linux-kernel - Re: [PATCH]: Atmel Serial Console interrupt handler splitup

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Message-ID: <20071217234932.GH23657@flint.arm.linux.org.uk>
Date:	Mon, 17 Dec 2007 23:49:32 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Remy Bohmer <linux@...mer.net>
Cc:	Haavard Skinnemoen <hskinnemoen@...el.com>,
	linux-kernel@...r.kernel.org,
	ARM Linux Mailing List 
	<linux-arm-kernel@...ts.arm.linux.org.uk>,
	Andrew Victor <linux@...im.org.za>,
	Steven Rostedt <rostedt@...dmis.org>,
	RT <linux-rt-users@...r.kernel.org>
Subject: Re: [PATCH]: Atmel Serial Console interrupt handler splitup

On Mon, Dec 17, 2007 at 09:56:30PM +0100, Remy Bohmer wrote:
> > > +#define lread(port)          __raw_readl(port)
> > > +#define lwrite(v, port)              __raw_writel(v, port)
> >
> > Why is this necessary, and what does 'l' stand for?
> 
> There is a huge list of macros below these definitions. By doing it
> this way, the macros still fit on 80 characters wide, while without
> them, I had split up the macros over several lines, which does not
> make it more readable. That's all.
> 'l' refers at the last letter of __raw_readl, and writel. Nothing special.

So why not keep to the Linux convention?  How about at_readl() and
at_writel() ?

> > >  /*
> > > + * receive interrupt handler.
> > > + */
> > > +static inline void
> > > +atmel_handle_receive(struct uart_port *port, unsigned int pending)
> >
> > Please drop "inline" here. The compiler will do it automatically if it
> > has only one caller, and if it at some point gets several callers, we
> > might not want to inline it after all.
> 
> Funny, This was the first thing that Andrew started complaining about.
> He suggested to put an inline there which I had not. I already
> mentioned that this was against the CodingStyle, but I also mentioned
> that I did not wanted to start a fight about this :-)
> So, to prevent a discussion, I added the inline...

There's two schools of thought - those who want to add 'inline' keywords
all over the place and those who don't.  It's quite correct that if a
static function will be inlined by the compiler as it sees fit.  It
_can_ be that the compiler will chose not to inline it and that may
result in better register allocation in the caller, resulting in overall
faster code.

> >
> > > +     while (!(UART_GET_CSR(port) & ATMEL_US_TXEMPTY))
> > > +             barrier();
> >
> > Should probably use cpu_relax(), but it's probably out of scope for a
> > codingstyle cleanup patch (and I don't think it matters on AVR32 or
> > ARM.)
> 
> Agree.

Even though it doesn't matter at the moment, I rather like to think a
bit about the future.  If the kernel has a simple and cheap mechanism
there's no reason to avoid using it.

> 
> > >       /*
> > > -      *      First, save IMR and then disable interrupts
> > > +      *      First, save IMR and then disable interrupts
> > >        */
> > >       imr = UART_GET_IMR(port);       /* get interrupt mask */
> > >       UART_PUT_IDR(port, ATMEL_US_RXRDY | ATMEL_US_TXRDY);
> > > @@ -790,30 +828,32 @@ static void atmel_console_write(struct c
> > >       uart_console_write(port, s, count, atmel_console_putchar);
> > >
> > >       /*
> > > -      *      Finally, wait for transmitter to become empty
> > > -      *      and restore IMR
> > > +      *      Finally, wait for transmitter to become empty
> > > +      *      and restore IMR
> > >        */
> >
> > Looks like you're replacing TABs with spaces. Why?
> 
> ????

I think someone's mailer might be messing with the patches.  The above
removed and added lines appear to be identical.
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