linux-kernel - Re: [PATCH 6/6] atmel

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Message-Id: <200801231330.32777.marc.pignat@hevs.ch>
Date:	Wed, 23 Jan 2008 13:30:32 +0100
From:	Marc Pignat <marc.pignat@...s.ch>
To:	Haavard Skinnemoen <hskinnemoen@...el.com>
Cc:	Andrew Victor <linux@...im.org.za>, kernel@...32linux.org,
	linux-kernel@...r.kernel.org, Remy Bohmer <linux@...mer.net>,
	Chip Coldwell <coldwell@...hat.com>
Subject: Re: [PATCH 6/6] atmel_serial: Add DMA support

Hi!

On Wednesday 23 January 2008, Haavard Skinnemoen wrote:
> On Tue, 22 Jan 2008 17:52:43 +0100
> Marc Pignat <marc.pignat@...s.ch> wrote:
> 
> > Hi!
> > 
> > I removed linux-arm-kernel@...ts.arm.linux.org.uk from cc, it is a
> > subscriber-only list.
> 
> Right. Does that mean I shouldn't Cc it on patches?
extract from the linux-arm-kernel 'Mailing List Etiquette':
             10. Cross-posting between linux-arm* lists and other lists. [[40]rmk]
                Please do not do this. Subscribers on other lists may not be
                subscribed to the linux-arm lists, so when they try to reply to
                such a message, they will receive a bounce. This is deemed by
                others to be rude behaviour on the part of the person who
                originally cross-posted.
> 
> > On Tuesday 22 January 2008, Haavard Skinnemoen wrote:
> > > From: Chip Coldwell <coldwell@...hat.com>
> > ...
> > > @@ -47,6 +50,11 @@
> > >  
> > >  #include "atmel_serial.h"
> > >  
> > > +#define SUPPORT_PDC
> > > +#define PDC_BUFFER_SIZE		(L1_CACHE_BYTES << 3)
> > > +#warning "Revisit"
> > why add this warning?
> 
> Dunno. I suppose the PDC_BUFFER_SIZE and/or PDC_RX_TIMEOUT definitions
> needs to be revisited? Chip?
I just think there is no need to warn, even if definitions are sub-optimal.

> 
> I don't really understand why the buffer size depends on the cache line
> size either. Why don't we just set it to something nice and large, like
> 512 (actually 1024 since there are two buffers), and be done with it?
Probably for dma safety/performance, The PDC buffer start should be aligned to
cache line, and the size be a multiple of cache line size.

> 
> And while we're at it, might as well move the SUPPORT_PDC definition
> into Kconfig where it belongs...
For me there is no need to disbable pdc support once working. PDC can be
enabled/disabled in the board setup code. -> simply remove this definition.

Regards

Marc

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