linux-kernel - Re: usb_get_status(): what a weird implementation !

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Message-Id: <200806301551.42252.oliver@neukum.org>
Date:	Mon, 30 Jun 2008 15:51:41 +0200
From:	Oliver Neukum <oliver@...kum.org>
To:	"Francis Moreau" <francis.moro@...il.com>
Cc:	"David Brownell" <david-b@...bell.net>, linux-usb@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: usb_get_status(): what a weird implementation !

Am Montag 30 Juni 2008 14:41:37 schrieb Francis Moreau:
> On Mon, Jun 30, 2008 at 1:46 PM, Oliver Neukum <oliver@...kum.org> wrote:
> > Am Montag 30 Juni 2008 13:04:21 schrieb Francis Moreau:

> >> well, it wouldn't be hard to allocated a buf on the stack with correct
> >> alignement
> >> and size for DMA mapping.
> >
> > Where would you put it and meet the alignment requirements?
> >
> 
> wouldn't this code below do the trick ?
> 
> void foo(void)
> {
>     unsigned char __buf[2 * CACHE_LINE_SIZE];
>     unsigned char *buf;
> 
>     buf = ((unsigned long)__buf) + CACHE_LINE_SIZE-1) & ~(CACHE_LINE_SIZE-1);
> }
> 
> but I agree it looks hackish.

If your buffer is smaller than CACHE_LINE_SIZE it should work.
However, this needs input from people who understand DMA in and out.
But how large is 2 * CACHE_LINE_SIZE compared to the kernel stack?

	Regards
		Oliver
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