Messages in this thread | | | Date | Mon, 28 Jan 2008 12:41:25 +0100 | From | Haavard Skinnemoen <> | Subject | Re: [PATCH -mm v4 7/9] atmel_serial: Add DMA support |
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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
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