linux-kernel - Re: [PATCH v6 07/12] usb: chipidea: add a usb2 driver for ci13xxx

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Date:	Fri, 26 Sep 2014 09:01:49 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Peter Chen <peter.chen@...escale.com>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Antoine Tenart <antoine.tenart@...e-electrons.com>,
	thomas.petazzoni@...e-electrons.com, zmxu@...vell.com,
	devicetree@...r.kernel.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, balbi@...com,
	alexandre.belloni@...e-electrons.com, p.zabel@...gutronix.de,
	jszhang@...vell.com, sebastian.hesselbarth@...il.com
Subject: Re: [PATCH v6 07/12] usb: chipidea: add a usb2 driver for ci13xxx

On Friday 26 September 2014 08:23:40 Peter Chen wrote:
> In current chipidea structure, the parent (glue layer) driver will not be
> used for dma, udc/host driver uses dma mask from child (core layer), at core
> layer we will do:
> 
> 
>         pdev->dev.dma_mask = dev->dma_mask; /* this device is parent */
>         dma_set_coherent_mask(&pdev->dev, dev->coherent_dma_mask);
> 
> Would you suggestion us a suitable way? Or it is ok we use just Antoine's way that
> call dma_coerce_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32)) at parent
> driver no matter dt or non-dt? Thanks.

dma_coerce_mask_and_coherent is not ok, it will force a dma mask that is
unrelated to the actual requirements of the hardware.

I think the best way would be to never use the child device pointer for
DMA operations, just use a pointer to the parent device and make the
child dev->dma_mask pointer NULL to ensure all DMA operations fail.

	Arnd
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