Re: [PATCH v10 09/23] iommu/io-pgtable-arm-v7s: Extend to support PA[33:32] for MediaTek

[Robin Murphy]

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@xxxxxxxxxxxx>
> > > ---
> > >   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)

We shouldn't need to care about the size of phys_addr_t either way - the 
fact is that the MTK format can still encode up to 34 bits of PA 
regardless of whether callers can actually pass addresses that large.

Robin.