From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jacob Pan <jacob.jun.pan-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
Subject: Re: [PATCH v5 07/23] iommu/vt-d: fix dev iotlb pfsid use
Date: Mon, 14 May 2018 13:38:25 -0700
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To: Lu Baolu <baolu.lu-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
Cc: Raj Ashok <ashok.raj-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>, Greg Kroah-Hartman <gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org>, Rafael Wysocki <rafael.j.wysocki-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>, iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>, David Woodhouse <dwmw2-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
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On Mon, 14 May 2018 09:52:04 +0800
Lu Baolu <baolu.lu-VuQAYsv1563Yd54FQh9/CA@public.gmane.org> wrote:

> > diff --git a/drivers/iommu/intel-iommu.c
> > b/drivers/iommu/intel-iommu.c index 4623294..732a10f 100644
> > --- a/drivers/iommu/intel-iommu.c
> > +++ b/drivers/iommu/intel-iommu.c
> > @@ -1459,6 +1459,19 @@ static void iommu_enable_dev_iotlb(struct
> > device_domain_info *info) return;
> >  
> >  	pdev = to_pci_dev(info->dev);
> > +	/* For IOMMU that supports device IOTLB throttling (DIT),
> > we assign
> > +	 * PFSID to the invalidation desc of a VF such that IOMMU
> > HW can gauge
> > +	 * queue depth at PF level. If DIT is not set, PFSID will
> > be treated as
> > +	 * reserved, which should be set to 0.
> > +	 */
> > +	if (!ecap_dit(info->iommu->ecap))
> > +		info->pfsid = 0;
> > +	else if (pdev && pdev->is_virtfn) {
> > +		if (ecap_(info->iommu->ecap))
> > +			dev_warn(&pdev->dev, "SRIOV VF device
> > IOTLB enabled without flow control\n");  
> 
> I can't understand these two lines.
> 
> Isn't the condition always true? What does the error message mean?

you are right, there is no need to check ecap_dit again. thanks!