Hi, Ben, On 2016/11/9 7:16, Benjamin Herrenschmidt wrote: > On Tue, 2016-11-08 at 12:03 +0000, Mark Rutland wrote: >> On Tue, Nov 08, 2016 at 11:47:07AM +0800, zhichang.yuan wrote: >>> >>> For arm64, there is no I/O space as other architectural platforms, such as >>> X86. Most I/O accesses are achieved based on MMIO. But for some arm64 SoCs, >>> such as Hip06, when accessing some legacy ISA devices connected to LPC, those >>> known port addresses are used to control the corresponding target devices, for >>> example, 0x2f8 is for UART, 0xe4 is for ipmi-bt. It is different from the >>> normal MMIO mode in using. >> >> This has nothing to do with arm64. Hardware with this kind of indirect >> bus access could be integrated with a variety of CPU architectures. It >> simply hasn't been, yet. > > On some ppc's we also use similar indirect access methods for IOs. We > have a generic infrastructure for re-routing some memory or IO regions > to hooks. > I am interested on the generic infrastructure on PPC. Could you point out where those drivers are? want to take a look.. Thanks, Zhichang > On POWER8, our PCIe doesn't do IO at all, but we have an LPC bus behind > firmware calls ;-) We use that infrastructure to plumb in the LPC bus. > >>> To drive these devices, this patch introduces a method named indirect-IO. >>> In this method the in/out pair in arch/arm64/include/asm/io.h will be >>> redefined. When upper layer drivers call in/out with those known legacy port >>> addresses to access the peripherals, the hooking functions corrresponding to >>> those target peripherals will be called. Through this way, those upper layer >>> drivers which depend on in/out can run on Hip06 without any changes. >> >> As above, this has nothing to do with arm64, and as such, should live in >> generic code, exactly as we would do if we had higher-level ISA >> accessor ops. >> >> Regardless, given the multi-instance case, I don't think this is >> sufficient in general (and I think we need higher-level ISA accessors >> to handle the indirection). > > Multi-instance with IO is tricky to do generically because archs already > have all sort of hacks to deal with the fact that inb/outb don't require > an explicit ioremap, so an IO resource can take all sort of shape depending > on the arch. > > Overall it boils down to applying some kind of per-instance "offset" to > the IO port number though. > -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
