Re: [PATCH v6 06/20] iommu/io-pgtable-arm-v7s: Extend MediaTek 4GB Mode

Evan Green
2019-01-31T19:24:14Z

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
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).

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

-Evan