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Date:   Thu, 5 Jan 2023 09:15:53 -0400
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Baolu Lu <baolu.lu@linux.intel.com>
Cc:     Joerg Roedel <joro@8bytes.org>,
        Christoph Hellwig <hch@infradead.org>,
        Kevin Tian <kevin.tian@intel.com>,
        Will Deacon <will@kernel.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
        Hector Martin <marcan@marcan.st>,
        Sven Peter <sven@svenpeter.dev>,
        Rob Clark <robdclark@gmail.com>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
        Andy Gross <agross@kernel.org>,
        Bjorn Andersson <andersson@kernel.org>,
        Yong Wu <yong.wu@mediatek.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Heiko Stuebner <heiko@sntech.de>,
        Matthew Rosato <mjrosato@linux.ibm.com>,
        Orson Zhai <orsonzhai@gmail.com>,
        Baolin Wang <baolin.wang@linux.alibaba.com>,
        Chunyan Zhang <zhang.lyra@gmail.com>,
        Chen-Yu Tsai <wens@csie.org>,
        Thierry Reding <thierry.reding@gmail.com>,
        iommu@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 10/19] iommu: Add set_platform_dma_ops iommu ops
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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)

Jason