linux-kernel - Re: [PATCH v8 07/21] iommu/io-pgtable-arm-v7s: Extend MediaTek 4GB Mode

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Message-ID: <20190717142339.wltamw6wktwixqqn@willie-the-truck>
Date:   Wed, 17 Jul 2019 15:23:40 +0100
From:   Will Deacon <will@...nel.org>
To:     Yong Wu <yong.wu@...iatek.com>
Cc:     youlin.pei@...iatek.com, devicetree@...r.kernel.org,
        Nicolas Boichat <drinkcat@...omium.org>,
        cui.zhang@...iatek.com, srv_heupstream@...iatek.com,
        chao.hao@...iatek.com, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, Evan Green <evgreen@...omium.org>,
        Tomasz Figa <tfiga@...gle.com>,
        iommu@...ts.linux-foundation.org, Rob Herring <robh+dt@...nel.org>,
        linux-mediatek@...ts.infradead.org,
        Matthias Brugger <matthias.bgg@...il.com>,
        yingjoe.chen@...iatek.com, anan.sun@...iatek.com,
        Robin Murphy <robin.murphy@....com>,
        Matthias Kaehlcke <mka@...omium.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v8 07/21] iommu/io-pgtable-arm-v7s: Extend MediaTek 4GB
 Mode

On Wed, Jul 17, 2019 at 08:44:19PM +0800, Yong Wu wrote:
> On Mon, 2019-07-15 at 10:51 +0100, Will Deacon wrote:
> > On Sun, Jul 14, 2019 at 12:41:20PM +0800, Yong Wu wrote:
> > > @@ -742,7 +763,9 @@ 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)))
> > >  		return NULL;
> > 
> > I think you can rework this to do something like:
> > 
> > 	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;
> > 	}
> > 
> > so that we clamp the oas when phys_addr_t is 32-bit for you. That should
> > allow you to remove lots of the checking from iopte_to_paddr() too if you
> > check against oas in the map() function.
> > 
> > Does that make sense?
> 
> Of course I'm ok for this. I'm only afraid that this function has
> already 3 checking "if (x) return NULL", Here we add a new one and so
> many lines... Maybe the user should guarantee the right value of oas.
> How about move it into mtk_iommu.c?
> 
> About the checking of iopte_to_paddr, I can not remove them. I know it
> may be a bit special and not readable. Hmm, I guess I should use a MACRO
> instead of the hard code 33 for the special 4GB mode case.

Why can't you just do something like:

	if (!(cfg->quirks & IO_PGTABLE_QUIRK_ARM_MTK_EXT))
		return paddr;

	if (pte & ARM_V7S_ATTR_MTK_PA_BIT33)
		paddr |= BIT_ULL(33);

	if (pte & ARM_V&S_ATTR_MTK_PA_BIT32)
		paddr |= BIT_ULL(32);

	return paddr;

The diff I sent previously sanitises the oas at init time, and then you
can just enforce it in map().

Will