linux-kernel - Re: USB mass storage and ARM cache coherency

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Message-Id: <201002171109.32107.oliver@neukum.org>
Date:	Wed, 17 Feb 2010 11:09:31 +0100
From:	Oliver Neukum <oliver@...kum.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	"Shilimkar, Santosh" <santosh.shilimkar@...com>,
	Matthew Dharm <mdharm-kernel@...-eyed-alien.net>,
	"Russell King - ARM Linux" <linux@....linux.org.uk>,
	Ming Lei <tom.leiming@...il.com>,
	"Mankad, Maulik Ojas" <x0082077@...com>,
	Sergei Shtylyov <sshtylyov@...mvista.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Sebastian Siewior <bigeasy@...utronix.de>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel" <linux-kernel@...r.kernel.org>,
	Pavel Machek <pavel@....cz>, Greg KH <greg@...ah.com>,
	"linux-arm-kernel" <linux-arm-kernel@...ts.infradead.org>
Subject: Re: USB mass storage and ARM cache coherency

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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