linux-kernel - Re: [PATCH v5 04/10] iommu/mediatek: Setting MISC

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Date:   Mon, 29 Jun 2020 11:28:11 +0200
From:   Matthias Brugger <matthias.bgg@...il.com>
To:     Chao Hao <chao.hao@...iatek.com>, Joerg Roedel <joro@...tes.org>,
        Rob Herring <robh+dt@...nel.org>
Cc:     Yong Wu <yong.wu@...iatek.com>, Evan Green <evgreen@...omium.org>,
        iommu@...ts.linux-foundation.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, wsd_upstream@...iatek.com,
        FY Yang <fy.yang@...iatek.com>
Subject: Re: [PATCH v5 04/10] iommu/mediatek: Setting MISC_CTRL register



On 29/06/2020 09:13, Chao Hao wrote:
> Add F_MMU_IN_ORDER_WR_EN and F_MMU_STANDARD_AXI_MODE_BIT definition
> in MISC_CTRL register.
> F_MMU_STANDARD_AXI_MODE_BIT:
>   If we set F_MMU_STANDARD_AXI_MODE_BIT(bit[3][19] = 0, not follow
> standard AXI protocol), iommu will send urgent read command firstly
> compare with normal read command to improve performance.

Can you please help me to understand the phrase. Sorry I'm not a AXI specialist.
Does this mean that you will send a 'urgent read command' which is not described
in the specifications instead of a normal read command?

> F_MMU_IN_ORDER_WR_EN:
>   If we set F_MMU_IN_ORDER_WR_EN(bit[1][17] = 0, out-of-order write), iommu
> will re-order write command and send more higher priority write command
> instead of sending write command in order. The feature be controlled
> by OUT_ORDER_EN macro definition.
> 
> Cc: Matthias Brugger <matthias.bgg@...il.com>
> Suggested-by: Yong Wu <yong.wu@...iatek.com>
> Signed-off-by: Chao Hao <chao.hao@...iatek.com>
> ---
>  drivers/iommu/mtk_iommu.c | 12 +++++++++++-
>  drivers/iommu/mtk_iommu.h |  1 +
>  2 files changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> index 8f81df6cbe51..67b46b5d83d9 100644
> --- a/drivers/iommu/mtk_iommu.c
> +++ b/drivers/iommu/mtk_iommu.c
> @@ -42,6 +42,9 @@
>  #define F_INVLD_EN1				BIT(1)
>  
>  #define REG_MMU_MISC_CTRL			0x048
> +#define F_MMU_IN_ORDER_WR_EN			(BIT(1) | BIT(17))
> +#define F_MMU_STANDARD_AXI_MODE_BIT		(BIT(3) | BIT(19))

Wouldn't it make more sense to name it F_MMU_STANDARD_AXI_MODE_EN?

> +
>  #define REG_MMU_DCM_DIS				0x050
>  
>  #define REG_MMU_CTRL_REG			0x110
> @@ -574,10 +577,17 @@ static int mtk_iommu_hw_init(const struct mtk_iommu_data *data)
>  	}
>  	writel_relaxed(0, data->base + REG_MMU_DCM_DIS);
>  
> +	regval = readl_relaxed(data->base + REG_MMU_MISC_CTRL);

We only need to read regval in the else branch.

>  	if (MTK_IOMMU_HAS_FLAG(data->plat_data, RESET_AXI)) {
>  		/* The register is called STANDARD_AXI_MODE in this case */
> -		writel_relaxed(0, data->base + REG_MMU_MISC_CTRL);
> +		regval = 0;
> +	} else {
> +		/* For mm_iommu, it can improve performance by the setting */
> +		regval &= ~F_MMU_STANDARD_AXI_MODE_BIT;
> +		if (MTK_IOMMU_HAS_FLAG(data->plat_data, OUT_ORDER_EN))
> +			regval &= ~F_MMU_IN_ORDER_WR_EN;
>  	}
> +	writel_relaxed(regval, data->base + REG_MMU_MISC_CTRL);
>  
>  	if (devm_request_irq(data->dev, data->irq, mtk_iommu_isr, 0,
>  			     dev_name(data->dev), (void *)data)) {
> diff --git a/drivers/iommu/mtk_iommu.h b/drivers/iommu/mtk_iommu.h
> index 7cc39f729263..4b780b651ef4 100644
> --- a/drivers/iommu/mtk_iommu.h
> +++ b/drivers/iommu/mtk_iommu.h
> @@ -22,6 +22,7 @@
>  #define HAS_BCLK			BIT(1)
>  #define HAS_VLD_PA_RNG			BIT(2)
>  #define RESET_AXI			BIT(3)
> +#define OUT_ORDER_EN			BIT(4)

Maybe something like OUT_ORDER_WR_EN, to make clear that it's about the the
write path.

>  
>  #define MTK_IOMMU_HAS_FLAG(pdata, _x) \
>  		((((pdata)->flags) & (_x)) == (_x))
>