linux-kernel - Re: [PATCH v3 1/8] iommu: Add MMIO mapping type

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Message-ID: <56BCAF66.8010206@arm.com>
Date:	Thu, 11 Feb 2016 15:57:26 +0000
From:	Robin Murphy <robin.murphy@....com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Niklas Söderlund 
	<niklas.soderlund+renesas@...natech.se>
Cc:	linux-renesas-soc@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	dmaengine@...r.kernel.org, iommu@...ts.linux-foundation.org,
	vinod.koul@...el.com, geert+renesas@...der.be,
	linus.walleij@...aro.org, dan.j.williams@...el.com, arnd@...db.de,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH v3 1/8] iommu: Add MMIO mapping type

On 11/02/16 00:02, Laurent Pinchart wrote:
> Hi Niklas,
>
> Thank you for the patch.
>
> On Wednesday 10 February 2016 01:57:51 Niklas Söderlund wrote:
>> From: Robin Murphy <robin.murphy@....com>
>>
>> On some platforms, MMIO regions might need slightly different treatment
>> compared to mapping regular memory; add the notion of MMIO mappings to
>> the IOMMU API's memory type flags, so that callers can let the IOMMU
>> drivers know to do the right thing.
>>
>> Signed-off-by: Robin Murphy <robin.murphy@....com>
>> Acked-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
>
> Answering the question from the cover letter, yes, it's totally fine to pick
> the ack, that's actually expected.
>
>> ---
>>   drivers/iommu/io-pgtable-arm.c | 4 +++-
>>   include/linux/iommu.h          | 1 +
>
> You might be asked to split this patch in two.

Worse than that, you might also be asked to fix it up when the silly 
author remembers that he did this on a stage-2-only ARM SMMU, and the 
attributes for the stage 1 tables that the IPMMU uses are in a different 
code path:

--->8---
diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index 5b5c299..7622c6e 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -354,7 +354,10 @@ static arm_lpae_iopte arm_lpae_prot_to_pte(struct 
arm_lpae_io_pgtable *data,
                 if (!(prot & IOMMU_WRITE) && (prot & IOMMU_READ))
                         pte |= ARM_LPAE_PTE_AP_RDONLY;

-               if (prot & IOMMU_CACHE)
+               if (prot & IOMMU_MMIO)
+                       pte |= (ARM_LPAE_MAIR_ATTR_IDX_DEV
+                               << ARM_LPAE_PTE_ATTRINDX_SHIFT);
+               else if (prot & IOMMU_CACHE)
                         pte |= (ARM_LPAE_MAIR_ATTR_IDX_CACHE
                                 << ARM_LPAE_PTE_ATTRINDX_SHIFT);
         } else {
--->8---

Sorry for the bother,
Robin.

>>   2 files changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
>> index 381ca5a..3ff4f87 100644
>> --- a/drivers/iommu/io-pgtable-arm.c
>> +++ b/drivers/iommu/io-pgtable-arm.c
>> @@ -364,7 +364,9 @@ static arm_lpae_iopte arm_lpae_prot_to_pte(struct
>> arm_lpae_io_pgtable *data, pte |= ARM_LPAE_PTE_HAP_READ;
>>   		if (prot & IOMMU_WRITE)
>>   			pte |= ARM_LPAE_PTE_HAP_WRITE;
>> -		if (prot & IOMMU_CACHE)
>> +		if (prot & IOMMU_MMIO)
>> +			pte |= ARM_LPAE_PTE_MEMATTR_DEV;
>> +		else if (prot & IOMMU_CACHE)
>>   			pte |= ARM_LPAE_PTE_MEMATTR_OIWB;
>>   		else
>>   			pte |= ARM_LPAE_PTE_MEMATTR_NC;
>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>> index a5c539f..34b6432 100644
>> --- a/include/linux/iommu.h
>> +++ b/include/linux/iommu.h
>> @@ -30,6 +30,7 @@
>>   #define IOMMU_WRITE	(1 << 1)
>>   #define IOMMU_CACHE	(1 << 2) /* DMA cache coherency */
>>   #define IOMMU_NOEXEC	(1 << 3)
>> +#define IOMMU_MMIO	(1 << 4) /* e.g. things like MSI doorbells */
>>
>>   struct iommu_ops;
>>   struct iommu_group;
>