Re: [PATCH v4 12/24] iommu/mediatek: Move hw_init into attach_device

[Yong Wu]

On Thu, 2020-11-26 at 16:43 +0000, Robin Murphy wrote:
> On 2020-11-11 12:38, Yong Wu wrote:
> > In attach device, it will update the pagetable base address register.
> > Move the hw_init function also here. Then it only need call
> > pm_runtime_get/put one time here if m4u has power domain.
> 
> Doesn't that mean you'll end up writing most of the registers twice 
> every time? (first from mtk_iommu_resume(), then again from 
> mtk_iommu_hw_init())

I have skipped the first resume from mtk_iommu_resume with the code in
[15/24]:

@@ -828,6 +848,9 @@ static int __maybe_unused
mtk_iommu_runtime_resume(struct device *dev)

+/* Avoid first resume to affect the default value of registers below.*/
+if (!m4u_dom)
+   return 0;

> It might be neater to have mtk_iommu_hw_init() simply populate the 
> mtk_iommu_suspend_reg data with the initial values at probe time and 
> manually call mtk_iommu_resume() if the hardware is already powered up 
> at that point. Or maybe just don't bother saving those registers on 

Yes. All the power-domains are enabled in lk when bootup.

Actually I have plan to remove the pm_runtime_get in this attach_device
in the later patchset.

This is for fixing a issue that the screen is turned off when bootup.
In android project. we always show boot image. If iommu call
pm_runtime_get/put here, the display power-domain will be turned off
here given that iommu always probe before display drivers and iommu's
power-domain always is display's power-domain.

Even I plan to move the device's pm_runtime_enable into this
attach_device in the case all the drivers(iommu and display...) build as
modules. it is for skipping turn off display's power-domain in
genpd_power_off_unused.

This is only a plan, I'm not sure if power-domain could fix it like[1].

In this patchset, I'd like to keep current status.

[1]
https://patchwork.kernel.org/project/linux-clk/patch/20190630150230.7878-3-robdclark@xxxxxxxxx/

> suspend and put the initialisation directly in the resume path.
> 
> Robin.
> 
> > Signed-off-by: Yong Wu <yong.wu@xxxxxxxxxxxx>
> > ---
> >   drivers/iommu/mtk_iommu.c | 10 ++++++----
> >   1 file changed, 6 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> > index 55f9b329e637..cfdf5ce696fd 100644
> > --- a/drivers/iommu/mtk_iommu.c
> > +++ b/drivers/iommu/mtk_iommu.c
> > @@ -125,6 +125,8 @@ struct mtk_iommu_domain {
> >   
> >   static const struct iommu_ops mtk_iommu_ops;
> >   
> > +static int mtk_iommu_hw_init(const struct mtk_iommu_data *data);
> > +
> >   /*
> >    * In M4U 4GB mode, the physical address is remapped as below:
> >    *
> > @@ -380,12 +382,16 @@ static int mtk_iommu_attach_device(struct iommu_domain *domain,
> >   {
> >   	struct mtk_iommu_data *data = dev_iommu_priv_get(dev);
> >   	struct mtk_iommu_domain *dom = to_mtk_domain(domain);
> > +	int ret;
> >   
> >   	if (!data)
> >   		return -ENODEV;
> >   
> >   	/* Update the pgtable base address register of the M4U HW */
> >   	if (!data->m4u_dom) {
> > +		ret = mtk_iommu_hw_init(data);
> > +		if (ret)
> > +			return ret;
> >   		data->m4u_dom = dom;
> >   		writel(dom->cfg.arm_v7s_cfg.ttbr & MMU_PT_ADDR_MASK,
> >   		       data->base + REG_MMU_PT_BASE_ADDR);
> > @@ -729,10 +735,6 @@ static int mtk_iommu_probe(struct platform_device *pdev)
> >   
> >   	platform_set_drvdata(pdev, data);
> >   
> > -	ret = mtk_iommu_hw_init(data);
> > -	if (ret)
> > -		return ret;
> > -
> >   	ret = iommu_device_sysfs_add(&data->iommu, dev, NULL,
> >   				     "mtk-iommu.%pa", &ioaddr);
> >   	if (ret)
> >