Date: Tue, 22 Jun 2004 12:48:39 +0200
Message-ID: <s5heko7na0o.wl@alsa2.suse.de>
From: Takashi Iwai <tiwai@suse.de>
To: Russell King <rmk+lkml@arm.linux.org.uk>
Cc: Matt Porter <mporter@kernel.crashing.org>,
       Jamey Hicks <jamey.hicks@hp.com>, Ian Molton <spyro@f2s.com>,
       linux-kernel@vger.kernel.org, greg@kroah.com, tony@atomide.com,
       david-b@pacbell.net, joshua@joshuawise.com
Subject: Re: DMA API issues
In-Reply-To: <20040622000838.B7802@flint.arm.linux.org.uk>
References: <20040618175902.778e616a.spyro@f2s.com>
	<20040618110721.B3851@home.com>
	<40D3356E.8040800@hp.com>
	<20040618122112.D3851@home.com>
	<20040618204322.C17516@flint.arm.linux.org.uk>
	<s5hoendm3td.wl@alsa2.suse.de>
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At Tue, 22 Jun 2004 00:08:38 +0100,
Russell King wrote:
> 
> On Mon, Jun 21, 2004 at 03:35:42PM +0200, Takashi Iwai wrote:
> > At Fri, 18 Jun 2004 20:43:22 +0100,
> > Russell King wrote:
> > > 
> > > On Fri, Jun 18, 2004 at 12:21:12PM -0700, Matt Porter wrote:
> > > > > page_to_dma so that device specific dma addresses can be constructed.
> > > > 
> > > > A struct device argument to page_to_dma seems like a no brainer to be
> > > > included.
> > > 
> > > Tony Lindgren recently submitted a patch for this:
> > > 
> > > http://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=1931/1
> > > 
> > > which now pending for Linus.  ARM platforms now have three macros to
> > > define if they want to override the default struct page to DMA address
> > > translation.
> > 
> > Wouldn't it be nicer to define a more generic style like
> > 
> > struct page *dma_to_page(struct device *, void *, dma_addr_t)
> 
> What's the 'void *' for?  Hint: this has nothing to do with the virtual
> address and DMA address returned from dma_alloc_coherent().
> 
> page_to_dma - converts a struct page to a DMA address for a given device
> dma_to_virt - converts a DMA address to a CPU direct-mapped virtual address
> virt_to_dma - converts a CPU direct-mapped virtual address to a DMA address

Well, I thought the address handling can be dependent on the device
type, thus passing the both virtual and BUS addresses _might_ help to
calculate the DMA address in some cases.  But forget it, seems
exaggerated.


Takashi
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