Re: [PATCH v8 07/21] iommu/io-pgtable-arm-v7s: Extend MediaTek 4GB Mode

[Yong Wu <yong.wu@mediatek.com>]

On Wed, 2019-07-17 at 15:23 +0100, Will Deacon wrote:
> On Wed, Jul 17, 2019 at 08:44:19PM +0800, Yong Wu wrote:
> > On Mon, 2019-07-15 at 10:51 +0100, Will Deacon wrote:
> > > On Sun, Jul 14, 2019 at 12:41:20PM +0800, Yong Wu wrote:
> > > > @@ -742,7 +763,9 @@ static struct io_pgtable
> > > > *arm_v7s_alloc_pgtable(struct io_pgtable_cfg *cfg,
> > > >  {
> > > >  	struct arm_v7s_io_pgtable *data;
> > > >  
> > > > -	if (cfg->ias > ARM_V7S_ADDR_BITS || cfg->oas > ARM_V7S_ADDR_BITS)
> > > > +	if (cfg->ias > ARM_V7S_ADDR_BITS ||
> > > > +	    (cfg->oas > ARM_V7S_ADDR_BITS &&
> > > > +	     !(cfg->quirks & IO_PGTABLE_QUIRK_ARM_MTK_EXT)))
> > > >  		return NULL;
> > > 
> > > I think you can rework this to do something like:
> > > 
> > > 	if (cfg->ias > ARM_V7S_ADDR_BITS)
> > > 		return NULL;
> > > 
> > > 	if (cfg->quirks & IO_PGTABLE_QUIRK_ARM_MTK_EXT) {
> > > 		if (!IS_ENABLED(CONFIG_PHYS_ADDR_T_64BIT))
> > > 			cfg->oas = min(cfg->oas, ARM_V7S_ADDR_BITS);
> > > 		else if (cfg->oas > 34)
> > > 			return NULL;
> > > 	} else if (cfg->oas > ARM_V7S_ADDR_BITS) {
> > > 		return NULL;
> > > 	}
> > > 
> > > so that we clamp the oas when phys_addr_t is 32-bit for you. That should
> > > allow you to remove lots of the checking from iopte_to_paddr() too if you
> > > check against oas in the map() function.
> > > 
> > > Does that make sense?
> > 
> > Of course I'm ok for this. I'm only afraid that this function has
> > already 3 checking "if (x) return NULL", Here we add a new one and so
> > many lines... Maybe the user should guarantee the right value of oas.
> > How about move it into mtk_iommu.c?
> > 
> > About the checking of iopte_to_paddr, I can not remove them. I know it
> > may be a bit special and not readable. Hmm, I guess I should use a MACRO
> > instead of the hard code 33 for the special 4GB mode case.
> 
> Why can't you just do something like:
> 
> 	if (!(cfg->quirks & IO_PGTABLE_QUIRK_ARM_MTK_EXT))
> 		return paddr;
> 
> 	if (pte & ARM_V7S_ATTR_MTK_PA_BIT33)
> 		paddr |= BIT_ULL(33);

OK here.

> 
> 	if (pte & ARM_V&S_ATTR_MTK_PA_BIT32)
> 		paddr |= BIT_ULL(32);

No here, The flow is a bit special for 4GB mode here.

This is the detailed remap relationship for our 4GB mode.
           CPU PA               ->    HW PA
register: 0x0 ~ 0x3fff_ffff
dram 1G:0x4000_0000~0x7fff_ffff ->0x1_4000_0000~0x1_7fff_ffff(Add bit32)
dram 2G:0x8000_0000~0xbfff_ffff ->0x1_8000_0000~0x1_bfff_ffff(Add bit32)
dram 3G:0xc000_0000~0xffff_ffff ->0x1_c000_0000~0x1_ffff_ffff(Add bit32)
dram 4G:0x1_0000_0000~0x1_3fff_ffff->0x1_0000_0000~0x1_3fff_ffff

Thus, in the 4GB mode, we should add always add bit9 in pte(for bit32
PA). But we can not always add bit32 in the iova_to_phys. The valid PA
range should be 0x4000_0000 - 0x1_3fff_ffff. Thus, we can only add bit32
when the PA in pte < 0x4000_0000, keep it as-is if the PA in pte located
from 0x4000_0000 to 0xffff_ffff.

This issue exist all the time after we added 4GB mode for mt8173.

Thus, I have to add a special flow for 4gb mode here:

	/* 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;
> 
> The diff I sent previously sanitises the oas at init time, and then you
> can just enforce it in map().
> 
> Will