Re: [PATCH kvmtool 21/21] hw/rtc: ARM/arm64: Use MMIO at higher addresses

Alexandru Elisei
2021-02-18T16:13:56Z

Hi Andre,

On 12/10/20 2:29 PM, Andre Przywara wrote:
> Using the RTC device at its legacy I/O address as set by IBM in 1981
> was a kludge we used for simplicity on ARM platforms as well.
> However this imposes problems due to their missing alignment and overlap
> with the PCI I/O address space.
>
> Now that we can switch a device easily between using ioports and
> MMIO, let's move the RTC out of the first 4K of memory on ARM platforms.
>
> That should be transparent for well behaved guests, since the change is
> naturally reflected in the device tree.
>
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> ---
> hw/rtc.c | 24 ++++++++++++++++--------
> 1 file changed, 16 insertions(+), 8 deletions(-)
>
> diff --git a/hw/rtc.c b/hw/rtc.c
> index ee4c9102..bdb88f0f 100644
> --- a/hw/rtc.c
> +++ b/hw/rtc.c
> @@ -5,6 +5,15 @@
>
> #include <time.h>
>
> +#if defined(CONFIG_ARM) || defined(CONFIG_ARM64)
> +#define RTC_BUS_TYPE DEVICE_BUS_MMIO
> +#define RTC_BASE_ADDRESS 0x1010000

This looks correct, the base address is the serial base address + 64k, so they
don't overlap, and it doesn't overlap with the flash memory either. Same comment
as for the serial, I think the reason for choosing this address should be
mentioned, and the region should be put in the arch memory layout file. Other than
that, the patch looks good.

Thanks,

Alex

> +#else
> +/* PORT 0070-007F - CMOS RAM/RTC (REAL TIME CLOCK) */
> +#define RTC_BUS_TYPE DEVICE_BUS_IOPORT
> +#define RTC_BASE_ADDRESS 0x70
> +#endif
> +
> /*
> * MC146818 RTC registers
> */
> @@ -49,7 +58,7 @@ static void cmos_ram_io(struct kvm_cpu *vcpu, u64 addr, u8 *data,
> time_t ti;
>
> if (is_write) {
> - if (addr == 0x70) { /* index register */
> + if (addr == RTC_BASE_ADDRESS) { /* index register */
> u8 value = ioport__read8(data);
>
> vcpu->kvm->nmi_disabled = value & (1UL << 7);
> @@ -70,7 +79,7 @@ static void cmos_ram_io(struct kvm_cpu *vcpu, u64 addr, u8 *data,
> return;
> }
>
> - if (addr == 0x70)
> + if (addr == RTC_BASE_ADDRESS) /* index register is write-only */
> return;
>
> time(&ti);
> @@ -127,7 +136,7 @@ static void generate_rtc_fdt_node(void *fdt,
> u8 irq,
> enum irq_type))
> {
> - u64 reg_prop[2] = { cpu_to_fdt64(0x70), cpu_to_fdt64(2) };
> + u64 reg_prop[2] = { cpu_to_fdt64(RTC_BASE_ADDRESS), cpu_to_fdt64(2) };
>
> _FDT(fdt_begin_node(fdt, "rtc"));
> _FDT(fdt_property_string(fdt, "compatible", "motorola,mc146818"));
> @@ -139,7 +148,7 @@ static void generate_rtc_fdt_node(void *fdt,
> #endif
>
> struct device_header rtc_dev_hdr = {
> - .bus_type = DEVICE_BUS_IOPORT,
> + .bus_type = RTC_BUS_TYPE,
> .data = generate_rtc_fdt_node,
> };
>
> @@ -151,8 +160,8 @@ int rtc__init(struct kvm *kvm)
> if (r < 0)
> return r;
>
> - /* PORT 0070-007F - CMOS RAM/RTC (REAL TIME CLOCK) */
> - r = kvm__register_pio(kvm, 0x0070, 2, cmos_ram_io, NULL);
> + r = kvm__register_iotrap(kvm, RTC_BASE_ADDRESS, 2, cmos_ram_io, NULL,
> + RTC_BUS_TYPE);
> if (r < 0)
> goto out_device;
>
> @@ -170,8 +179,7 @@ dev_init(rtc__init);
>
> int rtc__exit(struct kvm *kvm)
> {
> - /* PORT 0070-007F - CMOS RAM/RTC (REAL TIME CLOCK) */
> - kvm__deregister_pio(kvm, 0x0070);
> + kvm__deregister_iotrap(kvm, RTC_BASE_ADDRESS, RTC_BUS_TYPE);
>
> return 0;
> }