Messages in this thread | | | Subject | Re: [PATCH v10 09/23] iommu/io-pgtable-arm-v7s: Extend to support PA[33:32] for MediaTek | From | Robin Murphy <> | Date | Thu, 22 Aug 2019 11:57:11 +0100 |
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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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