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

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Date:   Mon, 10 Jan 2022 10:16:03 +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, chao.hao@...iatek.com,
        yen-chang.chen@...iatek.com
Subject: Re: [PATCH v3 09/33] iommu/mediatek: Remove for_each_m4u in
 tlb_sync_all

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.

>>
>>>    
>>> -		pm_runtime_put(data->dev);
>>> -	}
>>> +	pm_runtime_put(data->dev);
>>>    }
>>>    
>>>    static void mtk_iommu_tlb_flush_range_sync(unsigned long iova,
>>> size_t size,
>>>
>