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SubjectRe: [PATCH v9 08/21] iommu/io-pgtable-arm-v7s: Extend MediaTek 4GB Mode
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On Wed, 2019-08-14 at 15:41 +0100, Will Deacon wrote:
> Hi Yong Wu,
>
> Sorry, but I'm still deeply confused by this patch.

Sorry for this. the "4GB mode" really is a bit odd...

>
> On Sat, Aug 10, 2019 at 03:58:08PM +0800, Yong Wu wrote:
> > MediaTek extend the arm v7s descriptor to support the dram over 4GB.
> >
> > In the mt2712 and mt8173, it's called "4GB mode", the physical address
> > is from 0x4000_0000 to 0x1_3fff_ffff, but from EMI point of view, it
> > is remapped to high address from 0x1_0000_0000 to 0x1_ffff_ffff, the
> > bit32 is always enabled. thus, in the M4U, we always enable the bit9
> > for all PTEs which means to enable bit32 of physical address. Here is
> > the detailed remap relationship in the "4GB mode":
> > CPU PA -> HW PA
> > 0x4000_0000 0x1_4000_0000 (Add bit32)
> > 0x8000_0000 0x1_8000_0000 ...
> > 0xc000_0000 0x1_c000_0000 ...
> > 0x1_0000_0000 0x1_0000_0000 (No change)
>
> So in this example, there are no PAs below 0x4000_0000 yet you later
> add code to deal with that:
>
> > + /* Workaround for MTK 4GB Mode: Add BIT32 only when PA < 0x4000_0000.*/
> > + if (cfg->oas == ARM_V7S_MTK_4GB_OAS && paddr < 0x40000000UL)
> > + paddr |= BIT_ULL(32);
>
> Why? Mainline currently doesn't do anything like this for the "4gb mode"
> support as far as I can tell. In fact, we currently unconditionally set
> bit 32 in the physical address returned by iova_to_phys() which wouldn't
> match your CPU PAs listed above, so I'm confused about how this is supposed
> to work.

Actually current mainline have a bug for this. So I tried to use another
special patch[1] for it in v8.

But the issue is not critical since MediaTek multimedia consumer(v4l2
and drm) don't call iommu_iova_to_phys currently.

>
> The way I would like this quirk to work is that the io-pgtable code
> basically sets bit 9 in the pte when bit 32 is set in the physical address,
> and sets bit 4 in the pte when bit 33 is set in the physical address. It
> would then do the opposite when converting a pte to a physical address.
>
> That way, your driver can call the page table code directly with the high
> addresses and we don't have to do any manual offsetting or range checking
> in the page table code.

In this case, the mt8183 can work successfully while the "4gb
mode"(mt8173/mt2712) can not.

In the "4gb mode", As the remap relationship above, we should always add
bit32 in pte as we did in [2]. and need add bit32 in the
"iova_to_phys"(Not always add.). That means the "4gb mode" has a special
flow:
a. Always add bit32 in paddr_to_iopte.
b. Add bit32 only when PA < 0x40000000 in iopte_to_paddr.

>
> Please can you explain to me why the diff below doesn't work on top of
> this series?

The diff below is just I did in v8[3]. The different is that I move the
"4gb mode" special flow in the mtk_iommu.c in v8, the code is like
[4]below. When I sent v9, I found that I can distinguish the "4gb mode"
with "oas == 33" in v7s. then I can "simply" add the 4gb special flow[5]
based on your diff.


> I'm happy to chat on IRC if you think it would be easier,
> because I have a horrible feeling that we've been talking past each other
> and I'd like to see this support merged for 5.4.

Thanks very much for your view, I'm sorry that I don't have IRC. I will
send the next version quickly if we have a conclusion here. Then Which
way is better? If you'd like keep the pagetable code clean, I will add
the "4gb mode" special flow into mtk_iommu.c.

Thanks.


[1]http://lists.infradead.org/pipermail/linux-mediatek/2019-June/020988.html
[2]
https://elixir.bootlin.com/linux/v5.3-rc4/source/drivers/iommu/io-pgtable-arm-v7s.c#L299
[3]http://lists.infradead.org/pipermail/linux-mediatek/2019-June/020991.html

[4]======4gb mode special flow in mtk_iommu.c======================

+#define MTK_IOMMU_4GB_MODE_REMAP_BASE 0x140000000UL

@@ -380,12 +379,16 @@ static int mtk_iommu_map(struct iommu_domain
*domain, unsigned long iova,
phys_addr_t paddr, size_t size, int prot)
{
struct mtk_iommu_domain *dom = to_mtk_domain(domain);
+ struct mtk_iommu_data *data = mtk_iommu_get_m4u_data();
unsigned long flags;
int ret;

+ /* The "4GB mode" M4U physically can not use the lower remap of Dram.
*/
+ if (data->enable_4GB)
+ paddr |= BIT_ULL(32);
+
spin_lock_irqsave(&dom->pgtlock, flags);
- ret = dom->iop->map(dom->iop, iova, paddr & DMA_BIT_MASK(32),
- size, prot);
+ ret = dom->iop->map(dom->iop, iova, paddr, size, prot);
spin_unlock_irqrestore(&dom->pgtlock, flags);

return ret;
@@ -422,8 +425,8 @@ static phys_addr_t mtk_iommu_iova_to_phys(struct
iommu_domain *domain,
pa = dom->iop->iova_to_phys(dom->iop, iova);
spin_unlock_irqrestore(&dom->pgtlock, flags);

- if (data->enable_4GB && pa < MTK_IOMMU_4GB_MODE_REMAP_BASE)
- pa |= BIT_ULL(32);
+ if (data->enable_4GB && pa >= MTK_IOMMU_4GB_MODE_REMAP_BASE)
+ pa &= ~BIT_ULL(32);

return pa;
}
=============================================================
[5]:
=========================================================
diff --git a/drivers/iommu/io-pgtable-arm-v7s.c
b/drivers/iommu/io-pgtable-arm-v7s.c
index 78fd11e..8e974a5 100644
--- a/drivers/iommu/io-pgtable-arm-v7s.c
+++ b/drivers/iommu/io-pgtable-arm-v7s.c
@@ -184,7 +184,7 @@ static arm_v7s_iopte paddr_to_iopte(phys_addr_t
paddr, int lvl,
arm_v7s_iopte pte = paddr & ARM_V7S_LVL_MASK(lvl);

if (cfg->quirks & IO_PGTABLE_QUIRK_ARM_MTK_4GB) {
- if (paddr & BIT_ULL(32))
+ if (paddr & BIT_ULL(32) || cfg->oas == 33)
pte |= ARM_V7S_ATTR_MTK_PA_BIT32;
if (paddr & BIT_ULL(33))
pte |= ARM_V7S_ATTR_MTK_PA_BIT33;
@@ -207,7 +207,9 @@ static phys_addr_t iopte_to_paddr(arm_v7s_iopte pte,
int lvl,

paddr = pte & mask;
if (cfg->quirks & IO_PGTABLE_QUIRK_ARM_MTK_4GB) {
- if (pte & ARM_V7S_ATTR_MTK_PA_BIT32)
+ if (cfg->oas == 33 && paddr < 0x40000000UL)
+ paddr |= BIT_ULL(32);
+ else if (pte & ARM_V7S_ATTR_MTK_PA_BIT32)
paddr |= BIT_ULL(32);
if (pte & ARM_V7S_ATTR_MTK_PA_BIT33)
paddr |= BIT_ULL(33);
============================================================
>
> Will
>
> --->8
>
> diff --git a/drivers/iommu/io-pgtable-arm-v7s.c b/drivers/iommu/io-pgtable-arm-v7s.c
> index ab12ef5f8b03..d8d84617c822 100644
> --- a/drivers/iommu/io-pgtable-arm-v7s.c
> +++ b/drivers/iommu/io-pgtable-arm-v7s.c
> @@ -184,7 +184,7 @@ static arm_v7s_iopte paddr_to_iopte(phys_addr_t paddr, int lvl,
> arm_v7s_iopte pte = paddr & ARM_V7S_LVL_MASK(lvl);
>
> if (cfg->quirks & IO_PGTABLE_QUIRK_ARM_MTK_EXT) {
> - if ((paddr & BIT_ULL(32)) || cfg->oas == ARM_V7S_MTK_4GB_OAS)
> + if (paddr & BIT_ULL(32))
> pte |= ARM_V7S_ATTR_MTK_PA_BIT32;
> if (paddr & BIT_ULL(33))
> pte |= ARM_V7S_ATTR_MTK_PA_BIT33;
> @@ -206,17 +206,14 @@ static phys_addr_t iopte_to_paddr(arm_v7s_iopte pte, int lvl,
> mask = ARM_V7S_LVL_MASK(lvl);
>
> paddr = pte & mask;
> - if (cfg->oas == 32 || !(cfg->quirks & IO_PGTABLE_QUIRK_ARM_MTK_EXT))
> - return paddr;
>
> - if (pte & ARM_V7S_ATTR_MTK_PA_BIT33)
> - paddr |= BIT_ULL(33);
> + if (cfg->quirks & IO_PGTABLE_QUIRK_ARM_MTK_EXT) {
> + if (pte & ARM_V7S_ATTR_MTK_PA_BIT32)
> + paddr |= BIT_ULL(32);
> + if (pte & ARM_V7S_ATTR_MTK_PA_BIT33)
> + paddr |= BIT_ULL(33);
> + }
>
> - /* Workaround for MTK 4GB Mode: Add BIT32 only when PA < 0x4000_0000.*/
> - if (cfg->oas == ARM_V7S_MTK_4GB_OAS && paddr < 0x40000000UL)
> - paddr |= BIT_ULL(32);
> - else if (pte & ARM_V7S_ATTR_MTK_PA_BIT32)
> - paddr |= BIT_ULL(32);
> return paddr;
> }
>
> diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> index d5b9454352fd..3ae54dedede0 100644
> --- a/drivers/iommu/mtk_iommu.c
> +++ b/drivers/iommu/mtk_iommu.c
> @@ -286,7 +286,7 @@ static int mtk_iommu_domain_finalise(struct mtk_iommu_domain *dom)
> if (!IS_ENABLED(CONFIG_PHYS_ADDR_T_64BIT))
> dom->cfg.oas = 32;
> else if (data->enable_4GB)
> - dom->cfg.oas = ARM_V7S_MTK_4GB_OAS;
> + dom->cfg.oas = 33;
> else
> dom->cfg.oas = 34;
>
> diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h
> index 27337395bd42..a2a52c349fe4 100644
> --- a/include/linux/io-pgtable.h
> +++ b/include/linux/io-pgtable.h
> @@ -113,8 +113,6 @@ struct io_pgtable_cfg {
> };
> };
>
> -#define ARM_V7S_MTK_4GB_OAS 33
> -
> /**
> * struct io_pgtable_ops - Page table manipulation API for IOMMU drivers.
> *


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