linux-kernel - Re: [PATCH v2 13/13] iommu/rockchip: Support sharing IOMMU between masters

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Message-ID: <5A5F5050.5040308@rock-chips.com>
Date:   Wed, 17 Jan 2018 21:32:00 +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 13/13] iommu/rockchip: Support sharing IOMMU between
 masters

Hi Robin,

On 01/17/2018 09:00 PM, Robin Murphy wrote:
> On 16/01/18 13:25, Jeffy Chen wrote:
>> There would be some masters sharing the same IOMMU device. Put them in
>> the same iommu group and share the same iommu domain.
>>
>> Signed-off-by: Jeffy Chen <jeffy.chen@...k-chips.com>
>> ---
>>
>> Changes in v2: None
>>
>>   drivers/iommu/rockchip-iommu.c | 39
>> +++++++++++++++++++++++++++++++--------
>>   1 file changed, 31 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/iommu/rockchip-iommu.c
>> b/drivers/iommu/rockchip-iommu.c
>> index c8de1456a016..6c316dd0dd2d 100644
>> --- a/drivers/iommu/rockchip-iommu.c
>> +++ b/drivers/iommu/rockchip-iommu.c
>> @@ -100,11 +100,13 @@ struct rk_iommu {
>>       struct iommu_device iommu;
>>       struct list_head node; /* entry in rk_iommu_domain.iommus */
>>       struct iommu_domain *domain; /* domain to which iommu is
>> attached */
>> +    struct iommu_group *group;
>>       struct mutex pm_mutex; /* serializes power transitions */
>>   };
>>   struct rk_iommudata {
>>       struct device_link *link; /* runtime PM link from IOMMU to
>> master */
>> +    struct iommu_domain *domain; /* domain to which device is
>> attached */
>
> I don't see why this is needed - for example, mtk_iommu does the same
> thing without needing to track the active domain in more than one place.
>
> Fundamentally, for this kind of IOMMU without the notion of multiple
> translation contexts, the logic should look like:
>
>      iommudrv_attach_device(dev, domain) {
>          iommu = dev_get_iommu(dev);
>          if (iommu->curr_domain != domain) {
>              update_hw_state(iommu, domain);
>              iommu->curr_domain = domain;
>          }
>      }
>
> which I think is essentially what you have anyway. When a group contains
> multiple devices, you update the IOMMU state for the first device, then
> calls for subsequent devices in the group do nothing since they see the
> IOMMU state is already up-to-date with the new domain.
>
right, will remove it.
> Robin.