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From: Haavard Skinnemoen <hskinnemoen@atmel.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux@maxim.org.za, linux@bohmer.net, coldwell@redhat.com,
	marc.pignat@hevs.ch, david-b@pacbell.net,
	linux-kernel@vger.kernel.org, alan@lxorguk.ukuu.org.uk
Subject: Re: [PATCH -mm v4 7/9] atmel_serial: Add DMA support
Date: Mon, 28 Jan 2008 12:41:25 +0100	[thread overview]
Message-ID: <20080128124125.5c4e0a31@dhcp-252-066.norway.atmel.com> (raw)
In-Reply-To: <20080128022000.82ac86ab.akpm@linux-foundation.org>

On Mon, 28 Jan 2008 02:20:00 -0800
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Mon, 28 Jan 2008 10:59:09 +0100 Haavard Skinnemoen <hskinnemoen@atmel.com> wrote:
> 
> > > ho-hum.  The generic uart buffer-handling code does ringbuffers the wrong
> > > way.  Maybe it has to handle non-power-of-two buffer sizes.
> > 
> > Hmm...I don't understand. What does it do wrong?
> 
> An faq ;) If the buffer size is a power-of-two it's better to allow the
> head and tail indices wrap through 0xffffffff and only mask them when
> subscripting.  It ends up faster (usually) and you can use all of the
> elements of the buffer (rather than all-1) and you get nice things like:
> 
> is_empty = (head == tail)
> is_full = (tail - head == size)
> nr_items_in_ring = (tail - head)

Ok, that makes sense. Thanks for explaining. Not sure if want to start
improving things right now, although I'm pretty sure the circ stuff
can't handle non-power-of-two buffer size currently so it should be
possible.

> > > All those uart_circ_*() macros reference their arg more than once and ... 
> > > you know the deal.
> > 
> > Yeah. Would you like a patch that inline-ifies <linux/circ.h>?
> 
> uh, if you're feeling especially keen.  We have bigger problems than this.

Well, if you put it like that; no, not really.

I'll post a fix for the other things you pointed out shortly.

Haavard

  reply	other threads:[~2008-01-28 11:41 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-01-24 12:41 [PATCH -mm v4 0/9] atmel_serial cleanups and improvements Haavard Skinnemoen
2008-01-24 12:41 ` [PATCH -mm v4 1/9] MAINTAINERS: Add myself as maintainer of the atmel_serial driver Haavard Skinnemoen
2008-01-24 12:41   ` [PATCH -mm v4 2/9] atmel_serial: Clean up the code Haavard Skinnemoen
2008-01-24 12:41     ` [PATCH -mm v4 3/9] atmel_serial: Use cpu_relax() when busy-waiting Haavard Skinnemoen
2008-01-24 12:41       ` [PATCH -mm v4 4/9] atmel_serial: Use existing console options only if BRG is running Haavard Skinnemoen
2008-01-24 12:41         ` [PATCH -mm v4 5/9] atmel_serial: Fix bugs in probe() error path and remove() Haavard Skinnemoen
2008-01-24 12:41           ` [PATCH -mm v4 6/9] atmel_serial: Split the interrupt handler Haavard Skinnemoen
2008-01-24 12:41             ` [PATCH -mm v4 7/9] atmel_serial: Add DMA support Haavard Skinnemoen
2008-01-24 12:41               ` [PATCH -mm v4 8/9] atmel_serial: Use container_of instead of direct cast Haavard Skinnemoen
2008-01-24 12:41                 ` [PATCH -mm v4 9/9] atmel_serial: Show tty name in /proc/interrupts Haavard Skinnemoen
2008-01-27  6:02               ` [PATCH -mm v4 7/9] atmel_serial: Add DMA support Andrew Morton
2008-01-28  9:59                 ` Haavard Skinnemoen
2008-01-28 10:20                   ` Andrew Morton
2008-01-28 11:41                     ` Haavard Skinnemoen [this message]
2008-01-28 11:48                       ` [PATCH -mm] atmel_serial dma: Misc fixes and cleanups Haavard Skinnemoen
2008-01-24 13:32 ` [PATCH -mm v4 0/9] atmel_serial cleanups and improvements Marc Pignat
2008-01-24 15:07   ` Haavard Skinnemoen

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