linux-kernel - Re: [PATCH v2] iommu/rockchip: Add missing set_platform_dma

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Message-ID: <b5a4a200-e988-99b4-2efc-9dae3a1cb97a@linux.intel.com>
Date:   Fri, 24 Mar 2023 21:31:10 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Steven Price <steven.price@....com>,
        Heiko Stuebner <heiko@...ech.de>,
        Joerg Roedel <joro@...tes.org>, Jason Gunthorpe <jgg@...pe.ca>
Cc:     baolu.lu@...ux.intel.com, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>, iommu@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH v2] iommu/rockchip: Add missing set_platform_dma_ops
 callback

On 2023/3/24 21:24, Steven Price wrote:
> On 24/03/2023 13:16, Baolu Lu wrote:
>> On 2023/3/24 19:11, Steven Price wrote:
>>> Similar to exynos, we need a set_platform_dma_ops() callback for proper
>>> operation on ARM 32 bit after recent changes in the IOMMU framework
>>> (detach ops removal). But also the use of a NULL domain is confusing.
>>>
>>> Rework the code to have a singleton rk_identity_domain which is assigned
>>> to domain when using an identity mapping rather than "detaching". This
>>> makes the code easier to reason about.
>>>
>>> Signed-off-by: Steven Price<steven.price@....com>
>>> ---
>>> Changes since v1[1]:
>>>
>>>    * Reworked the code to avoid a NULL domain, instead a singleton
>>>      rk_identity_domain is used instead. The 'detach' language is no
>>>      longer used.
>>>
>>> [1]
>>> https://lore.kernel.org/r/20230315164152.333251-1-steven.price%40arm.com
>>>
>>>    drivers/iommu/rockchip-iommu.c | 50 ++++++++++++++++++++++++++--------
>>>    1 file changed, 39 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/drivers/iommu/rockchip-iommu.c
>>> b/drivers/iommu/rockchip-iommu.c
>>> index f30db22ea5d7..437541004994 100644
>>> --- a/drivers/iommu/rockchip-iommu.c
>>> +++ b/drivers/iommu/rockchip-iommu.c
>>> @@ -124,6 +124,7 @@ struct rk_iommudata {
>>>      static struct device *dma_dev;
>>>    static const struct rk_iommu_ops *rk_ops;
>>> +static struct iommu_domain rk_identity_domain;
>>>      static inline void rk_table_flush(struct rk_iommu_domain *dom,
>>> dma_addr_t dma,
>>>                      unsigned int count)
>>> @@ -980,26 +981,27 @@ static int rk_iommu_enable(struct rk_iommu *iommu)
>>>        return ret;
>>>    }
>>>    -static void rk_iommu_detach_device(struct iommu_domain *domain,
>>> -                   struct device *dev)
>>> +static int rk_iommu_identity_attach(struct iommu_domain
>>> *identity_domain,
>>> +                    struct device *dev)
>>>    {
>>>        struct rk_iommu *iommu;
>>> -    struct rk_iommu_domain *rk_domain = to_rk_domain(domain);
>>> +    struct rk_iommu_domain *rk_domain;
>>>        unsigned long flags;
>>>        int ret;
>>>          /* Allow 'virtual devices' (eg drm) to detach from domain */
>>>        iommu = rk_iommu_from_dev(dev);
>>>        if (!iommu)
>>> -        return;
>>> +        return -ENODEV;
>>> +
>>> +    rk_domain = to_rk_domain(iommu->domain);
>>>          dev_dbg(dev, "Detaching from iommu domain\n");
>>>    -    /* iommu already detached */
>>> -    if (iommu->domain != domain)
>>> -        return;
>>> +    if (iommu->domain == identity_domain)
>>> +        return 0;
>>>    -    iommu->domain = NULL;
>>> +    iommu->domain = identity_domain;
>> Where did identity_domain come from? Is it rk_identity_domain?
> It's a parameter of the function. In the case of the call in
> rk_iommu_attach_device() then, yes, it's rk_identity_domain. But this
> function is also the "attach_dev" callback of "rk_identity_ops".
> 
> I'll admit this is cargo-culted from Jason's example:
> 
> https://lore.kernel.org/linux-iommu/ZBnef7g7GCxogPNz@ziepe.ca/

Oh! I overlooked that. Thank you for the explanation.

Best regards,
baolu