Re: [PATCH v5 18/27] iommu/mediatek: Add power-domain operation

[Tomasz Figa <tfiga@chromium.org>]

On Tue, Dec 29, 2020 at 8:06 PM Yong Wu <yong.wu@mediatek.com> wrote:
>
> On Wed, 2020-12-23 at 17:36 +0900, Tomasz Figa wrote:
> > On Wed, Dec 09, 2020 at 04:00:53PM +0800, Yong Wu wrote:
> > > In the previous SoC, the M4U HW is in the EMI power domain which is
> > > always on. the latest M4U is in the display power domain which may be
> > > turned on/off, thus we have to add pm_runtime interface for it.
> > >
> > > When the engine work, the engine always enable the power and clocks for
> > > smi-larb/smi-common, then the M4U's power will always be powered on
> > > automatically via the device link with smi-common.
> > >
> > > Note: we don't enable the M4U power in iommu_map/unmap for tlb flush.
> > > If its power already is on, of course it is ok. if the power is off,
> > > the main tlb will be reset while M4U power on, thus the tlb flush while
> > > m4u power off is unnecessary, just skip it.
> > >
> > > There will be one case that pm runctime status is not expected when tlb
> > > flush. After boot, the display may call dma_alloc_attrs before it call
> > > pm_runtime_get(disp-dev), then the m4u's pm status is not active inside
> > > the dma_alloc_attrs. Since it only happens after boot, the tlb is clean
> > > at that time, I also think this is ok.
> > >
> > > Signed-off-by: Yong Wu <yong.wu@mediatek.com>
> > > ---
> > >  drivers/iommu/mtk_iommu.c | 41 +++++++++++++++++++++++++++++++++------
> > >  1 file changed, 35 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> > > index 6fe3ee2b2bf5..0e9c03cbab32 100644
> > > --- a/drivers/iommu/mtk_iommu.c
> > > +++ b/drivers/iommu/mtk_iommu.c
> > > @@ -184,6 +184,8 @@ static void mtk_iommu_tlb_flush_all(void *cookie)
> > >     struct mtk_iommu_data *data = cookie;
> > >
> > >     for_each_m4u(data) {
> > > +           if (!pm_runtime_active(data->dev))
> > > +                   continue;
> >
> > Is it guaranteed that the status is active in the check above, but then
> > the process is preempted and it goes down here?
> >
> > Shouldn't we do something like below?
> >
> >         ret = pm_runtime_get_if_active();
> >         if (!ret)
> >                 continue;
> >         if (ret < 0)
> >                 // handle error
> >
> >         // Flush
> >
> >         pm_runtime_put();
>
> Make sense. Thanks. There is a comment in arm_smmu.c "avoid touching
> dev->power.lock in fastpaths". To avoid this here too(we have many SoC
> don't have power-domain). then the code will be like:
>
>         bool has_pm = !!data->dev->pm_domain;
>
>         if (has_pm) {
>                 if (pm_runtime_get_if_in_use(data->dev) <= 0)
>                         continue;
>         }
>
>         xxxx
>
>         if (has_pm)
>                 pm_runtime_put(data->dev);

Looks good to me, thanks.

> >
> > Similar comment to the other places being changed by this patch.
> >
> > >             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);
> > > @@ -200,6 +202,10 @@ static void mtk_iommu_tlb_flush_range_sync(unsigned long iova, size_t size,
> > >     u32 tmp;
> > >
> > >     for_each_m4u(data) {
> > > +           /* skip tlb flush when pm is not active. */
> > > +           if (!pm_runtime_active(data->dev))
> > > +                   continue;
> > > +
> > >             spin_lock_irqsave(&data->tlb_lock, flags);
> > >             writel_relaxed(F_INVLD_EN1 | F_INVLD_EN0,
> > >                            data->base + data->plat_data->inv_sel_reg);
> [snip]
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