Re: [PATCH v5 07/10] iommu/mediatek: Add REG_MMU_WR_LEN register definition

[chao hao]

On Mon, 2020-06-29 at 12:16 +0200, Matthias Brugger wrote:
> 
> On 29/06/2020 09:13, Chao Hao wrote:
> > Some platforms(ex: mt6779) need to improve performance by setting
> > REG_MMU_WR_LEN register. And we can use WR_THROT_EN macro to control
> > whether we need to set the register. If the register uses default value,
> > iommu will send command to EMI without restriction, when the number of
> > commands become more and more, it will drop the EMI performance. So when
> > more than ten_commands(default value) don't be handled for EMI, iommu will
> > stop send command to EMI for keeping EMI's performace by enabling write
> > throttling mechanism(bit[5][21]=0) in MMU_WR_LEN_CTRL register.
> > 
> > Cc: Matthias Brugger <matthias.bgg@xxxxxxxxx>
> > Signed-off-by: Chao Hao <chao.hao@xxxxxxxxxxxx>
> > ---
> >  drivers/iommu/mtk_iommu.c | 10 ++++++++++
> >  drivers/iommu/mtk_iommu.h |  2 ++
> >  2 files changed, 12 insertions(+)
> > 
> > diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> > index ec1f86913739..92316c4175a9 100644
> > --- a/drivers/iommu/mtk_iommu.c
> > +++ b/drivers/iommu/mtk_iommu.c
> > @@ -46,6 +46,8 @@
> >  #define F_MMU_STANDARD_AXI_MODE_BIT		(BIT(3) | BIT(19))
> >  
> >  #define REG_MMU_DCM_DIS				0x050
> > +#define REG_MMU_WR_LEN				0x054
> 
> The register name is confusing. For me it seems to describe the length of a
> write but it is used for controlling the write throttling. Is this the name
> that's used in the datasheet?
> 

Thanks for your review carefully, we can name it to REG_MMU_WR_LEN_CTRL


> > +#define F_MMU_WR_THROT_DIS_BIT			(BIT(5) |  BIT(21))
> 
> There are two spaces between '|' and 'BIT(21)', should be one.
> 
> Regarding the name of the define, what does the 'F_' statnds for? 

F_ is used to described some bits in register and doesn't have other
meanings. The format is refer to other bits definition

> Also I think
> it should be called '_MASK' instead of '_BIT' as it defines a mask of bits.
> 

Thanks for your advice.
For F_MMU_WR_THROT_DIS_BIT:
1'b0: Enable write throttling mechanism
1'b1: Disable write throttling mechanism
So I think we can name "F_MMU_WR_THROT_DIS  BIT(5) | BIT(21)" directly,
it maybe more clearer.

> Regards,
> Matthias
> 
> >  
> >  #define REG_MMU_CTRL_REG			0x110
> >  #define F_MMU_TF_PROT_TO_PROGRAM_ADDR		(2 << 4)
> > @@ -582,6 +584,12 @@ static int mtk_iommu_hw_init(const struct mtk_iommu_data *data)
> >  		writel_relaxed(regval, data->base + REG_MMU_VLD_PA_RNG);
> >  	}
> >  	writel_relaxed(0, data->base + REG_MMU_DCM_DIS);
> > +	if (MTK_IOMMU_HAS_FLAG(data->plat_data, WR_THROT_EN)) {
> > +		/* write command throttling mode */
> > +		regval = readl_relaxed(data->base + REG_MMU_WR_LEN);
> > +		regval &= ~F_MMU_WR_THROT_DIS_BIT;
> > +		writel_relaxed(regval, data->base + REG_MMU_WR_LEN);
> > +	}
> >  
> >  	regval = readl_relaxed(data->base + REG_MMU_MISC_CTRL);
> >  	if (MTK_IOMMU_HAS_FLAG(data->plat_data, RESET_AXI)) {
> > @@ -737,6 +745,7 @@ static int __maybe_unused mtk_iommu_suspend(struct device *dev)
> >  	struct mtk_iommu_suspend_reg *reg = &data->reg;
> >  	void __iomem *base = data->base;
> >  
> > +	reg->wr_len = readl_relaxed(base + REG_MMU_WR_LEN);
> >  	reg->misc_ctrl = readl_relaxed(base + REG_MMU_MISC_CTRL);
> >  	reg->dcm_dis = readl_relaxed(base + REG_MMU_DCM_DIS);
> >  	reg->ctrl_reg = readl_relaxed(base + REG_MMU_CTRL_REG);
> > @@ -761,6 +770,7 @@ static int __maybe_unused mtk_iommu_resume(struct device *dev)
> >  		dev_err(data->dev, "Failed to enable clk(%d) in resume\n", ret);
> >  		return ret;
> >  	}
> > +	writel_relaxed(reg->wr_len, base + REG_MMU_WR_LEN);
> >  	writel_relaxed(reg->misc_ctrl, base + REG_MMU_MISC_CTRL);
> >  	writel_relaxed(reg->dcm_dis, base + REG_MMU_DCM_DIS);
> >  	writel_relaxed(reg->ctrl_reg, base + REG_MMU_CTRL_REG);
> > diff --git a/drivers/iommu/mtk_iommu.h b/drivers/iommu/mtk_iommu.h
> > index be6d32ee5bda..ce4f4e8f03aa 100644
> > --- a/drivers/iommu/mtk_iommu.h
> > +++ b/drivers/iommu/mtk_iommu.h
> > @@ -24,6 +24,7 @@
> >  #define RESET_AXI			BIT(3)
> >  #define OUT_ORDER_EN			BIT(4)
> >  #define HAS_SUB_COMM			BIT(5)
> > +#define WR_THROT_EN			BIT(6)
> >  
> >  #define MTK_IOMMU_HAS_FLAG(pdata, _x) \
> >  		((((pdata)->flags) & (_x)) == (_x))
> > @@ -36,6 +37,7 @@ struct mtk_iommu_suspend_reg {
> >  	u32				int_main_control;
> >  	u32				ivrp_paddr;
> >  	u32				vld_pa_rng;
> > +	u32				wr_len;
> >  };
> >  
> >  enum mtk_iommu_plat {
> >