Re: [RESEND PATCH v2 14/15] ASoC: qcom: apq8096: Add db820c machine driver

[Stephen Boyd <sboyd@codeaurora.org>]

On 01/03, Srinivas Kandagatla wrote:
> Thanks for your review comments,
> 
> On 03/01/18 17:20, Stephen Boyd wrote:
> >>+
> >>+	return ret;
> >>+}
> >>+
> >>+static int msm_snd_apq8096_probe(struct platform_device *pdev)
> >>+{
> >>+	int ret;
> >>+	struct snd_soc_card *card;
> >>+
> >>+	card = devm_kzalloc(&pdev->dev, sizeof(*card), GFP_KERNEL);
> >>+	if (!card)
> >>+		return -ENOMEM;
> >>+
> >>+	card->dev = &pdev->dev;
> >>+
> >>+	ret = dma_coerce_mask_and_coherent(card->dev, DMA_BIT_MASK(32));
> >
> >Why do we need to do this? Can you add some sort of comment in the code
> >about why?
> 
> Even though dsp supports 64 bit addresses, but the sid sits at
> offset of 32, which brings this restriction of supporting only 32
> bit iova.
> 

Doesn't the dsp have an iommu in place to make the address
translation from 64 to 32 bits transparent? I thought this was
what dma-ranges and iommu binding was for, but I'm not well
versed on all the details here.

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