Re: [PATCH v4 6/7] iommu/mediatek: Add REG_MMU_WR_LEN definition preparing for mt6779

[Matthias Brugger <matthias.bgg@gmail.com>]

On 17/06/2020 05:00, Chao Hao wrote:
> Some platforms(ex: mt6779) have a new register called by REG_MMU_WR_LEN
> to improve performance.
> This patch add this register definition.

Please be more specific what this register is about.

> 
> 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 a687e8db0e51..c706bca6487e 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
> +#define F_MMU_WR_THROT_DIS_BIT			(BIT(5) |  BIT(21))
>  
>  #define REG_MMU_CTRL_REG			0x110
>  #define F_MMU_TF_PROT_TO_PROGRAM_ADDR		(2 << 4)
> @@ -581,6 +583,12 @@ 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 (data->plat_data->has_wr_len) {
> +		/* 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);
> +	}
>  
>  	if (data->plat_data->reset_axi) {
>  		/* The register is called STANDARD_AXI_MODE in this case */
> @@ -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);

Can we read/write the register without any side effect although hardware has not
implemented it (!has_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 d51ff99c2c71..9971cedd72ea 100644
> --- a/drivers/iommu/mtk_iommu.h
> +++ b/drivers/iommu/mtk_iommu.h
> @@ -25,6 +25,7 @@ struct mtk_iommu_suspend_reg {
>  	u32				int_main_control;
>  	u32				ivrp_paddr;
>  	u32				vld_pa_rng;
> +	u32				wr_len;
>  };
>  
>  enum mtk_iommu_plat {
> @@ -43,6 +44,7 @@ struct mtk_iommu_plat_data {
>  	bool		    has_misc_ctrl;
>  	bool		    has_sub_comm;
>  	bool                has_vld_pa_rng;
> +	bool                has_wr_len;

Given the fact that we are adding more and more plat_data bool values, I think
it would make sense to use a u32 flags register and add the appropriate macro
definitions to set and check for a flag present.

Regards,
Matthias

>  	bool                reset_axi;
>  	u32                 inv_sel_reg;
>  	unsigned char       larbid_remap[8][4];
> 
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