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

Andre Przywara
2021-02-18T18:28:45Z

On Thu, 18 Feb 2021 13:33:15 +0000
Alexandru Elisei <alexandru.elisei@arm.com> wrote:

> 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.

Yep, will do!

Thanks,
Andre

>
> > +#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;
> > }