linux-kernel - Re: [PATCH v2 09/13] iommu/rockchip: Use iommu_group_get_for_dev() for add

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Date:   Wed, 17 Jan 2018 20:47:22 +0800
From:   JeffyChen <jeffy.chen@...k-chips.com>
To:     Robin Murphy <robin.murphy@....com>, linux-kernel@...r.kernel.org
CC:     jcliang@...omium.org, xxm@...k-chips.com, tfiga@...omium.org,
        Heiko Stuebner <heiko@...ech.de>,
        linux-rockchip@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 09/13] iommu/rockchip: Use iommu_group_get_for_dev()
 for add_device

Hi Robin,

On 01/17/2018 08:31 PM, Robin Murphy wrote:
> On 16/01/18 13:25, Jeffy Chen wrote:
>> IOMMU drivers are supposed to call this function instead of manually
>> creating a group in their .add_device callback. This behavior is not
>> strictly required by ARM DMA mapping implementation, but ARM64 already
>> relies on it. This patch fixes the rockchip-iommu driver to comply with
>> this requirement.
>
> FWIW that's not 100% true: what arm64 relies on is the group having a
> default DMA ops domain. Technically, you *could* open-code that in the
> driver's group allocation, but obviously using the appropriate existing
> API is nicer :)
ok, will rewrite the commit message.
>
> [...]
>> @@ -1182,6 +1164,29 @@ static void rk_iommu_remove_device(struct
>> device *dev)
>>       iommu_group_remove_device(dev);
>>   }
>> +static struct iommu_group *rk_iommu_device_group(struct device *dev)
>> +{
>> +    struct iommu_group *group;
>> +    int ret;
>> +
>> +    group = iommu_group_get(dev);
>> +    if (!group) {
>
> This check is pointless - if dev->iommu_group were non-NULL you wouldn't
> have been called in the first place.
right, it's allocated in the probe.
>
> Robin.