note: (near
> > initialization for 'uart.port.lock.<anonymous>.rlock.raw_lock')
> 
> Do you have any warning verbosity enabled? I see a lot of stuff like
> this in the code

Plain `make`.

The warning seems to be the result of initializing a spinlock with
zero. Spinlocks are intentionally obfuscated, but I didn't investigate
further.

> $ git grep -n 'struct .* = {0};' | wc -l
> 338
> 
> $ git grep -n 'struct .* = { \?0 \?};' | wc -l
> 550
> 
> ( '… = { 0 };' included)

The first structure member is most likely not a spinlock in those
cases.

> > ---
> > 
> > Zero triggers a warning. I'll use memset().
> 
> Either will work.

OK

The only remaining open point is BOTHER handling.