Re: [PATCH 2/5] iommu/mediatek: Add mt8173 IOMMU driver

[Will Deacon <will.deacon@arm.com>]

On Mon, Mar 09, 2015 at 12:11:43PM +0000, Yong Wu wrote:
> On Fri, 2015-03-06 at 10:58 +0000, Will Deacon wrote:
> > On Fri, Mar 06, 2015 at 10:48:17AM +0000, yong.wu@mediatek.com wrote:
> > > From: Yong Wu <yong.wu@mediatek.com>
> > > 
> > > This patch adds support for mediatek m4u (MultiMedia Memory Management Unit).
> > > Currently this only supports m4u gen 2 with 2 levels of page table on mt8173.
> > 
> > [...]
> > 
> > > +/* 2 level pagetable: pgd -> pte */
> > > +#define F_PTE_TYPE_GET(regval)  (regval & 0x3)
> > > +#define F_PTE_TYPE_LARGE         BIT(0)
> > > +#define F_PTE_TYPE_SMALL         BIT(1)
> > > +#define F_PTE_B_BIT              BIT(2)
> > > +#define F_PTE_C_BIT              BIT(3)
> > > +#define F_PTE_BIT32_BIT          BIT(9)
> > > +#define F_PTE_S_BIT              BIT(10)
> > > +#define F_PTE_NG_BIT             BIT(11)
> > > +#define F_PTE_PA_LARGE_MSK            (~0UL << 16)
> > > +#define F_PTE_PA_LARGE_GET(regval)    ((regval >> 16) & 0xffff)
> > > +#define F_PTE_PA_SMALL_MSK            (~0UL << 12)
> > > +#define F_PTE_PA_SMALL_GET(regval)    ((regval >> 12) & (~0))
> > > +#define F_PTE_TYPE_IS_LARGE_PAGE(pte) ((imu_pte_val(pte) & 0x3) == \
> > > +                                       F_PTE_TYPE_LARGE)
> > > +#define F_PTE_TYPE_IS_SMALL_PAGE(pte) ((imu_pte_val(pte) & 0x3) == \
> > > +                                       F_PTE_TYPE_SMALL)
> > 
> > This looks like the ARM short-descriptor format to me. Could you please
> > add a new page table format to the io-pgtable code, so that other IOMMU
> > drivers can make use of this? I know there was some interest in using
> > short descriptor for the ARM SMMU, for example.
>     Currently I not familiar with the io-pgtable,I may need some time
> for it and the ARM short-descriptor. 

Well, you can read the LPAE version I wrote in io-pgtable-arm.c for some
inspiration (it's used by arm-smmu.c and ipmmu-vmsa.c).

>     And there are some difference between mediatek's pagetable with the
> standard short-descriptor, like bit 9. we use it for the dram over 4GB.
> Then how should we do if there are some difference. 

That can easily be handled using a quirk (see, for example,
IO_PGTABLE_QUIRK_ARM_NS).

Will