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

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Message-ID: <20100407161603.GL30801@buzzloop.caiaq.de>
Date:	Wed, 7 Apr 2010 18:16:03 +0200
From:	Daniel Mack <daniel@...aq.de>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Greg KH <greg@...ah.com>, 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 Wed, Apr 07, 2010 at 11:55:19AM -0400, Alan Stern wrote:
> On Wed, 7 Apr 2010, Greg KH wrote:
> 
> > Alan, any objection to just using usb_buffer_alloc() for every driver?
> > Or is that too much overhead?
> 
> I don't know what the overhead is.  But usb_buffer_alloc() requires the 
> caller to keep track of the buffer's DMA address, so it's not a simple 
> plug-in replacement.  In addition, the consistent memory that 
> usb_buffer_alloc() provides is a scarce resource on some platforms.
> 
> Writing new functions is the way to go.

Ok, I'll write some dummies for usb_malloc() and usb_zalloc() which
will just call kmalloc() with GFP_DMA32 for now. And while at it,
usb_alloc_buffer() will be renamed to usb_alloc_consistent(). Then I'll
try to clean up all existing drivers to use this new interface and
follow the changes.

In a next step, we should fine-tune when GFP_DMA32 is really needed.
And I'll leave all occurances of usb_alloc_consistent() as they are now.

Does that sound ok?

Thanks,
Daniel

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