linux-kernel - Re: [RFC PATCH v2 03/15] arm64: mm: change IOMMU notifier action to attach DMA ops

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Date:	Thu, 23 Jun 2016 12:32:12 +0100
From:	Robin Murphy <robin.murphy@....com>
To:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:	Jon Masters <jcm@...hat.com>, Marc Zyngier <marc.zyngier@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	linux-kernel@...r.kernel.org, Will Deacon <will.deacon@....com>,
	Sinan Kaya <okaya@...eaurora.org>, linux-acpi@...r.kernel.org,
	iommu@...ts.linux-foundation.org,
	Hanjun Guo <hanjun.guo@...aro.org>, linux-pci@...r.kernel.org,
	Tomasz Nowicki <tn@...ihalf.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH v2 03/15] arm64: mm: change IOMMU notifier action to
 attach DMA ops

Hi Lorenzo,

On 17/06/16 15:15, Lorenzo Pieralisi wrote:
>> I think this patch makes sense even independent of the rest of the
>> series, one nit inline notwithstanding.
>
> Thanks. Yes I added it to this series since it is not strictly
> necessary (ie it does not fix anything) in the mainline, but
> it *is* necessary for this whole series to function when we
> boot through ACPI.
>
> I will send it out in a separate patch and fold changes you
> request below, it would be good to have some coverage for
> it before merging it.

Having considered it a bit more, triggering on BIND_DRIVER also means 
the silly "process the whole list every time" behaviour should go away. 
There's little point in trying to configure a device's ops before we 
know they're actually needed, and once a driver has bound it's too late 
to change anything anyway. What do you think of squashing in something 
like the below?

Robin.

----->8-----
diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
index 7d3fa9ae8a11..02484dc3f369 100644
--- a/arch/arm64/mm/dma-mapping.c
+++ b/arch/arm64/mm/dma-mapping.c
@@ -854,10 +854,11 @@ static int __iommu_attach_notifier(struct 
notifier_block *nb,

  	mutex_lock(&iommu_dma_notifier_lock);
  	list_for_each_entry_safe(master, tmp, &iommu_dma_masters, list) {
-		if (do_iommu_attach(master->dev, master->ops,
-				master->dma_base, master->size)) {
+		if (data == master->dev && do_iommu_attach(master->dev,
+				master->ops, master->dma_base, master->size)) {
  			list_del(&master->list);
  			kfree(master);
+			break;
  		}
  	}
  	mutex_unlock(&iommu_dma_notifier_lock);