Date: Mon, 12 Apr 2010 13:53:00 +0200
From: Andi Kleen <andi@firstfloor.org>
To: Daniel Mack <daniel@caiaq.de>
Cc: Andi Kleen <andi@firstfloor.org>, Alan Stern <stern@rowland.harvard.edu>,
       linux-kernel@vger.kernel.org, Pedro Ribeiro <pedrib@gmail.com>,
       akpm@linux-foundation.org, Greg KH <gregkh@suse.de>,
       alsa-devel@alsa-project.org, linux-usb@vger.kernel.org
Subject: Re: USB transfer_buffer allocations on 64bit systems
Message-ID: <20100412115300.GM18855@one.firstfloor.org>
References: <20100407090623.GN30807@buzzloop.caiaq.de> <Pine.LNX.4.44L0.1004071036060.1779-100000@iolanthe.rowland.org> <87sk719hbm.fsf@basil.nowhere.org> <20100412111439.GU30801@buzzloop.caiaq.de>
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> Which is exactly what usb_buffer_alloc() does already. So at least for
> x86 you say this is the right thing to do? However, we don't necessarily
> need coherent memory on other platforms, which is why I hessitate to
> enforce that type of memory for all transfer_buffer allocations.

Yes today it's faster at least.

Probably we should have better interfaces for this, but we don't.

> 
> > Or just use GFP_KERNEL and pci_map_* later.
> 
> The USB core does this already, but at least on Pedro's machine, this
> seems unsufficient. Unfortunately, I can't reproduce the issue yet, even
> with more than 4GB of RAM installed.

Then something must be broken in Pedro's system and likely other drivers
will also not work. I don't think it should be worked around in the USB layer.

-Andi
-- 
ak@linux.intel.com -- Speaking for myself only.
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