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

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Date:	Tue, 2 Feb 2010 15:39:05 +0900
From:	Paul Mundt <lethal@...ux-sh.org>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Matthew Dharm <mdharm-kernel@...-eyed-alien.net>,
	Sergei Shtylyov <sshtylyov@...mvista.com>,
	Ming Lei <tom.leiming@...il.com>, linux-usb@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Sebastian Siewior <bigeasy@...utronix.de>,
	Greg KH <greg@...ah.com>
Subject: Re: USB mass storage and ARM cache coherency

On Mon, Feb 01, 2010 at 05:29:14PM +0000, Catalin Marinas wrote:
> On Fri, 2010-01-29 at 18:54 +0000, Matthew Dharm wrote:
> > HOWEVER, I firmly believe that the cache-management functions belong with
> > the driver that actually talks to the low-level hardware, as that's the
> > only place where you can be 100% certain of what cache operations are
> > needed.  After all, I think someone is working on a USB-over-IP transport,
> > and trying to manage cache at the usb-storage level in that scenario is
> > just silly.
> > 
> > So, let's put this in the HCD drivers and be done with it.
> 
> The patch below is what fixes the I-D cache incoherency issues on ARM. I
> don't particularly like the solution but it seems to be the only one
> available.
> 
> IMHO, Linux should have functions similar to the DMA API but for PIO
> drivers (e.g. pio_map_single/pio_unmap_single) that non-coherent
> architectures can define, otherwise being no-ops. Any thoughts?
> 
I would certainly be in favour of such a thing, particularly since on SH
we often find ourselves with coherent PIO and non-coherent MMIO.

This is however something that should be prototyped and submitted to
linux-arch for discussion.

> diff --git a/drivers/usb/host/isp1760-hcd.c b/drivers/usb/host/isp1760-hcd.c
> index 27b8f7c..4d3eeee 100644
> --- a/drivers/usb/host/isp1760-hcd.c
> +++ b/drivers/usb/host/isp1760-hcd.c
> @@ -18,6 +18,8 @@
>  #include <linux/uaccess.h>
>  #include <linux/io.h>
>  #include <asm/unaligned.h>
> +#include <asm/cacheflush.h>
> +#include <asm/memory.h>
>  
asm/memory.h isn't a portable header. If you are including it for
virt_to_page(), linux/io.h should already bring that in via asm/io.h.
If arm doesn't bring in virt_to_page() through its asm/io.h, then fix the
headers there please.

FWIW I used the same fix you came up with on r8a66597_hcd and it fixed up
crashes we were seeing there, too.
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