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

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Message-ID: <e595cb26-e48b-335a-28bc-353a2a7d641a@linaro.org>
Date:   Thu, 4 Jan 2018 09:25:24 +0000
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Stephen Boyd <sboyd@...eaurora.org>
Cc:     Andy Gross <andy.gross@...aro.org>,
        Mark Brown <broonie@...nel.org>, linux-arm-msm@...r.kernel.org,
        alsa-devel@...a-project.org, David Brown <david.brown@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Patrick Lai <plai@...eaurora.org>,
        Banajit Goswami <bgoswami@...eaurora.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, linux-soc@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [RESEND PATCH v2 14/15] ASoC: qcom: apq8096: Add db820c machine
 driver



On 03/01/18 19:41, Stephen Boyd wrote:
>>>> +	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.
Thanks for reminding, dma-ranges would work too, I will give that a go 
in next version.

--srini