Subject: Re: USB CF reader problems with 2.0beta
To: Manuel Bouyer <bouyer@antioche.eu.org>
From: Lennart Augustsson <lennart@augustsson.net>
List: port-i386
Date: 05/02/2004 12:49:52
Manuel Bouyer wrote:
> On Sun, May 02, 2004 at 07:19:11PM +0300, Jukka Marin wrote:
> 
>>On Sun, May 02, 2004 at 06:11:15PM +0200, Manuel Bouyer wrote:
>>
>>>It needs N contigous pages. In theory you can have Ram/N allocated and
>>>have it still fail, if the memory fragmentation is at its maximum.
>>>I think this can be worked around by bumping a kernel parameter,
>>>but I don't remember which one :(
>>
>>Why does it need such a big buffer?  For maximum performance, sure, but..
>>(Well, I guess using anything more than one page would potentially cause
>>the same problem..)
> 
> 
> I think it's a hardware issue: the USB controller reading only contigous
> pages, or something like it.
> Based on this , the buffer size may be 64k, or 64k + 1 page. But it's only
> a guess, I didn't look at the code.

Yes, it's a 64K buffer.  The controller can deal with non-contigous
pages and it's just laziness on my part that it doesn't.
BUT, it used to work just fine allocating 64K.  I don't understand
how memory can get so fragmented.

	-- Lennart