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

[Yong Wu]

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)'
> 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@xxxxxxxxxxxx>
> > ---
> >   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.
> > +	 */
> >   	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
> >