Re: [PATCH v3 11/24] iommu/io-pgtable-arm-v7s: Quad lvl1 pgtable for MediaTek

Robin Murphy
2020-10-26T11:37:29Z

On 2020-10-26 07:41, Yong Wu wrote:
> On Fri, 2020-10-23 at 15:10 +0100, Robin Murphy wrote:
>> On 2020-09-30 08:06, Yong Wu wrote:
>>> The standard input iova bits is 32. MediaTek quad the lvl1 pagetable
>>> (4 * lvl1). No change for lvl2 pagetable. Then the iova bits can reach
>>> 34bit.
>>>
>>> Signed-off-by: Yong Wu <yong.wu@mediatek.com>
>>> ---
>>> drivers/iommu/io-pgtable-arm-v7s.c | 13 ++++++++++---
>>> drivers/iommu/mtk_iommu.c | 2 +-
>>> 2 files changed, 11 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/iommu/io-pgtable-arm-v7s.c b/drivers/iommu/io-pgtable-arm-v7s.c
>>> index 8362fdf76657..306bae2755ed 100644
>>> --- a/drivers/iommu/io-pgtable-arm-v7s.c
>>> +++ b/drivers/iommu/io-pgtable-arm-v7s.c
>>> @@ -50,10 +50,17 @@
>>> */
>>> #define ARM_V7S_ADDR_BITS 32
>>> #define _ARM_V7S_LVL_BITS(lvl) (16 - (lvl) * 4)
>>> +/* MediaTek: totally 34bits, 14bits at lvl1 and 8bits at lvl2. */
>>> +#define _ARM_V7S_LVL_BITS_MTK(lvl) (20 - (lvl) * 6)
>>
>> This should defined in terms of both lvl and cfg->ias. The formula here
>> is nothing more than a disgusting trick I made up since a linear
>> interpolation happened to fit the required numbers. That said, all of
>> these bits pretending that short-descriptor is a well-defined recursive
>> format only served to allow the rest of the code to look more like the
>> LPAE code - IIRC they've already diverged a fair bit since then, so
>> frankly a lot of this could stand to be unpicked and made considerably
>> clearer by simply accepting that level 1 and level 2 are different from
>> each other.
>
> If the formula is not good and make it clearer, How about this?
>
>
> /*
> * We have 32 bits total; 12 bits resolved at level 1, 8 bits at level
> 2,
> -* and 12 bits in a page. With some carefully-chosen coefficients we can
> -* hide the ugly inconsistencies behind these macros and at least let
> the
> -* rest of the code pretend to be somewhat sane.
> +* and 12 bits in a page.
> +*
> +* MediaTek extend 2 bits to reach 34 bits, 14 bits at lvl1 and 8 bits
> at lvl2.
> */
>
> -#define _ARM_V7S_LVL_BITS(lvl) (16 - (lvl) * 4)
> +#define _ARM_V7S_LVL1_BITS_NR(cfg) (((cfg)->ias == 32) ? 12 : 14)
> +#define _ARM_V7S_LVL2_BITS_NR 8
> +
> +#define _ARM_V7S_LVL_BITS(lvl, cfg) \
> + (((lvl) == 1) ? _ARM_V7S_LVL1_BITS_NR(cfg):_ARM_V7S_LVL2_BITS_NR)

Well, I'd have gone for something really simple and clear like:

#define ARM_V7S_LVL_BITS(lvl, cfg) ((lvl) == 1 ? (cfg)->ias - 20 : 8)
#define ARM_V7S_LVL_SHIFT(lvl) ((lvl) == 1 ? 20 : 12)

Then maybe see if enough of the users could resolve lvl significantly
earlier to make it worth splitting things up further.

Robin.

>>> #define ARM_V7S_LVL_SHIFT(lvl) (ARM_V7S_ADDR_BITS - (4 + 8 * (lvl)))
>>> #define ARM_V7S_TABLE_SHIFT 10
>>>
>>> -#define ARM_V7S_PTES_PER_LVL(lvl, cfg) (1 << _ARM_V7S_LVL_BITS(lvl))
>>> +#define ARM_V7S_PTES_PER_LVL(lvl, cfg) ({ \
>>> + int _lvl = lvl; \
>>> + !arm_v7s_is_mtk_enabled(cfg) ? \
>>> + (1 << _ARM_V7S_LVL_BITS(_lvl)) : (1 << _ARM_V7S_LVL_BITS_MTK(_lvl));\
>>> +})
>>> +
>>> #define ARM_V7S_TABLE_SIZE(lvl, cfg) \
>>> (ARM_V7S_PTES_PER_LVL(lvl, cfg) * sizeof(arm_v7s_iopte))
>>>
>>> @@ -63,7 +70,7 @@
>>> #define _ARM_V7S_IDX_MASK(lvl, cfg) (ARM_V7S_PTES_PER_LVL(lvl, cfg) - 1)
>>> #define ARM_V7S_LVL_IDX(addr, lvl, cfg) ({ \
>>> int _l = lvl; \
>>> - ((u32)(addr) >> ARM_V7S_LVL_SHIFT(_l)) & _ARM_V7S_IDX_MASK(_l, cfg); \
>>> + ((addr) >> ARM_V7S_LVL_SHIFT(_l)) & _ARM_V7S_IDX_MASK(_l, cfg); \
>>> })
>>>
>>> /*
>>> @@ -755,7 +762,7 @@ 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)
>>> + if (cfg->ias > (arm_v7s_is_mtk_enabled(cfg) ? 34 : ARM_V7S_ADDR_BITS))
>>> return NULL;
>>>
>>> if (cfg->oas > (arm_v7s_is_mtk_enabled(cfg) ? 35 : ARM_V7S_ADDR_BITS))
>>> diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
>>> index f6a2e3eb59d2..6e85c9976a33 100644
>>> --- a/drivers/iommu/mtk_iommu.c
>>> +++ b/drivers/iommu/mtk_iommu.c
>>> @@ -316,7 +316,7 @@ static int mtk_iommu_domain_finalise(struct mtk_iommu_domain *dom)
>>> IO_PGTABLE_QUIRK_TLBI_ON_MAP |
>>> IO_PGTABLE_QUIRK_ARM_MTK_EXT,
>>> .pgsize_bitmap = mtk_iommu_ops.pgsize_bitmap,
>>> - .ias = 32,
>>> + .ias = 34,
>>> .oas = 35,
>>> .tlb = &mtk_iommu_flush_ops,
>>> .iommu_dev = data->dev,
>>>