linux-kernel - Re: USB transfer_buffer allocations on 64bit systems

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Message-ID: <20100408110743.GP30807@buzzloop.caiaq.de>
Date:	Thu, 8 Apr 2010 13:07:43 +0200
From:	Daniel Mack <daniel@...aq.de>
To:	Oliver Neukum <oliver@...kum.org>
Cc:	Greg KH <greg@...ah.com>, Alan Stern <stern@...land.harvard.edu>,
	linux-kernel@...r.kernel.org, Pedro Ribeiro <pedrib@...il.com>,
	akpm@...ux-foundation.org, Greg KH <gregkh@...e.de>,
	alsa-devel@...a-project.org, linux-usb@...r.kernel.org
Subject: Re: USB transfer_buffer allocations on 64bit systems

On Thu, Apr 08, 2010 at 08:09:11AM +0200, Oliver Neukum wrote:
> Am Mittwoch, 7. April 2010 17:35:51 schrieb Daniel Mack:
> > > Alan, any objection to just using usb_buffer_alloc() for every driver?
> > > Or is that too much overhead?
> > 
> > FWIW, most drivers I've seen in the past hours use a wild mix of
> > kmalloc(), kzalloc(), kcalloc() and usb_buffer_alloc(). That should
> > really be unified.
> 
> kmalloc() & friends != usb_buffer_alloc(). They do different things.

I know. I just believe that many developers used usb_buffer_alloc() even
though they don't really need coherent DMA memory. The function's name
is misleading, and copy'n paste does the rest.

> It makes no sense to unify them. If you really need an ordinary
> buffer DMA will surely work on, this needs a third primitive.

I think it will help a lot to rename usb_buffer_alloc() in the first
place and then reconsider where coherent memory is really needed.

Daniel
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