linux-kernel - Re: [PATCH 7/8] uio: bind uio_dmem

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Date:	Fri, 15 Jul 2016 10:45:42 +0100
From:	Russell King - ARM Linux <linux@...linux.org.uk>
To:	Anup Patel <anup.patel@...adcom.com>
Cc:	"Hans J. Koch" <hjk@...sjkoch.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jonathan Corbet <corbet@....net>,
	Scott Branden <sbranden@...adcom.com>,
	linux-doc@...r.kernel.org, Ray Jui <rjui@...adcom.com>,
	linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
	bcm-kernel-feedback-list@...adcom.com,
	Ankit Jindal <thatsjindal@...il.com>,
	linux-arm-kernel@...ts.infradead.org,
	Jan Viktorin <viktorin@...ivetech.com>
Subject: Re: [PATCH 7/8] uio: bind uio_dmem_genirq via OF

On Fri, Jul 15, 2016 at 02:34:02PM +0530, Anup Patel wrote:
> +static int uio_dmem_genirq_alloc_platdata(struct platform_device *pdev)
> +{
> +	struct uio_dmem_genirq_pdata pdata;
> +	u32 dma_bits, regions;
> +	u32 sizes[MAX_UIO_MAPS];
> +	int ret;
> +
> +	memset(&pdata, 0, sizeof(pdata));
> +
> +	ret = of_property_read_u32(pdev->dev.of_node,
> +				   uio_of_dma_bits_prop, &dma_bits);
> +	if (ret) {
> +		dev_err(&pdev->dev,
> +			"Missing property %s\n", uio_of_dma_bits_prop);
> +		return ret;
> +	}
> +	if (dma_bits > 64)
> +		dma_bits = 64;
> +
> +	dma_set_coherent_mask(&pdev->dev, DMA_BIT_MASK(dma_bits));

You really need to check the return value from this: this function
negotiates with the architecture, and if 64-bit DMA is not supported,
then the call will fail and you as a driver are expected to fall back
to 32-bit DMA only.

In that case, you're expected to call the same function with a 32-bit
mask, and if that fails, you're supposed to then decide that DMA is
not possible.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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