On Tue, Sep 15, 2020 at 09:16:15PM +0800, Zhen Lei wrote: > Currently, only support the kernels where the base of physical memory is > at a 16MiB boundary. Because the add/sub instructions only contains 8bits > unrotated value. But we can use one more "add/sub" instructions to handle > bits 23-16. The performance will be slightly affected. > > Since most boards meet 16 MiB alignment, so add a new configuration > option ARM_PATCH_PHYS_VIRT_RADICAL (default n) to control it. Say Y if > anyone really needs it. > > All r0-r7 (r1 = machine no, r2 = atags or dtb, in the start-up phase) are > used in __fixup_a_pv_table() now, but the callee saved r11 is not used in > the whole head.S file. So choose it. > > Because the calculation of "y = x + __pv_offset[63:24]" have been done, > so we only need to calculate "y = y + __pv_offset[23:16]", that's why > the parameters "to" and "from" of __pv_stub() and __pv_add_carry_stub() > in the scope of CONFIG_ARM_PATCH_PHYS_VIRT_RADICAL are all passed "t" > (above y). > > Signed-off-by: Zhen Lei <thunder.leiz...@huawei.com> > --- > arch/arm/Kconfig | 18 +++++++++++++++++- > arch/arm/include/asm/memory.h | 16 +++++++++++++--- > arch/arm/kernel/head.S | 25 +++++++++++++++++++------ > 3 files changed, 49 insertions(+), 10 deletions(-) > > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig > index e00d94b16658765..19fc2c746e2ce29 100644 > --- a/arch/arm/Kconfig > +++ b/arch/arm/Kconfig > @@ -240,12 +240,28 @@ config ARM_PATCH_PHYS_VIRT > kernel in system memory. > > This can only be used with non-XIP MMU kernels where the base > - of physical memory is at a 16MB boundary. > + of physical memory is at a 16MiB boundary. > > Only disable this option if you know that you do not require > this feature (eg, building a kernel for a single machine) and > you need to shrink the kernel to the minimal size. > > +config ARM_PATCH_PHYS_VIRT_RADICAL > + bool "Support PHYS_OFFSET minimum aligned at 64KiB boundary" > + default n
Please drop the "default n" - this is the default anyway. > @@ -236,6 +243,9 @@ static inline unsigned long __phys_to_virt(phys_addr_t x) > * in place where 'r' 32 bit operand is expected. > */ > __pv_stub((unsigned long) x, t, "sub", __PV_BITS_31_24); > +#ifdef CONFIG_ARM_PATCH_PHYS_VIRT_RADICAL > + __pv_stub((unsigned long) t, t, "sub", __PV_BITS_23_16); t is already unsigned long, so this cast is not necessary. I've been debating whether it would be better to use "movw" for this for ARMv7. In other words: movw tmp, #16-bit adds %Q0, %1, tmp, lsl #16 adc %R0, %R0, #0 It would certainly be less instructions, but at the cost of an additional register - and we'd have to change the fixup code to know about movw. Thoughts? -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!