linux-kernel - Re: [PATCH 1/1] USB: ehci-omap: Reset dma

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Date:	Mon, 3 Jun 2013 10:51:08 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Roger Quadros <rogerq@...com>
Cc:	Alan Stern <stern@...land.harvard.edu>, balbi@...com,
	linux-usb@...r.kernel.org, linux-omap@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree-discuss@...ts.ozlabs.org
Subject: Re: [PATCH 1/1] USB: ehci-omap: Reset dma_mask pointer on probe

On Thu, May 23, 2013 at 05:46:44PM +0300, Roger Quadros wrote:
> On 05/23/2013 05:11 PM, Alan Stern wrote:
> > On Thu, 23 May 2013, Roger Quadros wrote:
> > 
> >> Device tree probed devices don't get dma_mask set. Previously
> >> we were setting the dma_mask pointer only if it was NULL.
> >> However, the address of 'omap_ehci_dma_mask' would change
> >> each time the module is unloaded and loaded back thus causing
> >> the devices dma_mask pointer to be invalid on the next load.
> >>
> >> This will cause page faults if any driver tries to access the
> >> old dma_mask pointer.
> >>
> >> Unconditionally re-setting the dma_mask pointer fixes this problem.
> > 
> >> diff --git a/drivers/usb/host/ehci-omap.c b/drivers/usb/host/ehci-omap.c
> >> index 3d1491b..b33e306 100644
> >> --- a/drivers/usb/host/ehci-omap.c
> >> +++ b/drivers/usb/host/ehci-omap.c
> >> @@ -146,8 +146,7 @@ static int ehci_hcd_omap_probe(struct platform_device *pdev)
> >>  	 * Since shared usb code relies on it, set it here for now.
> >>  	 * Once we have dma capability bindings this can go away.
> >>  	 */
> >> -	if (!pdev->dev.dma_mask)
> >> -		pdev->dev.dma_mask = &omap_ehci_dma_mask;
> >> +	pdev->dev.dma_mask = &omap_ehci_dma_mask;
> > 
> > Is this the solution that people have agreed on?  There has been a lot 
> > of discussion on this topic.  In particular, there has been talk about 
> > fixing it in the DT core.
> 
> Fixing it in DT core would be best.

Then please do that.

thanks,

greg k-h
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