linux-kernel - Re: [PATCH v3 09/33] iommu/mediatek: Remove for_each_m4u in tlb_sync

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Message-ID: <114af71c-58d0-982f-d362-19184a55fb85@collabora.com>
Date:   Mon, 10 Jan 2022 12:40:18 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Yong Wu <yong.wu@...iatek.com>
Cc:     Joerg Roedel <joro@...tes.org>, Rob Herring <robh+dt@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        Tomasz Figa <tfiga@...omium.org>,
        linux-mediatek@...ts.infradead.org, srv_heupstream@...iatek.com,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org,
        Hsin-Yi Wang <hsinyi@...omium.org>, youlin.pei@...iatek.com,
        anan.sun@...iatek.com, yen-chang.chen@...iatek.com
Subject: Re: [PATCH v3 09/33] iommu/mediatek: Remove for_each_m4u in
 tlb_sync_all

Il 10/01/22 11:59, Yong Wu ha scritto:
> On Mon, 2022-01-10 at 10:16 +0100, AngeloGioacchino Del Regno wrote:
>> Il 09/01/22 03:48, Yong Wu ha scritto:
>>> On Tue, 2022-01-04 at 16:55 +0100, AngeloGioacchino Del Regno
>>> wrote:
>>>> Il 23/09/21 13:58, Yong Wu ha scritto:
>>>>> The tlb_sync_all is called from these three functions:
>>>>> a) flush_iotlb_all: it will be called for each a iommu HW.
>>>>> b) tlb_flush_range_sync: it already has for_each_m4u.
>>>>> c) in irq: When IOMMU HW translation fault, Only need flush
>>>>> itself.
>>>>>
>>>>> Thus, No need for_each_m4u in this tlb_sync_all. Remove it.
>>>>>
>>>>> Signed-off-by: Yong Wu <yong.wu@...iatek.com>
>>>>> ---
>>>>>     drivers/iommu/mtk_iommu.c | 18 +++++++-----------
>>>>>     1 file changed, 7 insertions(+), 11 deletions(-)
>>>>>
>>>>> diff --git a/drivers/iommu/mtk_iommu.c
>>>>> b/drivers/iommu/mtk_iommu.c
>>>>> index 6f4f6624e3ac..0b4c30baa864 100644
>>>>> --- a/drivers/iommu/mtk_iommu.c
>>>>> +++ b/drivers/iommu/mtk_iommu.c
>>>>> @@ -206,19 +206,15 @@ static struct mtk_iommu_domain
>>>>> *to_mtk_domain(struct iommu_domain *dom)
>>>>>     
>>>>>     static void mtk_iommu_tlb_flush_all(struct mtk_iommu_data
>>>>> *data)
>>>>>     {
>>>>> -	struct list_head *head = data->hw_list;
>>>>> -
>>>>> -	for_each_m4u(data, head) {
>>>>> -		if (pm_runtime_get_if_in_use(data->dev) <= 0)
>>>>> -			continue;
>>>>> +	if (pm_runtime_get_if_in_use(data->dev) <= 0)
>>>>> +		return;
>>>>>     
>>>>> -		writel_relaxed(F_INVLD_EN1 | F_INVLD_EN0,
>>>>> -			       data->base + data->plat_data-
>>>>>> inv_sel_reg);
>>>>>
>>>>> -		writel_relaxed(F_ALL_INVLD, data->base +
>>>>> REG_MMU_INVALIDATE);
>>>>> -		wmb(); /* Make sure the tlb flush all done */
>>>>> +	writel_relaxed(F_INVLD_EN1 | F_INVLD_EN0,
>>>>> +		       data->base + data->plat_data-
>>>>>> inv_sel_reg);
>>>>> +	writel_relaxed(F_ALL_INVLD, data->base +
>>>>> REG_MMU_INVALIDATE);
>>>>> +	wmb(); /* Make sure the tlb flush all done */
>>>>
>>>> There aren't a lot of writes here - not anymore, since you are no
>>>> longer doing
>>>> this for_each_m4u()...
>>>> ...so, please change writel_relaxed() to writel() calls, allowing
>>>> you
>>>> to also
>>>> remove the write barrier at the end (since in the non relaxed
>>>> version, order is already ensured).
>>>
>>> In the "writel", the "__iowmb()" runs before "write_relaxed". Then
>>> how
>>> to guarantee the last register was wrote into the HW. Here the
>>> flush
>>> all don't have sync(waiting it complete)
>>>
>>
>> That's right, I'm sorry for the invalid proposal.
>>
>> Though, there's something else to mention here... if writing
>> (F_INVLD_EN1 | F_INVLD_EN0) to inv_sel_reg is *required* to happen
>> before
>> writing F_ALL_INVLD to REG_MMU_INVALIDATE (which I think is exactly
>> the
>> case here), then, in order to ensure write ordering, you should still
>> use
>> writel() instead of the relaxed accessor; after which, since (as you
>> mentioned)
>> there is no sync readback loop, you can keep that wmb() at the end.
> 
> The writel_relaxed also makes sure the order. I did try this:
> 
> 
> https://patchwork.kernel.org/project/linux-mediatek/patch/1570627143-29441-3-git-send-email-yong.wu@mediatek.com/
> 

Ok, that's fair. Means that this patch is fine as it is.
I'll release by R-b on Dafna's patch, as suggested.

Thank you,
- Angelo