On Fri, Mar 21, 2014 at 11:52:33PM +0000, Arnd Bergmann wrote: > On Friday 21 March 2014 23:27:24 Catalin Marinas wrote: > > On 21 Mar 2014, at 19:44, Christopher Covington <c...@codeaurora.org> wrote: > > > On 03/21/2014 12:27 PM, Catalin Marinas wrote: > > >>> diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig > > >>> index 1f8fed9..a62bcc9 100644 > > >>> --- a/arch/arm/mm/Kconfig > > >>> +++ b/arch/arm/mm/Kconfig > > >>> @@ -617,6 +617,7 @@ config ARM_LPAE > > >>> bool "Support for the Large Physical Address Extension" > > >>> depends on MMU && CPU_32v7 && !CPU_32v6 && !CPU_32v5 && \ > > >>> !CPU_32v4 && !CPU_32v3 > > >>> + select ARCH_DMA_ADDR_T_64BIT if VIRTIO_MMIO > > >> > > >> That's the wrong place to enable ARCH_DMA_ADDR_T_64BIT. Do you have a > > >> platform with >32-bit physical address space? If yes, it should be > > >> selected there. > > > > > > The platforms I'm currently using are models like the Versatile Express > > > RTSM/FVP. I can respin with changes to ARCH_VEXPRESS and ARCH_VIRT > > > instead. > > > > But do you use RAM beyond 32-bit on such models? > > I think the more important question here is what the normal behavior is > for these platforms. I believe in most cases you don't have RAM above > the boundary, so we should not enable the option by default as it can > have noticeable overhead (we'd turn it on all the time if it didn't). > > How about one of these two > > a) > > diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig > index 9ea4b7b..6e3b6db 100644 > --- a/arch/arm/mm/Kconfig > +++ b/arch/arm/mm/Kconfig > @@ -628,7 +628,9 @@ config ARCH_PHYS_ADDR_T_64BIT > def_bool ARM_LPAE > > config ARCH_DMA_ADDR_T_64BIT > - bool > + def_bool "Allow DMA to high (>4GB) addresses" > + depends on ARCH_PHYS_ADDR_T_64BIT > + default y > help
We should probably call this "Allow DMA to high (>4GB) _bus_ addresses" to distinguish it from the actual CPU physical address. > b) > > diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig > index 9ea4b7b..4a21b1e 100644 > --- a/arch/arm/mm/Kconfig > +++ b/arch/arm/mm/Kconfig [...] > config ARCH_PHYS_ADDR_T_64BIT > - def_bool ARM_LPAE > + bool "Support more than 4GB of physical address space" if EXPERT > + depends on ARM_LPAE > + default y I don't think I ever tested LPAE with ARCH_PHYS_ADDR_T_64BIT off. Even if you enable EXPERT, it's a risk that some bit shifting of phys_addr_t would break (the pte expects 64-bit entries). > config ARCH_DMA_ADDR_T_64BIT > - bool > + def_bool ARCH_PHYS_ADDR_T_64BIT I recall Russell objecting to this when we reviewed the LPAE patches because the CPU address is different from the bus address. I assume those arguments still stand. I would go for (a) but with individual SoCs still selecting ARCH_DMA_ADDR_T_64BIT explicitly if they expect bus addresses over 32-bit. -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
