linux-kernel - Re: [PATCH 3/3] powerpc: Dont require a dma

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Message-ID: <20110622125320.79b97a9c@schlenkerla.am.freescale.net>
Date:	Wed, 22 Jun 2011 12:53:20 -0500
From:	Scott Wood <scottwood@...escale.com>
To:	Kumar Gala <galak@...nel.crashing.org>
CC:	Greg KH <greg@...ah.com>, <linuxppc-dev@...abs.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] powerpc: Dont require a dma_ops struct to set dma
 mask

On Wed, 22 Jun 2011 07:02:56 -0500
Kumar Gala <galak@...nel.crashing.org> wrote:

> The only reason to require a dma_ops struct is to see if it has
> implemented set_dma_mask.  If not we can fall back to setting the mask
> directly.
> 
> This resolves an issue with how to sequence the setting of a DMA mask
> for platform devices.  Before we had an issue in that we have no way of
> setting the DMA mask before the various low level bus notifiers get
> called that might check it (swiotlb).
> 
> So now we can do:
> 
> 	pdev = platform_device_alloc("foobar", 0);
> 	dma_set_mask(&pdev->dev, DMA_BIT_MASK(37));
> 	platform_device_register(pdev);

Despite what Documentation/driver-model/platform.txt says, it looks like
platform_device_add() is what you want after platform_device_alloc().
Otherwise device_initialize() gets called twice, as would a call to the
archdata hook if one is added to platform_device_register().

-Scott

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