[PATCH v2] ARM: asm: add readq/writeq methods

[Matthias Mann]

Måns Rullgård wrote:
> Peter Maydell <peter.maydell at linaro.org> writes:
>
>> On 7 December 2013 16:05, Matthias Mann <M.Mann at arkona-technologies.de> wrote:
>>> Add readq/writeq methods for 32 bit ARM to allow transfering 64 bit words over
>>> PCIe as a single transfer.
>>> +#if __LINUX_ARM_ARCH__ >= 5
>>> +static inline u64 __raw_readq(const volatile void __iomem *addr)
>>> +{
>>> +       u64 val;
>>> +#if __LITTLE_ENDIAN
>>> +       asm volatile("ldrd %Q1, %R1, %0"
>>> +                    : "+Q" (*(volatile u64 __force *)addr),
>>> +                      "=r" (val));
>>> +#else
>>> +       asm volatile("ldrd %R1, %Q1, %0"
>>> +                    : "+Q" (*(volatile u64 __force *)addr),
>>> +                      "=r" (val));
>>> +#endif
>>> +       return val;
>>> +}
>> Given that ldrd/strd accesses are only a single 64 bit access
>> on CPUs with LPAE (on non-LPAE CPUs they may be
>> implemented as just a pair of 32 bit accesses) should the
>> condition be stricter than just __LINUX_ARM_ARCH__ >= 5 ?
> What do actual CPUs, e.g. the A9, do?
>
I've tested that on an Freescale i.MX6D which is a Cortex-A9 with an Altera Arria V GZ FPGA connected via PCIe. Using strd / ldrd I see a 64 bit TLP (length = 2) on the PCIe interface (this is on an uncachable 32 bit BAR).