linux-kernel - Re: [PATCH v3 13/33] iommu/mediatek: Remove the power status checking in tlb flush all

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Message-ID: <c5062c4636e67924af8fbf9a66565e2f89dddce5.camel@mediatek.com>
Date:   Sun, 9 Jan 2022 10:47:24 +0800
From:   Yong Wu <yong.wu@...iatek.com>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.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 13/33] iommu/mediatek: Remove the power status
 checking in tlb flush all

On Tue, 2022-01-04 at 16:55 +0100, AngeloGioacchino Del Regno wrote:
> Il 23/09/21 13:58, Yong Wu ha scritto:
> > To simplify the code, Remove the power status checking in the
> > tlb_flush_all, remove this:
> >     if (pm_runtime_get_if_in_use(data->dev) <= 0)
> > 	    continue;
> > 
> > After this patch, the mtk_iommu_tlb_flush_all will be called from
> > a) isr
> > b) pm runtime resume callback
> > c) tlb flush range fail case
> > d) iommu_create_device_direct_mappings
> >     -> iommu_flush_iotlb_all
> > In first three cases, the power and clock always are enabled; d) is
> > direct
> > mapping, the tlb flush is unnecessay since we already have
> > tlb_flush_all
> > in the pm_runtime_resume callback. When the iommu's power status is
> > changed to active, the tlb always is clean.
> > 
> > In addition, there still are 2 reasons that don't add PM status
> > checking
> > in the tlb flush all:
> > a) Write tlb flush all register also is ok even though the HW has
> > no
> > power and clocks. Write ignore.
> 
> Do you mean that the register write seemingly succeeds but the
> hardware discards it?
> Please, reword the `a` sentence to be clearer.

Yes. This is the "Write ignore" I tried to explain.

By the way, the tlb operation patches were moved to this patchset[1]
from Dafna. Would you help take a look at that one? I will send the
next mt8195 version based on that patchset.

[1] 
https://lore.kernel.org/linux-mediatek/20211208120744.2415-1-dafna.hirschfeld@collabora.com/

Thanks.

> 
> > b) pm_runtime_get_if_in_use(m4udev) is 0 when the tlb_flush_all
> > is called frm pm_runtime_resume cb. From this point, we can not add
> > this code above in this tlb_flush_all.
> > 
> > Signed-off-by: Yong Wu <yong.wu@...iatek.com>
> > ---
> >   drivers/iommu/mtk_iommu.c | 20 +++++++-------------
> >   1 file changed, 7 insertions(+), 13 deletions(-)
> > 
> > diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> > index e9e94944ed91..4a33b6c6b1db 100644
> > --- a/drivers/iommu/mtk_iommu.c
> > +++ b/drivers/iommu/mtk_iommu.c
> > @@ -204,10 +204,14 @@ static struct mtk_iommu_domain
> > *to_mtk_domain(struct iommu_domain *dom)
> >   	return container_of(dom, struct mtk_iommu_domain, domain);
> >   }
> >   
> > -static void mtk_iommu_tlb_do_flush_all(struct mtk_iommu_data
> > *data)
> > +static void mtk_iommu_tlb_flush_all(struct mtk_iommu_data *data)
> >   {
> >   	unsigned long flags;
> >   
> > +	/*
> > +	 * No need get power status since the HW PM status nearly is
> > active
> > +	 * when entering here.
> 
> Please reword this comment to explain the entire situation.
> 
> > +	 */
> >   	spin_lock_irqsave(&data->tlb_lock, flags);
> >   	writel_relaxed(F_INVLD_EN1 | F_INVLD_EN0,
> >   		       data->base + data->plat_data->inv_sel_reg);
> > @@ -216,16 +220,6 @@ static void mtk_iommu_tlb_do_flush_all(struct
> > mtk_iommu_data *data)
> >   	spin_unlock_irqrestore(&data->tlb_lock, flags);
> >   }
> >   
> > -static void mtk_iommu_tlb_flush_all(struct mtk_iommu_data *data)
> > -{
> > -	if (pm_runtime_get_if_in_use(data->dev) <= 0)
> > -		return;
> > -
> > -	mtk_iommu_tlb_do_flush_all(data);
> > -
> > -	pm_runtime_put(data->dev);
> > -}
> > -
> >   static void mtk_iommu_tlb_flush_range_sync(unsigned long iova,
> > size_t size,
> >   					   struct mtk_iommu_data *data)
> >   {
> > @@ -263,7 +257,7 @@ static void
> > mtk_iommu_tlb_flush_range_sync(unsigned long iova, size_t size,
> >   		if (ret) {
> >   			dev_warn(data->dev,
> >   				 "Partial TLB flush timed out, falling
> > back to full flush\n");
> > -			mtk_iommu_tlb_do_flush_all(data);
> > +			mtk_iommu_tlb_flush_all(data);
> >   		}
> >   
> >   		if (has_pm)
> > @@ -993,7 +987,7 @@ static int __maybe_unused
> > mtk_iommu_runtime_resume(struct device *dev)
> >   	 *
> >   	 * Thus, Make sure the tlb always is clean after each PM
> > resume.
> >   	 */
> > -	mtk_iommu_tlb_do_flush_all(data);
> > +	mtk_iommu_tlb_flush_all(data);
> >   
> >   	/*
> >   	 * Uppon first resume, only enable the clk and return, since
> > the values of the
> > 
> 
>