From mboxrd@z Thu Jan  1 00:00:00 1970
From: zaitcev@redhat.com (Pete Zaitcev)
Date: Sat, 20 Feb 2010 00:21:48 -0700
Subject: USB mass storage and ARM cache coherency
In-Reply-To: <5A47E75E594F054BAF48C5E4FC4B92AB03215B07FF@dbde02.ent.ti.com>
References: <20100208065519.GE1290@ucw.cz>
	<1265622676.4020.19.camel@pc1117.cambridge.arm.com>
	<20100208105209.GA31671@atrey.karlin.mff.cuni.cz>
	<1265628483.4020.63.camel@pc1117.cambridge.arm.com>
	<EAF47CD23C76F840A9E7FCE10091EFAB02C3CF7D50@dbde02.ent.ti.com>
	<20100216084442.GA3212@n2100.arm.linux.org.uk>
	<5A47E75E594F054BAF48C5E4FC4B92AB03215B07FF@dbde02.ent.ti.com>
Message-ID: <20100220002148.6676a8f6@redhat.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Tue, 16 Feb 2010 14:21:48 +0530
"Gadiyar, Anand" <gadiyar@ti.com> wrote:

> >         hcd->self.uses_dma = (dev->dma_mask != NULL);
> > 
> > Is it easier to make sure that PIO devices don't have dev->dma_mask set?
> 
> 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.

The HC driver does not have to be 100% truthful here. If the system
is not HIGHMEM, HCD can easily set uses_dma to false yet use DMA
by mapping buffers itself, without relying on the quoted code.

On a HIGHMEM system, block layer will bounce-buffer data in such case.
Hopefuly not a problem for ARM?

All network stack drivers work that way, BTW.

-- Pete