linux-kernel - Re: [PATCH v5 1/2] usb: make xhci platform driver use 64 bit or 32 bit DMA

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Date:	Thu, 20 Aug 2015 15:09:11 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Duc Dang <dhdang@....com>
Cc:	linux-arm <linux-arm-kernel@...ts.infradead.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Feng Kan <fkan@....com>, Mark Langsdorf <mlangsdo@...hat.com>,
	mathias.nyman@...el.com, Greg KH <gregkh@...uxfoundation.org>,
	USB list <linux-usb@...r.kernel.org>,
	patches <patches@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Loc Ho <lho@....com>
Subject: Re: [PATCH v5 1/2] usb: make xhci platform driver use 64 bit or 32 bit DMA

On Wednesday 19 August 2015 14:28:33 Duc Dang wrote:
> 
> Hi Arnd,
> 
> So the check will look like this, please let me know what do you think:
>         if (!pdev->dev.dma_mask) {
>                 WARN_ON(1);
>                 /* Initialize dma_mask if the broken platform code has
> not done so */
>                 pdev->dev.dma_mask = &pdev->dev.coherent_dma_mask;
>         }

The condition can be written as 

	if (WARN_ON(!pdev->dev.dma_mask))

and I'd use dma_coerce_mask_and_coherent() instead of manually setting the
pointer, as an annotation for the fact that we are knowingly violating the
API here.

Those two points are just cosmetic though, aside from them, your code
above is what I had in mind.

Thanks,

	Arnd
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