linux-kernel - Re: is_device_dma

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Message-Id: <20090616175549Y.fujita.tomonori@lab.ntt.co.jp>
Date:	Tue, 16 Jun 2009 17:55:59 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	malcolm.blaney@...tek.com.au
Cc:	fujita.tomonori@....ntt.co.jp, linux-kernel@...r.kernel.org
Subject: Re: is_device_dma_capable

On Tue, 16 Jun 2009 17:53:03 +0930
Malcom Blaney <malcolm.blaney@...tek.com.au> wrote:

> Hi Fujita,
> 
> 2009/6/16 FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>:
> > You use X86_32, right?
> 
> I have CONFIG_X86_32=y in my config file.
> 
> >
> > In 2.6.25, X86_32 and X86_64 had the own dma_alloc_coherent
> > implementations; X86_32 accepted a device having dma_mask that is not
> > initialized however X86_64 didn't, I think.
> >
> > When we merged them, we chose to prohibit a device having dma_mask
> > that is not initialized. I'm not sure the DMA docs say this but IMO
> > it's good to require drivers to set up dma_mask (and
> > coherent_dma_mask) properly if the drivers want DMA.
> >
> 
> If you could point me in the direction of how to set these values
> correctly, I would appreciate it.

You hit the problem that a device that parport_pc_probe_port creates
but doesn't set up the dma_mask properly, right (I'm not familiar with
the driver at all so I might misunderstand something)?

If so, I guess that the following patch works (only compile tested).


diff --git a/drivers/parport/parport_pc.c b/drivers/parport/parport_pc.c
index 151bf5b..1af57b7 100644
--- a/drivers/parport/parport_pc.c
+++ b/drivers/parport/parport_pc.c
@@ -2271,6 +2271,9 @@ struct parport *parport_pc_probe_port(unsigned long int base,
 		if (IS_ERR(pdev))
 			return NULL;
 		dev = &pdev->dev;
+
+		dev->coherent_dma_mask = DMA_BIT_MASK(24);
+		dev->dma_mask = &dev->coherent_dma_mask;
 	}
 
 	ops = kmalloc(sizeof(struct parport_operations), GFP_KERNEL);
--
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