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SubjectRe: [PATCH v5 04/10] iommu/mediatek: Setting MISC_CTRL register
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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@gmail.com>
> Suggested-by: Yong Wu <yong.wu@mediatek.com>
> Signed-off-by: Chao Hao <chao.hao@mediatek.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))
>

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