Re: [PATCH v5 04/10] iommu/mediatek: Setting MISC_CTRL register

[chao hao]

On Wed, 2020-07-01 at 16:58 +0200, Matthias Brugger wrote:
> 
> 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.
> 
ok, thanks

> >>
> >>> 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@xxxxxxxxx>
> >>> Suggested-by: Yong Wu <yong.wu@xxxxxxxxxxxx>
> >>> Signed-off-by: Chao Hao <chao.hao@xxxxxxxxxxxx>
> >>> ---
> >>>  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.
> 

ok, thanks for your advice

> 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))
> >>>
> >