On 10/29/2014 12:43 AM, Arnd Bergmann wrote: > On Tuesday 28 October 2014 20:58:48 Kevin Cernekee wrote: >> >> +#ifdef CONFIG_RAW_IRQ_ACCESSORS >> + >> +#ifndef irq_reg_writel >> +# define irq_reg_writel(val, addr) __raw_writel(val, addr) >> +#endif >> +#ifndef irq_reg_readl >> +# define irq_reg_readl(addr) __raw_readl(addr) >> +#endif >> + >> +#else >> + > > No, this is just wrong: registers almost always have a fixed endianess > indenpent of CPU endianess, so if you use __raw_writel, it will be > broken on one or the other. Our brcmstb platforms had an endian strap settings for MIPS-based platforms, and for most peripherals this would be just completely transparent, as the HW always will do the internal swapping, such that host CPU does read/writes in its native endianess regardless of the actual strap settings. AFAICT bcm3384, a MIPS-based Cable Modem platform has only one endianess setting: BE, and the HW only supports that specific endianess. > > If you have a machine that uses big-endian registers in the interrupt > controller, you need to find a way to use the correct accessors > (e.g. iowrite32be) and use them independent of what endianess the CPU > is running. > > As this code is being used on all sorts of platforms, you can't assume > that they all use the same endianess, which makes it rather tricky. I think the more general problem with the use of readl_*() I/O accessors is that they just happen to work fine on most platforms out there: ARM Little-endian, because this nicely matches the endianess expected by the HW and that does not enforce an audit of whether your actual peripheral expects little-endian writes to be done. The other problem is that readl() on ARM implies a barrier, which is not necesarily true/necessary for some other platforms such as some MIPS processors. > > As the first step, you can probably introduce a new Kconfig symbol > GENERIC_IRQ_CHIP_BE, and then make that mutually exclusive with the > existing users that all use little-endian registers: > > #if defined(CONFIG_GENERIC_IRQ_CHIP) && !defined(CONFIG_GENERIC_IRQ_CHIP_BE) > #define irq_reg_writel(val, addr) writel(val, addr) > #else if defined(CONFIG_GENERIC_IRQ_CHIP_BE) && !defined(CONFIG_GENERIC_IRQ_CHIP) > #define irq_reg_writel(val, addr) iowrite32be(val, addr) > #else > /* provoke a compile error when this is used */ > #define irq_reg_writel(val, addr) irq_reg_writel_unknown_endian(val, addr) > #endif > > and > > --- a/kernel/irq/Makefile > +++ b/kernel/irq/Makefile > @@ -1,5 +1,6 @@ > > obj-y := irqdesc.o handle.o manage.o spurious.o resend.o chip.o dummychip.o devres.o > +obj-$(CONFIG_GENERIC_IRQ_CHIP_BE) += generic-chip.o > obj-$(CONFIG_GENERIC_IRQ_CHIP) += generic-chip.o > obj-$(CONFIG_GENERIC_IRQ_PROBE) += autoprobe.o > obj-$(CONFIG_IRQ_DOMAIN) += irqdomain.o > > Note that you might also have a case where you have more than > one generic irqchip driver built into the kernel, which require > different endianess. We can't really support that case without > changing the generic-chip implementation. > > Arnd > -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
