linux-kernel - Re: [PATCH v5 07/10] iommu/mediatek: Add REG_MMU_WR

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Message-ID: <5bd3bebc-54ab-b06a-e91b-50c1272ffbf0@gmail.com>
Date:   Wed, 1 Jul 2020 17:00:06 +0200
From:   Matthias Brugger <matthias.bgg@...il.com>
To:     chao hao <Chao.Hao@...iatek.com>
Cc:     Joerg Roedel <joro@...tes.org>, Rob Herring <robh+dt@...nel.org>,
        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 07/10] iommu/mediatek: Add REG_MMU_WR_LEN register
 definition



On 30/06/2020 12:59, chao hao wrote:
> On Mon, 2020-06-29 at 12:16 +0200, Matthias Brugger wrote:
>>
>> 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@...il.com>
>>> Signed-off-by: Chao Hao <chao.hao@...iatek.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?
>>
> 
> Thanks for your review carefully, we can name it to REG_MMU_WR_LEN_CTRL

Yes, that's mbetter, thanks.

> 
> 
>>> +#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? 
> 
> F_ is used to described some bits in register and doesn't have other
> meanings. The format is refer to other bits definition
> 
>> Also I think
>> it should be called '_MASK' instead of '_BIT' as it defines a mask of bits.
>>
> 
> Thanks for your advice.
> For F_MMU_WR_THROT_DIS_BIT:
> 1'b0: Enable write throttling mechanism
> 1'b1: Disable write throttling mechanism
> So I think we can name "F_MMU_WR_THROT_DIS  BIT(5) | BIT(21)" directly,
> it maybe more clearer.
> 

Is this what the datasheet names it? If not then I'd prefer F_MMU_WR_THROT_DIS_MASK.

Regards,
Matthias

>> 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 {
>>>
>