linux-kernel - Re: [PATCH v4 10/19] iommu: Add set_platform_dma

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Date:   Fri, 6 Jan 2023 14:07:32 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Hector Martin <marcan@...can.st>,
        Sven Peter <sven@...npeter.dev>,
        Rob Clark <robdclark@...il.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Yong Wu <yong.wu@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Orson Zhai <orsonzhai@...il.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Thierry Reding <thierry.reding@...il.com>,
        iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 10/19] iommu: Add set_platform_dma_ops iommu ops

On 1/5/23 9:15 PM, Jason Gunthorpe wrote:
> On Thu, Jan 05, 2023 at 01:58:42PM +0800, Baolu Lu wrote:
>> Hi Jason,
>>
>> On 2023/1/4 21:17, Jason Gunthorpe wrote:
>>> On Wed, Jan 04, 2023 at 08:57:16PM +0800, Lu Baolu wrote:
>>>
>>>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>>>> index de91dd88705b..4e35a9f94873 100644
>>>> --- a/drivers/iommu/iommu.c
>>>> +++ b/drivers/iommu/iommu.c
>>>> @@ -2163,6 +2163,17 @@ static int iommu_group_do_detach_device(struct device *dev, void *data)
>>>>    	return 0;
>>>>    }
>>>> +static int iommu_group_do_set_platform_dma(struct device *dev, void *data)
>>>> +{
>>>> +	const struct iommu_ops *ops = dev_iommu_ops(dev);
>>>> +
>>>> +	if (!ops->set_platform_dma_ops)
>>>> +		return -EINVAL;
>>>> +
>>>> +	ops->set_platform_dma_ops(dev);
>>>> +	return 0;
>>>> +}
>>>> +
>>>>    static int __iommu_group_set_domain(struct iommu_group *group,
>>>>    				    struct iommu_domain *new_domain)
>>>>    {
>>>> @@ -2177,10 +2188,14 @@ static int __iommu_group_set_domain(struct iommu_group *group,
>>>>    	 * platform specific behavior.
>>>>    	 */
>>>>    	if (!new_domain) {
>>>> -		if (WARN_ON(!group->domain->ops->detach_dev))
>>>> -			return -EINVAL;
>>> This should still have the WARN_ON..
>>>
>>> if (WARN_ON(!group->domain->ops->detach_dev && !dev_iommu_ops(dev)->set_platform_dma_ops)
>> This has been implicitly included in the code.
>>
>> iommu_group_do_set_platform_dma() returns -EINVAL if the iommu driver
>> doesn't support set_platform_dma_ops (otherwise always return success).
>> Then, the domain->ops->detach_dev is required and a WARN_ON was there.
>>
>>          if (!new_domain) {
>>                  ret = __iommu_group_for_each_dev(group, NULL,
>>                                  iommu_group_do_set_platform_dma);
>>                  if (ret) {
>>                          if (WARN_ON(!group->domain->ops->detach_dev))
>>                                  return -EINVAL;
>>                          __iommu_group_for_each_dev(group, group->domain,
>>                                  iommu_group_do_detach_device);
>>                  }
>>                  group->domain = NULL;
>>                  return 0;
>>          }
>>
>> Perhaps I should add a comment to explain this?
> But you delete this later when you remove this.
> 
> I think testing the op directly is much clearer, get rid of the whole
> ret and EINVAL thinig:
> 
> if (dev_iommu_ops(dev)->set_platform_dma_ops)
>     __iommu_group_for_each_dev(group, NULL,
>                                   iommu_group_do_set_platform_dma); //	 Can't fail!
> else if (group->domain->ops->detach_dev)
>       __iommu_group_for_each_dev(group, group->domain,
>                                   iommu_group_do_detach_device);
> else
>     WARN(true)

Above looks good to me. Thanks! I have updated this part of code like
below:

@@ -2177,10 +2188,20 @@ static int __iommu_group_set_domain(struct 
iommu_group *group,
          * platform specific behavior.
          */
         if (!new_domain) {
-               if (WARN_ON(!group->domain->ops->detach_dev))
-                       return -EINVAL;
-               __iommu_group_for_each_dev(group, group->domain,
-                                          iommu_group_do_detach_device);
+               struct group_device *grp_dev;
+
+               grp_dev = list_first_entry(&group->devices,
+                                          struct group_device, list);
+
+               if (dev_iommu_ops(grp_dev->dev)->set_platform_dma_ops)
+                       __iommu_group_for_each_dev(group, NULL,
+                                       iommu_group_do_set_platform_dma);
+               else if (group->domain->ops->detach_dev)
+                       __iommu_group_for_each_dev(group, group->domain,
+                                       iommu_group_do_detach_device);
+               else
+                       WARN_ON_ONCE(1);
+
                 group->domain = NULL;
                 return 0;
         }

--
Best regards,
baolu