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SubjectRe: [PATCH v10 09/23] iommu/io-pgtable-arm-v7s: Extend to support PA[33:32] for MediaTek
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On 2019-08-22 11:17 am, Will Deacon wrote:
> On Thu, Aug 22, 2019 at 11:08:58AM +0100, Robin Murphy wrote:
>> On 2019-08-22 9:56 am, Yong Wu wrote:
>>> On Wed, 2019-08-21 at 16:24 +0100, Will Deacon wrote:
>>>> On Wed, Aug 21, 2019 at 09:53:12PM +0800, Yong Wu wrote:
>>>>> MediaTek extend the arm v7s descriptor to support up to 34 bits PA where
>>>>> the bit32 and bit33 are encoded in the bit9 and bit4 of the PTE
>>>>> respectively. Meanwhile the iova still is 32bits.
>>>>>
>>>>> 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@mediatek.com>
>>>>> ---
>>>>> drivers/iommu/io-pgtable-arm-v7s.c | 32 +++++++++++++++++++++++++-------
>>>>> include/linux/io-pgtable.h | 7 +++----
>>>>> 2 files changed, 28 insertions(+), 11 deletions(-)
>>>>
>>>> [...]
>>>>
>>>>> @@ -731,7 +747,9 @@ 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)))
>>>>
>>>> Please can you instead change arm_v7s_alloc_pgtable() so that it allows an
>>>> ias of up to 34 when the IO_PGTABLE_QUIRK_ARM_MTK_EXT is set?
>>>
>>> Here I only simply skip the oas checking for our case. then which way do
>>> your prefer? something like you commented before:?
>>>
>>>
>>> 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;
>>> }
>>
>> All it should take is something like:
>>
>> if (cfg->quirks & IO_PGTABLE_QUIRK_ARM_MTK_EXT)
>> max_oas = 34;
>> else
>> max_oas = 32;
>> if (cfg->oas > max_oas)
>> return NULL;
>>
>> or even just:
>>
>> if (cfg->oas > 32 ||
>> (cfg->quirks & IO_PGTABLE_QUIRK_ARM_MTK_EXT && cfg->oas > 34))
>> return NULL;
>>
>> (and if we prefer the latter style, perhaps we could introduce some kind of
>> "is_mtk_4gb()" helper to save on verbosity)
>
> I wondered the same thing, but another place we'd want the check is in
> iopte_to_paddr() which probably needs the PHYS_ADDR_T check to avoid GCC
> warnings, although I didn't try it.

I'm pretty sure I confirmed that "paddr |= BIT_ULL(32)" doesn't warn
when phys_addt_t is 32-bit - it's well-defined unsigned integer
truncation after all, and if GCC starts warning about all the valid
no-op code it optimises away then it's going to run up against
IS_ENABLED() first and foremost ;)

> So if we did:
>
> static bool cfg_mtk_ext_enabled(struct io_pgtable_cfg *cfg)
> {
> return IS_ENABLED(CONFIG_PHYS_ADDR_T_64BIT) &&
> cfg->quirks & IO_PGTABLE_QUIRK_ARM_MTK_EXT;
> }
>
> Then I suppose we could do this in _alloc():
>
> if (cfg->oas > cfg_mtk_ext_enabled(cfg) ? 34 : ARM_V7S_ADDR_BITS)
> return NULL;
>
> and then this in iopte_to_paddr():
>
> [...]
>
> paddr = pte & mask;
> if (!cfg_mtk_ext_enabled(cfg))
> return paddr;
>
> if (pte & ARM_V7S_ATTR_MTK_PA_BIT32)
> paddr |= ...
>
> [...]
>
> What do you reckon?

Yeah, that's the general shape of things I was picturing - I'm not that
fussed about the PHYS_ADDR_T_64BIT thing, especially if it's wrapped up
in just one place, so if you do want to keep it as belt-and-braces I'll
just consider it a slight code size optimisation for 32-bit builds.

Robin.

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