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Subject: Re: [PATCH v5 04/10] iommu/mediatek: Setting MISC_CTRL register
To:     chao hao <Chao.Hao@mediatek.com>
Cc:     Joerg Roedel <joro@8bytes.org>, Rob Herring <robh+dt@kernel.org>,
        Yong Wu <yong.wu@mediatek.com>,
        Evan Green <evgreen@chromium.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,
        FY Yang <fy.yang@mediatek.com>
References: <20200629071310.1557-1-chao.hao@mediatek.com>
 <20200629071310.1557-5-chao.hao@mediatek.com>
 <0e9ceba8-0cc4-44a1-148c-1c9a6b3844ce@gmail.com>
 <1593514398.2581.7.camel@mbjsdccf07>
From:   Matthias Brugger <matthias.bgg@gmail.com>
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Date:   Wed, 1 Jul 2020 16:58:27 +0200
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On 30/06/2020 12:53, chao hao wrote:
> On Mon, 2020-06-29 at 11:28 +0200, Matthias Brugger wrote:
>>
>> 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?
> 
> ok.
> iommu sends read command to next bus_node normally(we can name it to
> cmd1), when cmd1 isn't handled by next bus_node, iommu has a urgent read
> command is needed to be sent(we can name it to cmd2), iommu will send
> cmd2 and replace cmd1. So cmd2 is handled by next bus_node firstly and
> cmd2 will be handled secondly.
> But for standard AXI protocol, it will ignore the priority of read
> command and only be handled in order. So cmd2 is handled by next
> bus_node after cmd1 is done.
> 

Thanks. So I propose change this part of the commit message to something like:
F_MMU_STANDARD_AXI_MODE_BIT:
If we set F_MMU_STANDARD_AXI_MODE_EN_MASK (bit[3][19] = 0, not follow standard
AXI protocol), the iommu will priorize sending of urgent read command over a
normal read command. This improves the performance.

>>
>>> 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.

F_MMU_IN_ORDER_WR_EN:
If we set F_MMU_IN_ORDER_WR_EN_MASK (bit[1][17] = 0, out-of-order write), the
iommu will re-order write commands and send the write command with higher
priority. Otherwise the sending of write commands will be done in order. The
feature is controlled by OUT_ORDER_WR_EN platform data flag.


>>>
>>> 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?
> ok, you are right.
> 1'b1: follow standard axi protocol
> 

What about
F_MMU_IN_ORDER_WR_EN_MASK
F_MMU_STANDARD_AXI_MODE_EN_MASK

Background is that we have to set/unset two bits to enable or disable the
feature, so it's a mask we have to apply to the register.

Regards,
Matthias

>>
>>> +
>>>  #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.
> 
> ok, I got it. thanks
> 
>>
>>>  	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.
>>
> ok, thanks for your advice.
> 
>>>  
>>>  #define MTK_IOMMU_HAS_FLAG(pdata, _x) \
>>>  		((((pdata)->flags) & (_x)) == (_x))
>>>
>