linux-kernel - Re: [PATCH 1/2] iommu/mediatek: Always tlb_flush

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Message-ID: <35d53ea0-68db-a516-9e9c-272e8f0ed082@collabora.com>
Date:   Wed, 8 Dec 2021 11:50:04 +0200
From:   Dafna Hirschfeld <dafna.hirschfeld@...labora.com>
To:     Yong Wu <yong.wu@...iatek.com>
Cc:     kernel@...labora.com, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "moderated list:MEDIATEK IOMMU DRIVER" 
        <linux-mediatek@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>,
        linux-media@...r.kernel.org, sebastian.reichel@...labora.com,
        iommu@...ts.linux-foundation.org
Subject: Re: [PATCH 1/2] iommu/mediatek: Always tlb_flush_all when each PM
 resume



On 07.12.21 10:31, Dafna Hirschfeld wrote:
> 
> 
> On 27.11.21 04:46, Yong Wu wrote:
>> Hi Dafna,
>>
>> Sorry for reply late.
>>
>> On Mon, 2021-11-22 at 12:43 +0200, Dafna Hirschfeld wrote:
>>> From: Yong Wu <yong.wu@...iatek.com>
>>>
>>> Prepare for 2 HWs that sharing pgtable in different power-domains.
>>>
>>> When there are 2 M4U HWs, it may has problem in the flush_range in
>>> which
>>> we get the pm_status via the m4u dev, BUT that function don't reflect
>>> the
>>> real power-domain status of the HW since there may be other HW also
>>> use
>>> that power-domain.
>>>
>>> The function dma_alloc_attrs help allocate the iommu buffer which
>>> need the corresponding power domain since tlb flush is needed when
>>> preparing iova. BUT this function only is for allocating buffer,
>>> we have no good reason to request the user always call pm_runtime_get
>>> before calling dma_alloc_xxx. Therefore, we add a tlb_flush_all
>>> in the pm_runtime_resume to make sure the tlb always is clean.
>>>
>>> Another solution is always call pm_runtime_get in the
>>> tlb_flush_range.
>>> This will trigger pm runtime resume/backup so often when the iommu
>>> power is not active at some time(means user don't call pm_runtime_get
>>> before calling dma_alloc_xxx), This may cause the performance drop.
>>> thus we don't use this.
>>>
>>> In other case, the iommu's power should always be active via device
>>> link with smi.
>>>
>>> The previous SoC don't have PM except mt8192. the mt8192 IOMMU is
>>> display's
>>> power-domain which nearly always is enabled. thus no need fix tags
>>> here.
>>> Prepare for mt8195.
>>
>> In this patchset, this message should be not proper. I think you could
>> add the comment why this patch is needed in mt8173.
>>
>>>
>>> Signed-off-by: Yong Wu <yong.wu@...iatek.com>
>>> [imporvie inline doc]
>>> Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@...labora.com>
>>> ---
>>>   drivers/iommu/mtk_iommu.c | 7 +++++++
>>>   1 file changed, 7 insertions(+)
>>>
>>> diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
>>> index 25b834104790..28dc4b95b6d9 100644
>>> --- a/drivers/iommu/mtk_iommu.c
>>> +++ b/drivers/iommu/mtk_iommu.c
>>> @@ -964,6 +964,13 @@ static int __maybe_unused
>>> mtk_iommu_runtime_resume(struct device *dev)
>>>           return ret;
>>>       }
>>> +    /*
>>> +     * Users may allocate dma buffer before they call
>>> pm_runtime_get,
>>> +     * in which case it will lack the necessary tlb flush.
>>> +     * Thus, make sure to update the tlb after each PM resume.
>>> +     */
>>> +    mtk_iommu_tlb_flush_all(data);
>>
>> This should not work. since current the *_tlb_flush_all call
>> pm_runtime_get_if_in_use which will always return 0 when it called from
>> this runtime_cb in my test. thus, It won't do the tlb_flush_all
>> actually.

He, indeed, my mistake, although the encoder works more or less fine even
without the full flush so I didn't catch that.

>>
>> I guess this also depend on these two patches of mt8195 v3.
>> [PATCH v3 09/33] iommu/mediatek: Remove for_each_m4u in tlb_sync_all
>> [PATCH v3 10/33] iommu/mediatek: Add tlb_lock in tlb_flush_all

I'll add those two

>>
>> like in [10/33], I added a mtk_iommu_tlb_do_flush_all which don't have
>> the pm operation.

yes, I need to remove the pm_runtime_get_if_in_use call in the 'flush_all' func
I see there is also a patch for that in the mt8195 v3 series "[PATCH v3 13/33] iommu/mediatek: Remove the power status checking in tlb flush all"

So I'll send v2, adding all those 3 patches, but I think adding mtk_iommu_tlb_do_flush_all
on patch 9 and removing it again on patch 13 is confusing so I'll avoid that.

Thanks,
Dafna



>>
>> This looks has a dependence. Let me know if I can help this.
> 
> It did work for me, testing on elm device. I'll check that again.
> 
> 
>>
>>> +
>>>       /*
>>>        * Uppon first resume, only enable the clk and return, since
>>> the values of the
>>>        * registers are not yet set.
>