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Subject: Re: [PATCH v5 07/10] iommu/mediatek: Add REG_MMU_WR_LEN register
 definition
To:     Chao Hao <chao.hao@mediatek.com>, Joerg Roedel <joro@8bytes.org>,
        Rob Herring <robh+dt@kernel.org>
Cc:     Yong Wu <yong.wu@mediatek.com>, Evan Green <evgreen@chromium.org>,
        iommu@lists.linux-foundation.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, wsd_upstream@mediatek.com,
        FY Yang <fy.yang@mediatek.com>
References: <20200629071310.1557-1-chao.hao@mediatek.com>
 <20200629071310.1557-8-chao.hao@mediatek.com>
From:   Matthias Brugger <matthias.bgg@gmail.com>
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Message-ID: <ccb63946-e187-187e-c92c-0423f1831d8f@gmail.com>
Date:   Mon, 29 Jun 2020 12:16:42 +0200
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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@gmail.com>
> Signed-off-by: Chao Hao <chao.hao@mediatek.com>
> ---
>  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?

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

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 {
>