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

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Date:	Fri, 15 Jul 2016 16:17:50 +0530
From:	Anup Patel <anup.patel@...adcom.com>
To:	Russell King - ARM Linux <linux@...linux.org.uk>
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 <linux-kernel@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>,
	Ankit Jindal <thatsjindal@...il.com>,
	Linux ARM Kernel <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 3:15 PM, Russell King - ARM Linux
<linux@...linux.org.uk> wrote:
> 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.
>

Thanks for pointing out.

I will fix this as-per your suggestion in next revision.

Regards,
Anup