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Subject: Re: [PATCH v6 06/20] iommu/io-pgtable-arm-v7s: Extend MediaTek 4GB
 Mode
From:   Yong Wu <yong.wu@mediatek.com>
To:     Evan Green <evgreen@chromium.org>
CC:     Joerg Roedel <joro@8bytes.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Rob Herring <robh+dt@kernel.org>,
        Tomasz Figa <tfiga@google.com>,
        Will Deacon <will.deacon@arm.com>,
        <linux-mediatek@lists.infradead.org>,
        <srv_heupstream@mediatek.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <iommu@lists.linux-foundation.org>, Arnd Bergmann <arnd@arndb.de>,
        <yingjoe.chen@mediatek.com>, <youlin.pei@mediatek.com>,
        Nicolas Boichat <drinkcat@chromium.org>
Date:   Fri, 1 Feb 2019 17:42:28 +0800
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On Thu, 2019-01-31 at 11:23 -0800, Evan Green wrote:
> On Wed, Jan 30, 2019 at 10:59 PM Yong Wu <yong.wu@mediatek.com> wrote:
> >
> > On Wed, 2019-01-30 at 10:28 -0800, Evan Green wrote:
> > > On Mon, Dec 31, 2018 at 7:57 PM Yong Wu <yong.wu@mediatek.com> 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.
> > >
> > > I got a little lost here. I get that you're trying to explain why you
> > > always used to set bit32 of the physical address. But I don't totally
> > > get the part about physical addresses being from 0x4000_0000 -
> > > 0x1_3fff_ffff, but also from 0x1_0000_0000-0x1_ffff_ffff. Are you
> > > saying that the physical addresses from the iommu's perspective were
> > > always >0x1_0000_0000?
> >
> > Yes. From the IOMMU's perspective, the Physical address is from
> > 0x1_0000_0000 to 0x1_ffff_ffff.
> >
> > > But then from whose perspective is it 0x4000_0000? ...
> >
> > I guess from SW point view. it is from 0x4000_0000 to 0x1_3fff_ffff.
> >
> > If 4GB mode is enabled, the memory property in dts like this:
> >
> >         memory@40000000 {
> >                 device_type = "memory";
> >                 reg = <0 0x40000000 0x00000001 0x00000000>;
> >         };
> >
> > > oh, or you're saying there was some sort of remapping
> > > facility that moved the physical addresses around?
> > >
> > > >
> > > > but in mt8183, M4U support the dram from 0x4000_0000 to 0x3_ffff_ffff
> > > > which isn't remaped. We extend the PTEs: the bit9 represent bit32 of
> > > > PA and the bit4 represent bit33 of PA. Meanwhile the iova still is
> > > > 32bits.
> > > >
> > > > In order to unify code, in the "4GB mode", we add the bit32 for the
> > > > physical address manually in our driver.
> > > >
> > > > Correspondingly, Adding bit32 and bit33 for the PA in the iova_to_phys
> > > > has to been moved into v7s.
> > > >
> > > > Regarding whether the pagetable address could be over 4GB, the mt8183
> > > > support it while the previous mt8173 don't. thus keep it as is.
> > > >
> > > > Signed-off-by: Yong Wu <yong.wu@mediatek.com>
> > > > Reviewed-by: Robin Murphy <robin.murphy@arm.com>
> > > > ---
> > > >  drivers/iommu/io-pgtable-arm-v7s.c | 31 ++++++++++++++++++++++++-------
> > > >  drivers/iommu/io-pgtable.h         |  7 +++----
> > > >  drivers/iommu/mtk_iommu.c          | 14 ++++++++------
> > > >  drivers/iommu/mtk_iommu.h          |  1 +
> > > >  4 files changed, 36 insertions(+), 17 deletions(-)
> > > >
> > > > diff --git a/drivers/iommu/io-pgtable-arm-v7s.c b/drivers/iommu/io-pgtable-arm-v7s.c
> > > > index 11d8505..8803a35 100644
> > > > --- a/drivers/iommu/io-pgtable-arm-v7s.c
> > > > +++ b/drivers/iommu/io-pgtable-arm-v7s.c
> > > > @@ -124,7 +124,9 @@
> > > >  #define ARM_V7S_TEX_MASK               0x7
> > > >  #define ARM_V7S_ATTR_TEX(val)          (((val) & ARM_V7S_TEX_MASK) << ARM_V7S_TEX_SHIFT)
> > > >
> > > > -#define ARM_V7S_ATTR_MTK_4GB           BIT(9) /* MTK extend it for 4GB mode */
> > > > +/* MediaTek extend the two bits below for over 4GB mode */
> > > > +#define ARM_V7S_ATTR_MTK_PA_BIT32      BIT(9)
> > > > +#define ARM_V7S_ATTR_MTK_PA_BIT33      BIT(4)
> > >
> > > If other vendors start doing stuff like this we'll need a more generic
> > > way to handle this... but I guess until we see a pattern this is okay.
> > >
> > > >
> > > >  /* *well, except for TEX on level 2 large pages, of course :( */
> > > >  #define ARM_V7S_CONT_PAGE_TEX_SHIFT    6
> > > > @@ -183,13 +185,22 @@ static dma_addr_t __arm_v7s_dma_addr(void *pages)
> > > >  static arm_v7s_iopte paddr_to_iopte(phys_addr_t paddr, int lvl,
> > > >                                     struct io_pgtable_cfg *cfg)
> > > >  {
> > > > -       return paddr & ARM_V7S_LVL_MASK(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))
> > > > +                       pte |= ARM_V7S_ATTR_MTK_PA_BIT32;
> > > > +               if (paddr & BIT_ULL(33))
> > > > +                       pte |= ARM_V7S_ATTR_MTK_PA_BIT33;
> > > > +       }
> > > > +       return pte;
> > > >  }
> > > >
> > > >  static phys_addr_t iopte_to_paddr(arm_v7s_iopte pte, int lvl,
> > > >                                   struct io_pgtable_cfg *cfg)
> > > >  {
> > > >         arm_v7s_iopte mask;
> > > > +       phys_addr_t paddr;
> > > >
> > > >         if (ARM_V7S_PTE_IS_TABLE(pte, lvl))
> > > >                 mask = ARM_V7S_TABLE_MASK;
> > > > @@ -198,7 +209,14 @@ static phys_addr_t iopte_to_paddr(arm_v7s_iopte pte, int lvl,
> > > >         else
> > > >                 mask = ARM_V7S_LVL_MASK(lvl);
> > > >
> > > > -       return pte & mask;
> > > > +       paddr = pte & mask;
> > > > +       if (cfg->quirks & IO_PGTABLE_QUIRK_ARM_MTK_4GB) {
> > > > +               if (pte & ARM_V7S_ATTR_MTK_PA_BIT32)
> > > > +                       paddr |= BIT_ULL(32);
> > > > +               if (pte & ARM_V7S_ATTR_MTK_PA_BIT33)
> > > > +                       paddr |= BIT_ULL(33);
> > > > +       }
> > > > +       return paddr;
> > > >  }
> > > >
> > > >  static arm_v7s_iopte *iopte_deref(arm_v7s_iopte pte, int lvl,
> > > > @@ -315,9 +333,6 @@ static arm_v7s_iopte arm_v7s_prot_to_pte(int prot, int lvl,
> > > >         if (lvl == 1 && (cfg->quirks & IO_PGTABLE_QUIRK_ARM_NS))
> > > >                 pte |= ARM_V7S_ATTR_NS_SECTION;
> > > >
> > > > -       if (cfg->quirks & IO_PGTABLE_QUIRK_ARM_MTK_4GB)
> > > > -               pte |= ARM_V7S_ATTR_MTK_4GB;
> > > > -
> > >
> > > So despite getting lost in the details, I guess the reason it's okay
> > > that this goes from unconditional to conditional on bit32 is that
> > > before, with the older chips, all physical addresses were above 4GB,
> > > so we'll always see PA's above 4GB?
> > >
> > > >         return pte;
> > > >  }
> > > >
> > > > @@ -504,7 +519,9 @@ static int arm_v7s_map(struct io_pgtable_ops *ops, unsigned long iova,
> > > >         if (!(prot & (IOMMU_READ | IOMMU_WRITE)))
> > > >                 return 0;
> > > >
> > > > -       if (WARN_ON(upper_32_bits(iova) || upper_32_bits(paddr)))
> > > > +       if (WARN_ON(upper_32_bits(iova)) ||
> > > > +           WARN_ON(upper_32_bits(paddr) &&
> > > > +                   !(iop->cfg.quirks & IO_PGTABLE_QUIRK_ARM_MTK_4GB)))
> > > >                 return -ERANGE;
> > > >
> > > >         ret = __arm_v7s_map(data, iova, paddr, size, prot, 1, data->pgd);
> > > > diff --git a/drivers/iommu/io-pgtable.h b/drivers/iommu/io-pgtable.h
> > > > index 47d5ae5..69db115 100644
> > > > --- a/drivers/iommu/io-pgtable.h
> > > > +++ b/drivers/iommu/io-pgtable.h
> > > > @@ -62,10 +62,9 @@ struct io_pgtable_cfg {
> > > >          *      (unmapped) entries but the hardware might do so anyway, perform
> > > >          *      TLB maintenance when mapping as well as when unmapping.
> > > >          *
> > > > -        * IO_PGTABLE_QUIRK_ARM_MTK_4GB: (ARM v7s format) Set bit 9 in all
> > > > -        *      PTEs, for Mediatek IOMMUs which treat it as a 33rd address bit
> > > > -        *      when the SoC is in "4GB mode" and they can only access the high
> > > > -        *      remap of DRAM (0x1_00000000 to 0x1_ffffffff).
> > > > +        * IO_PGTABLE_QUIRK_ARM_MTK_4GB: (ARM v7s format) MediaTek IOMMUs extend
> > > > +        *      to support up to 34 bits PA where the bit32 and bit33 are
> > > > +        *      encoded in the bit9 and bit4 of the PTE respectively.
> > > >          *
> > > >          * IO_PGTABLE_QUIRK_NO_DMA: Guarantees that the tables will only ever
> > > >          *      be accessed by a fully cache-coherent IOMMU or CPU (e.g. for a
> > > > diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> > > > index 189d1b5..ae1aa5a 100644
> > > > --- a/drivers/iommu/mtk_iommu.c
> > > > +++ b/drivers/iommu/mtk_iommu.c
> > > > @@ -367,12 +367,16 @@ 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->plat_data->has_4gb_mode && data->enable_4GB)
> > > > +               paddr |= BIT_ULL(32);
> > > > +
> > >
> > > Ok here's where I get lost. How is this okay? Is the same physical RAM
> > > accessible at multiple locations in the physical address space? Won't
> > > this map an iova to a different pa than the one requested?
> >
> > In 4GB mode, HW will remap 0x4000_0000-0x1_3fff_ffff to 0x1_0000_0000-
> > 0x1_ffff_ffff. M4U help multimedia HW access dram, thus from M4U point
> > of view, the dram always is 0x1_0000_0000 to 0x1_ffff_ffff.
> >
> > The detailed mapping relationship is like this:
> >
> > 0x4000_0000  -0xffff_ffff   map to 0x1_4000_0000 - 0x1_ffff_ffff.
> > 0x1_0000_0000-0x1_3fff_ffff map to 0x1_0000_0000 - 0x1_3fff_ffff.
> >
> > Thus, we can only add bit32 for the PA in the 4GB mode.
> 
> Ok, I think I get it now. This thread really helped:
> https://patchwork.kernel.org/patch/8402211/
> 
> So from what I understand basically the same DRAM exists in two places:
> 0000_0000 - ffff_ffff, and is also available in
> 1_0000_0000 - 1_ffff_ffff
> 
> ...except that the peripherals are located in 0000_0000 - 3ffff_ffff,
> so that first GB of RAM is not visible at the lower address. I'm
> gathering this was in fact the motivation for 4GB mode. The important
> part is that address 4000_0000 == 1_4000_0000.
> 
> Then there was also some quirk of the IOMMU where it refused to access
> addresses below 4GB. But those same addresses are accessible by ORing
> in bit 32, so you just always do that and you're good to go.
> 
> Ok so now I can use that to understand this refactoring:
> * You used to always return an address above 4GB in
> mtk_iommu_iova_to_phys. I don't fully get how that worked, since it
> seems like you'd start returning PAs to the rest of the system that
> were outside of the range 4000_0000 - 1_3fff_ffff, but okay, you're no

I'm not sure I follow this. From the SW point view, the dram is
0x4000_0000 - 0x1_3fff_ffff. there is no memory outside it.

But there is really a issue in the mtk_iommu_iova_to_phys in the
4gb_mode.

Currently in the 4gb mode, I always add BIT32 for all the memory, then
the PA returned by the mtk_iommu_iova_to_phys(in v7s) always
is from 0x1_0000_0000 to 0x1_ffff_ffff. But the SW still expect the PA
is from 0x4000_0000 - 0x1_3fff_ffff. Thus, I guess I will add a new
patch like this:

@@ -418,6 +418,7 @@ static phys_addr_t mtk_iommu_iova_to_phys(struct
iommu_domain *domain,
 					  dma_addr_t iova)
 {
 	struct mtk_iommu_domain *dom = to_mtk_domain(domain);
+	struct mtk_iommu_data *data = mtk_iommu_get_m4u_data();
 	unsigned long flags;
 	phys_addr_t pa;
 
@@ -425,6 +426,11 @@ 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);
 
+	/* Discard bit32 if pa is 0x1_4000_0000 -0x1_ffff_ffff in 4GB mode. */
+	if (data->plat_data->has_4gb_mode && data->enable_4GB &&
+	    pa >= 0x140000000)
+		paddr &= ~BIT_ULL(32);
+
 	return pa;
 }


> longer doing that there, so I won't worry about it.
> * Now, if you're in the 4GB mode, you just slam the bit in the PTE in
> mtk_iommu_map, which seems like the right thing to do.
> * The general functions in io-pgtable-arm-v7s.c now carefully reflect
> bits 32 & 33 in the PTE, since the new IOMMUs don't have the weird
> restriction of staying above 4GB, and there's not this weird 4GB
> aliasing mode going on (which I think would be a clearer name for this
> feature: has_4gb_alias).

A more beautiful name. But our internal and all the CODA call this "4GB
mode"..thus I'd like to keep it....

> 
> >
> > >
> > > Also, you could have rolled the has_4gb_mode check into whether or not
> > > you set enable_4GB. Then you're doing the check for has_4gb_mode once,
> > > rather than on every map call.
> >
> > "has_4gb_mode" means this SoC support 4GB mode.
> > "enable_4GB" means whether the current dram size is 4GB.
> 
> Right. But your use of the variable as well as it's name suggest that
> it really means "is 4GB aliasing mode on", not "does the system have
> >=4GB of RAM". You could reduce the map function to one conditional if
> you treated the variable that way. Then the only things that would
> need to change would be:
> * Add an extra conditional in probe that would only set enable_4GB if
> has_4gb_mode is set.

I guess I still don't get this. the enable_4GB and has_4gb_mode are not
the same. Take mt8173 as a example when its dram size is 2G. it
has_4gb_mode, but we can not enable_4GB at that time.(if dram size is
2G, the HW will not remap the PA address, we can not add BIT32 at that
time.)

> * in mtk_iommu_domain_finalize, you could just always set the MTK
> quirk, since if you have <4GB of RAM, those bits will never get set in
> the PTEs anyway.

oh. Yes. this looks right.

> * I suspect mtk_iommu_hw_init would continue to work as-is, since
> everything that has vld_pa_rng also has has_4gb_mode.

mt8173 has 4gb_mode but it doesn't has vld_pa_rng.

> 
> -Evan