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

[Yong Wu]

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@xxxxxxxxxxxx>
> > ---
> >  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);
> 
> 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]