Re: [PATCH v6 06/22] iommu/io-pgtable-arm-v7s: Extend MediaTek 4GB Mode

[Evan Green]

On Sun, Feb 17, 2019 at 1:07 AM Yong Wu <yong.wu@xxxxxxxxxxxx> 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.
>
> 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@xxxxxxxxxxxx>
> Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx>
> ---
> Comparing the previous version, I add MTK_4GB quirk always since mtk_iommu
> has already controlled the PA itself. Helped from Evan.

Thanks for all the explanation on this one. I think I understand it
now, and it looks good to me.

Reviewed-by: Evan Green <evgreen@xxxxxxxxxxxx>