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

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Date:   Thu, 4 Nov 2021 11:28:38 +0800
From:   Yong Wu <yong.wu@...iatek.com>
To:     Dafna Hirschfeld <dafna.hirschfeld@...labora.com>
CC:     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>,
        Collabora Kernel ML <kernel@...labora.com>,
        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>
Subject: Re: [PATCH v3 13/33] iommu/mediatek: Remove the power status
 checking in tlb flush all

On Mon, 2021-10-25 at 12:03 +0800, Yong Wu wrote:
> On Fri, 2021-10-22 at 16:03 +0200, Dafna Hirschfeld wrote:
> > Hi
> > 
> > 
> > On 23.09.21 13:58, Yong Wu wrote:
> > > 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
> > 
> > Regarding case "c) tlb flush range fail case", I found out that
> > this
> > often happens when the iommu is used while it is runtime
> > suspended. 
> 
> Which SoC and branch are you testing on?
> 
> > For example the mtk-vcodec encoder driver calls
> > "pm_runtime_resume_and_get" only when it starts
> > streaming but
> > buffers allocation is done in 'v4l2_reqbufs' before
> > "pm_runtime_resume_and_get" is called
> 
> This is the case I tried to fix in [14/33].
> pm_runtime_get_if_in_use should return when the iommu device's pm is
> not active when vcodec allocate buffer before pm_runtime_resume_and
> get.
> 
> Do you have the devicelink patchset in your branch? if not, the
> vcodec
> should call mtk_smi_larb_get to enable the power/clock for larbs,
> then
> the iommu's device is active via devicelink between smi and iommu
> device.
> 
> > and then I see the warning "Partial TLB flush timed out, falling
> > back
> > to full flush"
> > I am not sure how to fix that issue, but it seems that case 'c)'

Have your issue been fixed? or more information about it.

Thanks.

> > might indicate that
> > power and clock are actually not enabled.
> > 
> > > 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.
> > > 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(-)