Re: [PATCH] iommu/qcom: add optional clock for TLB invalidate

[Shawn Guo <shawn.guo@linaro.org>]

Hi Bjorn,

On Mon, May 11, 2020 at 10:52:42PM -0700, Bjorn Andersson wrote:
> On Sat 09 May 06:08 PDT 2020, Shawn Guo wrote:
> 
> > On some SoCs like MSM8939 with A405 adreno, there is a gfx_tbu clock
> > needs to be on while doing TLB invalidate. Otherwise, TLBSYNC status
> > will not be correctly reflected, causing the system to go into a bad
> > state.  Add it as an optional clock, so that platforms that have this
> > clock can pass it over DT.
> > 
> > Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
> > ---
> >  drivers/iommu/qcom_iommu.c | 16 ++++++++++++++++
> >  1 file changed, 16 insertions(+)
> > 
> > diff --git a/drivers/iommu/qcom_iommu.c b/drivers/iommu/qcom_iommu.c
> > index 0e2a96467767..2f6c6da7d540 100644
> > --- a/drivers/iommu/qcom_iommu.c
> > +++ b/drivers/iommu/qcom_iommu.c
> > @@ -45,6 +45,7 @@ struct qcom_iommu_dev {
> >  	struct device		*dev;
> >  	struct clk		*iface_clk;
> >  	struct clk		*bus_clk;
> > +	struct clk		*tlb_clk;
> >  	void __iomem		*local_base;
> >  	u32			 sec_id;
> >  	u8			 num_ctxs;
> > @@ -643,11 +644,20 @@ static int qcom_iommu_enable_clocks(struct qcom_iommu_dev *qcom_iommu)
> >  		return ret;
> >  	}
> >  
> > +	ret = clk_prepare_enable(qcom_iommu->tlb_clk);
> > +	if (ret) {
> > +		dev_err(qcom_iommu->dev, "Couldn't enable tlb_clk\n");
> > +		clk_disable_unprepare(qcom_iommu->bus_clk);
> > +		clk_disable_unprepare(qcom_iommu->iface_clk);
> > +		return ret;
> > +	}
> 
> Seems this is an excellent opportunity to replace
> qcom_iommu_enable_clocks() to clk_bulk_prepare_enable() and disable,
> respectively.

So we have two required and one optional clocks.  I guess we don't want
to use clk_bulk_get_optional() to get all of them as optional.  So we
will end up with getting clock with individual call and enabling/disabling
with bulk version.  I'm personally not fond of this mixed style.  But if
you really like this, I can change.

> 
> > +
> >  	return 0;
> >  }
> >  
> >  static void qcom_iommu_disable_clocks(struct qcom_iommu_dev *qcom_iommu)
> >  {
> > +	clk_disable_unprepare(qcom_iommu->tlb_clk);
> >  	clk_disable_unprepare(qcom_iommu->bus_clk);
> >  	clk_disable_unprepare(qcom_iommu->iface_clk);
> >  }
> > @@ -839,6 +849,12 @@ static int qcom_iommu_device_probe(struct platform_device *pdev)
> >  		return PTR_ERR(qcom_iommu->bus_clk);
> >  	}
> >  
> > +	qcom_iommu->tlb_clk = devm_clk_get(dev, "tlb");
> 
> Wouldn't "tbu" be a better name for this clock? Given that seems the
> actually be the hardware block you're clocking.

I was trying to emphasize the function of this clock.  But I agree that
'tbu' is a better name now.  I will change it in v2.

Thanks for the comments.

Shawn
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