Re: [PATCH v9 08/21] iommu/io-pgtable-arm-v7s: Extend MediaTek 4GB Mode
From: Yong Wu
Date: Fri Aug 16 2019 - 03:22:37 EST
On Thu, 2019-08-15 at 12:50 +0100, Will Deacon wrote:
> Ok, I think speaking to Robin helped me a bit with this...
> On Thu, Aug 15, 2019 at 06:18:38PM +0800, Yong Wu wrote:
> > On Thu, 2019-08-15 at 10:51 +0100, Will Deacon wrote:
> > > On Thu, Aug 15, 2019 at 04:47:49PM +0800, Yong Wu wrote:
> > > > On Wed, 2019-08-14 at 15:41 +0100, Will Deacon wrote:
> > > > > 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)
> > > > > 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 . 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.
> > >
> > > I think this is probably at the heart of my misunderstanding. What is so
> > > special about PAs (is this HW PA or CPU PA?) below 0x40000000? Is this RAM
> > > or something else?
> > SRAM and HW register that IOMMU can not access.
> Ok, so redrawing your table from above, I think we can say something like:
> CPU Physical address
> 0G 1G 2G 3G 4G 5G
> IOMMU output physical address
> 4G 5G 6G 7G 8G
> Do you agree?
> If so, what happens to region 'A' (the I/O region) in the
> IOMMU output physical address space. Is it accessible?
No. IOMMU can not access region 'A' above.
> Anyway, I think it's the job of the driver to convert between the two
> address spaces, so that:
> - On ->map(), bit 32 of the CPU physical address is set before calling
> into the iopgtable code
> - The result from ->iova_to_phys() should be the result from the
> iopgtable code, but with the top bit cleared for addresses over
> This assumes that:
> 1. We're ok setting bit 9 in the ptes mapping region 'E'.
> 2. The IOMMU page-table walker uses CPU physical addresses
> Are those true?
Yes. Then this patch would be close to the one I sent in v8.
Do I need to split this patch into 2 ones?:
a).the pagetable code that support 34bit PA when MTK quirk is enabled.
It only has the symmetric code handle BIT32/BIT33. Besides, I will add
CONFIG_PHYS_ADDR_T_64BIT in the iopte_to_addr as commented before.
b) MTK code that apply the special "4gb mode" flow. And the "oas" will
always is 34 bit since v7s has already supported our case.