linux-kernel - Re: [PATCH v9 3/3] iommu/mediatek: Allow page table PA up to 35bit

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Date:   Thu, 16 Jun 2022 15:52:46 +0800
From:   <yf.wang@...iatek.com>
To:     <robin.murphy@....com>
CC:     <Libo.Kang@...iatek.com>, <iommu@...ts.linux-foundation.org>,
        <joro@...tes.org>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>, <matthias.bgg@...il.com>,
        <miles.chen@...iatek.com>, <ning.li@...iatek.com>,
        <will@...nel.org>, <wsd_upstream@...iatek.com>,
        <yf.wang@...iatek.com>, <yong.wu@...iatek.com>
Subject: Re: [PATCH v9 3/3] iommu/mediatek: Allow page table PA up to 35bit

On Wed, 2022-06-15 at 18:25 +0100, Robin Murphy wrote:
> On 2022-06-15 17:12, yf.wang--- via iommu wrote:
> > From: Yunfei Wang <yf.wang@...iatek.com>
> > 
> > Single memory zone feature will remove ZONE_DMA32 and ZONE_DMA. So
> > add
> > the quirk IO_PGTABLE_QUIRK_ARM_MTK_TTBR_EXT to let level 1 and
> > level 2
> > pgtable support at most 35bit PA.
> 
> I'm not sure how this works in practice, given that you don't seem to
> be 
> setting the IOMMU's own DMA masks to more than 32 bits, so the DMA 
> mapping in io-pgtable is going to fail if you ever do actually
> allocate 
> a pagetable page above 4GB :/
> 

Hi Robin,
About DMA masks, the master device has set dma mask, when iommu do dma map,
it will check the dam_mask of the master dev to determine which range the
address of the iova alloc is in.

Add the quirk ARM_MTK_TTBR_EXT to let pgtable support larger phys memory.
Do actually test work fine, example:
pgtable phys address:0x12054006a, encoded to 32 bits ttbr:0x20540001


> > Signed-off-by: Ning Li <ning.li@...iatek.com>
> > Signed-off-by: Yunfei Wang <yf.wang@...iatek.com>
> > ---
> >   drivers/iommu/mtk_iommu.c | 14 +++++++++-----
> >   1 file changed, 9 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> > index 3d62399e8865..4dbc33758711 100644
> > --- a/drivers/iommu/mtk_iommu.c
> > +++ b/drivers/iommu/mtk_iommu.c
> > @@ -138,6 +138,7 @@
> >   /* PM and clock always on. e.g. infra iommu */
> >   #define PM_CLK_AO			BIT(15)
> >   #define IFA_IOMMU_PCIE_SUPPORT		BIT(16)
> > +#define PGTABLE_PA_35_EN		BIT(17)
> >   
> >   #define MTK_IOMMU_HAS_FLAG_MASK(pdata, _x, mask)	\
> >   				((((pdata)->flags) & (mask)) == (_x))
> > @@ -240,6 +241,7 @@ struct mtk_iommu_data {
> >   struct mtk_iommu_domain {
> >   	struct io_pgtable_cfg		cfg;
> >   	struct io_pgtable_ops		*iop;
> > +	u32				ttbr;
> >   
> >   	struct mtk_iommu_bank_data	*bank;
> >   	struct iommu_domain		domain;
> > @@ -596,6 +598,9 @@ static int mtk_iommu_domain_finalise(struct
> > mtk_iommu_domain *dom,
> >   		.iommu_dev = data->dev,
> >   	};
> >   
> > +	if (MTK_IOMMU_HAS_FLAG(data->plat_data, PGTABLE_PA_35_EN))
> > +		dom->cfg.quirks |= IO_PGTABLE_QUIRK_ARM_MTK_TTBR_EXT;
> > +
> >   	if (MTK_IOMMU_HAS_FLAG(data->plat_data, HAS_4GB_MODE))
> >   		dom->cfg.oas = data->enable_4GB ? 33 : 32;
> >   	else
> > @@ -684,8 +689,8 @@ static int mtk_iommu_attach_device(struct
> > iommu_domain *domain,
> >   			goto err_unlock;
> >   		}
> >   		bank->m4u_dom = dom;
> > -		writel(dom->cfg.arm_v7s_cfg.ttbr & MMU_PT_ADDR_MASK,
> > -		       bank->base + REG_MMU_PT_BASE_ADDR);
> > +		bank->m4u_dom->ttbr = MTK_IOMMU_ADDR(dom-
> > >cfg.arm_v7s_cfg.ttbr);
> > +		writel(bank->m4u_dom->ttbr, data->base +
> > REG_MMU_PT_BASE_ADDR);
> 
> To add to my comment on patch #1, having to make this change here 
> further indicates that you're using it the wrong way.
> 
> Thanks,
> Robin.
> 

Hi Robin,
According to your Path#1's suggestion, next version will keep ttbr to encoded 32 bits,
then will don't need to modify it.

Thanks,
Yunfei.