linux-kernel - Re: [PATCH 3/6] sparc64: Initialize iommu_map_table and iommu

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Date:   Mon, 24 Oct 2016 13:36:54 -0700
From:   tndave <tushar.n.dave@...cle.com>
To:     David Miller <davem@...emloft.net>
Cc:     chris.hyser@...cle.com, sowmini.varadhan@...cle.com,
        vgupta@...opsys.com, robin.murphy@....com, jroedel@...e.de,
        egtvedt@...fundet.no, krzk@...nel.org, rkuo@...eaurora.org,
        sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] sparc64: Initialize iommu_map_table and iommu_pool



On 10/24/2016 10:47 AM, David Miller wrote:
> From: Tushar Dave <tushar.n.dave@...cle.com>
> Date: Mon, 10 Oct 2016 11:12:04 -0700
>
>> Like legacy IOMMU, use common iommu_map_table and iommu_pool for ATU.
>> This change initializes iommu_map_table and iommu_pool for ATU.
>>
>> Signed-off-by: Tushar Dave <tushar.n.dave@...cle.com>
>> Reviewed-by: chris hyser <chris.hyser@...cle.com>
>> Reviewed-by: Sowmini Varadhan <sowmini.varadhan@...cle.com>
>
> I suspect you are adding a bisection problem here.
>
> It looks to me like patch #2 starts setting up to use the ATU
> but these changes in #3 and later are necessary for it to even
> work properly.
>
> You can't leave the tree in an intermediate non-working state
> between changes like that.
I agree but even if you apply only patch #1, #2 things still work using
legacy IOMMU. (and the same is true for rest of the other patches i.e.
#3, #4, #5).

All the patches, except patch #6 , sets up needed data structures and
functions for ATU however ATU will only be used in action after you
apply patch #6 which actually enables 64bit DMA. Until then, things are
going to work using legacy IOMMU with 32bit DMA.

Thanks.

-Tushar
>