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

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Message-ID: <d30438bf-9add-7904-bad0-0764e3602263@collabora.com>
Date:   Tue, 7 Dec 2021 10:31:58 +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 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.
> 
> 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
> 
> like in [10/33], I added a mtk_iommu_tlb_do_flush_all which don't have
> the pm operation.
> 
> 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.