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

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Message-ID: <20100217202617.GB30033@n2100.arm.linux.org.uk>
Date:	Wed, 17 Feb 2010 20:26:17 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"Shilimkar, Santosh" <santosh.shilimkar@...com>,
	Oliver Neukum <oliver@...kum.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Pavel Machek <pavel@....cz>, Greg KH <greg@...ah.com>,
	Matthew Dharm <mdharm-kernel@...-eyed-alien.net>,
	Sergei Shtylyov <sshtylyov@...mvista.com>,
	Ming Lei <tom.leiming@...il.com>,
	Sebastian Siewior <bigeasy@...utronix.de>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	"Mankad, Maulik Ojas" <x0082077@...com>,
	"Gadiyar, Anand" <gadiyar@...com>
Subject: Re: USB mass storage and ARM cache coherency

On Wed, Feb 17, 2010 at 12:02:21PM -0500, Alan Stern wrote:
> Why do you skip mapping the setup packet but not the data packet?

This is something of a FAQ in this thread.  Here are the responses to
similar questions yesterday:

"Gadiyar, Anand" <gadiyar@...com> said:
> Not really. For instance, in the case of the DMA engine in the MUSB
> controller in OMAP3, we can only use DMA with endpoints other than
> EP0, and EP0 is what is used for control transfers.
>
> It's not PIO for all the endpoints or DMA for all of them.

"Shilimkar, Santosh" <santosh.shilimkar@...com> said:
> On the OMAP4 (ARM cortex-a9) platform, the enumeration fails because control
> transfer buffers are corrupted. On our platform, we use PIO mode for control
> transfers and DMA for bulk transfers.
>
> The current stack performs dma cache maintenance even for the PIO transfers
> which leads to the corruption issue. The control buffers are handled by CPU
> and they already coherent from CPU point of view.

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