On 24/02/2021 21:35, Florian Fainelli wrote: > > > On 2/24/2021 12:25 PM, Christoph Hellwig wrote: >> 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. > > That would work. The use case described by Robin is highly unlikely to > exist on the Pi4 given that you cannot easily access the PCIe bus and > plug an arbitrary GPU, so maybe there is nothing to do for framebuffer > memory. > Erf, not really, with the compute module ATX/ITX boards are being designed with a full PCIe connector like: https://www.indiegogo.com/projects/over-board-raspberry-pi-4-mini-itx-motherboard/#/ Neil
