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From: Will Deacon <will@kernel.org>
To: Robin Murphy <robin.murphy@arm.com>
Cc: youlin.pei@mediatek.com, devicetree@vger.kernel.org,
	Nicolas Boichat <drinkcat@chromium.org>,
	cui.zhang@mediatek.com, srv_heupstream@mediatek.com,
	Tomasz Figa <tfiga@google.com>, Joerg Roedel <joro@8bytes.org>,
	linux-kernel@vger.kernel.org, Evan Green <evgreen@chromium.org>,
	chao.hao@mediatek.com, iommu@lists.linux-foundation.org,
	Rob Herring <robh+dt@kernel.org>,
	linux-mediatek@lists.infradead.org,
	linux-arm-kernel@lists.infradead.org,
	Matthias Brugger <matthias.bgg@gmail.com>,
	ming-fan.chen@mediatek.com, anan.sun@mediatek.com,
	Matthias Kaehlcke <mka@chromium.org>,
	Yong Wu <yong.wu@mediatek.com>
Subject: Re: [PATCH v10 09/23] iommu/io-pgtable-arm-v7s: Extend to support PA[33:32] for MediaTek
Date: Thu, 22 Aug 2019 12:28:36 +0100
Message-ID: <20190822112836.efodtwu3souq3uwa@willie-the-truck> (raw)
In-Reply-To: <e6652176-763d-5298-9e10-8c1fbe1b3c0d@arm.com>

On Thu, Aug 22, 2019 at 11:57:11AM +0100, Robin Murphy wrote:
> 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 ;)

You're quite right, although we live in a world where GCC shouts at us about
missing comments in switch statements so I think my worry was justified!

> > 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;

^^ Apparantly, I left the bracketting here as an exercise to the reader.

> > 
> > 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.

Ok, great. Yong Wu -- are you ok respinning with the above + missing
brackets?

Will

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Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-21 13:53 [PATCH v10 00/23] MT8183 IOMMU SUPPORT Yong Wu
2019-08-21 13:53 ` [PATCH v10 01/23] dt-bindings: mediatek: Add binding for mt8183 IOMMU and SMI Yong Wu
2019-08-21 13:53 ` [PATCH v10 02/23] iommu/mediatek: Use a struct as the platform data Yong Wu
2019-08-21 13:53 ` [PATCH v10 03/23] memory: mtk-smi: Use a general config_port interface Yong Wu
2019-08-21 13:53 ` [PATCH v10 04/23] memory: mtk-smi: Use a struct for the platform data for smi-common Yong Wu
2019-08-21 13:53 ` [PATCH v10 05/23] iommu/mediatek: Fix iova_to_phys PA start for 4GB mode Yong Wu
2019-08-21 13:53 ` [PATCH v10 06/23] iommu/io-pgtable-arm-v7s: Add paddr_to_iopte and iopte_to_paddr helpers Yong Wu
2019-08-21 13:53 ` [PATCH v10 07/23] iommu/io-pgtable-arm-v7s: Use ias/oas to check the valid iova/pa Yong Wu
2019-08-21 15:25   ` Will Deacon
2019-08-21 13:53 ` [PATCH v10 08/23] iommu/io-pgtable-arm-v7s: Rename the quirk from MTK_4GB to MTK_EXT Yong Wu
2019-08-21 15:25   ` Will Deacon
2019-08-21 13:53 ` [PATCH v10 09/23] iommu/io-pgtable-arm-v7s: Extend to support PA[33:32] for MediaTek Yong Wu
2019-08-21 15:24   ` Will Deacon
2019-08-21 15:34     ` Robin Murphy
2019-08-21 16:35       ` Will Deacon
2019-08-22  8:59       ` Yong Wu
2019-08-22  8:56     ` Yong Wu
2019-08-22 10:08       ` Will Deacon
2019-08-22 10:08       ` Robin Murphy
2019-08-22 10:17         ` Will Deacon
2019-08-22 10:57           ` Robin Murphy
2019-08-22 11:28             ` Will Deacon [this message]
2019-08-22 12:05               ` Yong Wu
2019-08-22 17:14                 ` Will Deacon
2019-08-21 13:53 ` [PATCH v10 10/23] iommu/mediatek: Adjust the PA for the 4GB Mode Yong Wu
2019-08-21 13:53 ` [PATCH v10 11/23] iommu/mediatek: Add bclk can be supported optionally Yong Wu
2019-08-21 13:53 ` [PATCH v10 12/23] iommu/mediatek: Add larb-id remapped support Yong Wu
2019-08-21 13:53 ` [PATCH v10 13/23] iommu/mediatek: Refine protect memory definition Yong Wu
2019-08-21 13:53 ` [PATCH v10 14/23] iommu/mediatek: Move reset_axi into plat_data Yong Wu
2019-08-21 13:53 ` [PATCH v10 15/23] iommu/mediatek: Move vld_pa_rng " Yong Wu
2019-08-21 13:53 ` [PATCH v10 16/23] memory: mtk-smi: Add gals support Yong Wu
2019-08-21 13:53 ` [PATCH v10 17/23] iommu/mediatek: Add mt8183 IOMMU support Yong Wu
2019-08-21 13:53 ` [PATCH v10 18/23] iommu/mediatek: Add mmu1 support Yong Wu
2019-08-21 13:53 ` [PATCH v10 19/23] memory: mtk-smi: Invoke pm runtime_callback to enable clocks Yong Wu
2019-08-21 13:53 ` [PATCH v10 20/23] memory: mtk-smi: Add bus_sel for mt8183 Yong Wu
2019-08-21 13:53 ` [PATCH v10 21/23] iommu/mediatek: Fix VLD_PA_RNG register backup when suspend Yong Wu
2019-08-21 13:53 ` [PATCH v10 22/23] memory: mtk-smi: Get rid of need_larbid Yong Wu
2019-08-21 13:53 ` [PATCH v10 23/23] iommu/mediatek: Clean up struct mtk_smi_iommu Yong Wu
2019-08-22 14:07   ` Matthias Brugger

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