On Wed, Feb 24, 2021 at 08:55:10AM -0800, Florian Fainelli wrote: > > Working around kernel I/O accessors is all very well, but another > > concern for PCI in particular is when things like framebuffer memory can > > get mmap'ed into userspace (or even memremap'ed within the kernel). Even > > in AArch32, compiled code may result in 64-bit accesses being generated > > depending on how the CPU and interconnect handle LDRD/STRD/LDM/STM/etc., > > so it's basically not safe to ever let that happen at all. > > Agreed, this makes finding a generic solution a tiny bit harder. Do you > have something in mind Nicolas? The only workable solution is a new bool 64bit_mmio_supported(void) check that is used like: if (64bit_mmio_supported()) readq(foodev->regs, REG_OFFSET); else lo_hi_readq(foodev->regs, REG_OFFSET); where 64bit_mmio_supported() return false for all 32-bit kernels, true for all non-broken 64-bit kernels and is an actual function for arm64 multiplatforms builds that include te RPi quirk. The above would then replace the existing magic from the <linux/io-64-nonatomic-lo-hi.h> and <linux/io-64-nonatomic-hi-lo.h> headers.
