DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws;
  s=s1024; d=pacbell.net;
  h=Received:X-YMail-OSG:From:To:Subject:Date:User-Agent:Cc:References:In-Reply-To:MIME-Version:Content-Type:Content-Transfer-Encoding:Content-Disposition:Message-Id;
  b=enbsduArJC9kqAiIpLxRKEWjhth7swU94F83oBsbJp9e8KX5/65JJBvno8aKXveRCITryQB0caA8FizpEBPD6L/k8PFuG+AMSlgix2ME4n1z2qx+7eJM18ZwJfxU/kP0w3y5mZ1wppFAA+P+oDgiMfaC6wEF6KFeVm8tTxigBHg=  ;
From: David Brownell <david-b@pacbell.net>
To: "=?iso-8859-1?q?H=E5vard?= Skinnemoen" <hskinnemoen@gmail.com>
Subject: Re: [PATCH] atmel_spi: Pass correct DMA address to controller
Date: Wed, 30 May 2007 10:27:17 -0700
User-Agent: KMail/1.9.6
Cc: "Haavard Skinnemoen" <hskinnemoen@atmel.com>, wux@landicorp.com,
       linux-kernel@vger.kernel.org
References: <11793107892086-git-send-email-hskinnemoen@atmel.com> <200705161254.59308.david-b@pacbell.net> <1defaf580705161414i67e753d7x883a78da347f7d55@mail.gmail.com>
In-Reply-To: <1defaf580705161414i67e753d7x883a78da347f7d55@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain;
  charset="iso-8859-1"
Content-Transfer-Encoding: 8bit
Content-Disposition: inline
Message-Id: <200705301027.17678.david-b@pacbell.net>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1558
Lines: 45

I think I'll sign off on this as-is.


On Wednesday 16 May 2007, H?vard Skinnemoen wrote:
> On 5/16/07, David Brownell <david-b@pacbell.net> wrote:

> > It's legit to set up cpu-virtual (for PIO) and dma addresses
> > for each buffer, since the upper layer driver has no way to
> > know if the underlying controller driver is DMA-capable, or
> > for that matter PIO-capable.
> 
> Yes, but are there any drivers that will provide a valid dma address
> and a NULL cpu-virtual pointer?

Potentially.  One scenario would be a block driver, which needs to
work with scatterlists.  dma_map_sg() is allowed to coalesce the
scatterlist entries, as with an IOMMU.  If it does that, there can
no longer be a one-to-one linkage between addreses provided to that
driver, and the dma addresess.  (Likewise, addresses in HIGHMEM are
not normally going to have kernel virtual addresses.)  So providing
both types of address is no longer practical with scatterlists.


> 		That would indeed break my 
> assumptions, but it would also break any PIO-only drivers, wouldn't
> it?

Which is exactly why the current "mmc_spi" code doesn't use the
dma_map_sg() interface.  Instead, it goes in more byte-size chunks,
taking care to provide both dma and pio addresses.  It's a PITA,
but at least it's coded now.

- Dave


> Haavard
> 


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/