From: Oliver Neukum <oliver@neukum.org>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: USB mass storage and ARM cache coherency
Date: Wed, 17 Feb 2010 11:09:31 +0100
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Cc: "Shilimkar, Santosh" <santosh.shilimkar@ti.com>,
       Matthew Dharm <mdharm-kernel@one-eyed-alien.net>,
       "Russell King - ARM Linux" <linux@arm.linux.org.uk>,
       Ming Lei <tom.leiming@gmail.com>,
       "Mankad, Maulik Ojas" <x0082077@ti.com>,
       Sergei Shtylyov <sshtylyov@ru.mvista.com>,
       Catalin Marinas <catalin.marinas@arm.com>,
       Sebastian Siewior <bigeasy@linutronix.de>,
       "linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
       "linux-kernel" <linux-kernel@vger.kernel.org>,
       Pavel Machek <pavel@ucw.cz>, Greg KH <greg@kroah.com>,
       "linux-arm-kernel" <linux-arm-kernel@lists.infradead.org>
References: <20100208065519.GE1290@ucw.cz> <201002171015.52875.oliver@neukum.org> <1266399609.16346.271.camel@pasglop>
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Am Mittwoch, 17. Februar 2010 10:40:09 schrieb Benjamin Herrenschmidt:
> What bugs me here is that the dma_map_* operation should always
> be done at the lowest level, ie, the actual HCD driver, and thus
> it should be up to the HCD to decide whether to dma_map or not
> depending on whether it's going to do DMA or not. I haven't
> scrutinized USB lately but if that isn't the case and the dma_map_*
> operations are done behind your back by the USB core then that needs to
> be changed in a way or another, or hooked at least.

No problem here. USB core does the mapping only if the low-level driver
so requests. The only exception is in usb_buffer_alloc(), but that boils
down to dma_alloc_coherent()

	Regards
		Oliver
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