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Subject: Re: [PATCH v4 6/7] iommu/mediatek: Add REG_MMU_WR_LEN definition
 preparing for mt6779
To:     chao hao <Chao.Hao@mediatek.com>
Cc:     Joerg Roedel <joro@8bytes.org>, Rob Herring <robh+dt@kernel.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,
        Yong Wu <yong.wu@mediatek.com>, FY Yang <fy.yang@mediatek.com>
References: <20200617030029.4082-1-chao.hao@mediatek.com>
 <20200617030029.4082-7-chao.hao@mediatek.com>
 <9e2c52d6-a887-1977-8877-fbcd30cb4261@gmail.com>
 <1592564184.5692.6.camel@mbjsdccf07>
From:   Matthias Brugger <matthias.bgg@gmail.com>
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Message-ID: <e9a62fd8-ed8c-05d6-1eaa-49d5a471cd3a@gmail.com>
Date:   Sun, 21 Jun 2020 13:01:27 +0200
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On 19/06/2020 12:56, chao hao wrote:
> On Wed, 2020-06-17 at 11:22 +0200, Matthias Brugger wrote:
>>
>> 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.
>>
> OK. thanks.
> We can use "has_wr_len" flag 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.
> 
> I will write description above to commit message in next version
> 
>>>
>>> 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)?
> 
> It doesn't have side effect. Becasue all the MTK platform have the
> register for iommu HW. If we need to have requirement for performance,
> we can set it by has_wr_len.
> But I'm Sorry, the name of flag(has_wr_len) is not exact, I will rename
> it in next version, ex: "wr_throt_en"
> 
>>
>>
>>>  	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.
> 
> Thanks for your advice.
> do you mean like this:
> struct plat_flag {
> 
>         #define  HAS_4GB_MODE   BIT(0)
>         #define  HAS_BCLK       BIT(1)
>         #define  REST_AXI       BIT(2)
>         ... ...
> 
>         u32 flag;
> };
> 
> struct mtk_iommu_plat_data {
>         ......
>         struct plat_flag flag;
>         ......
> };
> 

Nearly, I mean something like this:

#define  HAS_4GB_MODE   BIT(0)
#define  HAS_BCLK       BIT(1)
#define  REST_AXI       BIT(2)

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

struct mtk_iommu_plat_data {
	...
	u32 flags;
	...
}

if (MTK_IOMMU_HAS_FLAG(data->plat_data, HAS_BCLK)
...

Regards,
Matthias

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