linux-kernel - Re: [PATCH v2] iommu/arm: Add module parameter to set msi iova address

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Message-ID: <f2de12f9-b53b-abcd-4133-7bcb90341f0c@linux.microsoft.com>
Date:   Tue, 22 Sep 2020 15:37:08 -0700
From:   Vennila Megavannan <vemegava@...ux.microsoft.com>
To:     Will Deacon <will@...nel.org>
Cc:     robin.murphy@....com, joro@...tes.org, srinath.mannam@...adcom.com,
        jean-philippe@...aro.org, eric.auger@...hat.com,
        shameerali.kolothum.thodi@...wei.com, tyhicks@...ux.microsoft.com,
        linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com
Subject: Re: [PATCH v2] iommu/arm: Add module parameter to set msi iova
 address

Sure, that's a great suggestion, I'll rework on the patch and post again.

Vennila

On 9/21/2020 1:45 PM, Will Deacon wrote:
> On Mon, Sep 14, 2020 at 11:13:07AM -0700, Vennila Megavannan wrote:
>> From: Srinath Mannam <srinath.mannam@...adcom.com>
>>
>> Add provision to change default value of MSI IOVA base to platform's
>> suitable IOVA using module parameter. The present hardcoded MSI IOVA base
>> may not be the accessible IOVA ranges of platform.
>>
>> If any platform has the limitaion to access default MSI IOVA, then it can
>> be changed using "arm-smmu.msi_iova_base=0xa0000000" command line argument.
>>
>> Signed-off-by: Srinath Mannam <srinath.mannam@...adcom.com>
>> Co-developed-by: Vennila Megavannan <vemegava@...ux.microsoft.com>
>> Signed-off-by: Vennila Megavannan <vemegava@...ux.microsoft.com>
>> ---
>>   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 5 ++++-
>>   drivers/iommu/arm/arm-smmu/arm-smmu.c       | 5 ++++-
>>   2 files changed, 8 insertions(+), 2 deletions(-)
> This feels pretty fragile. Wouldn't it be better to realise that there's
> a region conflict with iommu_dma_get_resv_regions() and move the MSI window
> accordingly at runtime?
>
> Will