linux-kernel - Re: [PATCH] iommu/intel: Enable pci capabilities before assigning cache tags

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Message-ID: <20240626134301.y3es4r4go5736mi6@joelS2.panther.com>
Date: Wed, 26 Jun 2024 15:43:01 +0200
From: Joel Granados <j.granados@...sung.com>
To: Baolu Lu <baolu.lu@...ux.intel.com>
CC: David Woodhouse <dwmw2@...radead.org>, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
	<iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iommu/intel: Enable pci capabilities before assigning
 cache tags

On Wed, Jun 26, 2024 at 09:09:04AM +0800, Baolu Lu wrote:
> On 6/25/24 9:49 PM, Joel Granados via B4 Relay wrote:
> > From: Joel Granados<j.granados@...sung.com>
> > 
> > Enable the pci capabilities by calling iommu_enable_pci_caps before we
> > assign a cache tag. The cache_tag_assign_domain call in
> > dmar_domain_attach_device uses the device_domain_info->ats_enabled
> > element to decide on the cache_tag_type value. Therefore ats_enabled
> > needs to be evaluated before the call to the tag cache assignment.
> > 
> > Signed-off-by: Joel Granados<j.granados@...sung.com>
> > ---
> > The "what" and "why" are included in the commit message.
> > 
> > Tried to place cache_tag_assign_domain before the early return in
> > "if(dev_is_real_dma_subdevice(dev))". This means that the call to
> > iommu_enable_pci_caps landed before the setup functions [1] which is not
> > an issue as they seem to be orthogonal (I would like to be proven wrong
> > here).
> > 
> > An alternative to this patch would be to use a different way of checking
> > if the device is ATS enabled in __cache_tag_assign_domain.
> > 
> > Comments greatly appreciated
> 
> Thank you very much for the patch. But we already have a similar patch
> which has been picked by Joerg for 6.10-rc.
> 
> https://lore.kernel.org/linux-iommu/20240620062940.201786-1-baolu.lu@linux.intel.com/
Completely missed this. I'll give it a try tomorrow and report back.

Best

-- 

Joel Granados