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Re: [PATCH for-8.0] hw/rtc/mc146818rtc: Make this rtc device target inde

From: Mark Cave-Ayland
Subject: Re: [PATCH for-8.0] hw/rtc/mc146818rtc: Make this rtc device target independent
Date: Wed, 7 Dec 2022 17:47:48 +0000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.13.0 
On 07/12/2022 16:20, Bernhard Beschow wrote:


Am 7. Dezember 2022 15:29:00 UTC schrieb Mark Cave-Ayland 
<mark.cave-ayland@ilande.co.uk>:

On 06/12/2022 20:06, Thomas Huth wrote:


The only code that is really, really target dependent is the apic-related
code in rtc_policy_slew_deliver_irq(). By moving this code into the hw/i386/
folder (renamed to rtc_apic_policy_slew_deliver_irq()) and passing this
function as parameter to mc146818_rtc_init(), we can make the RTC completely
target-independent.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
   include/hw/rtc/mc146818rtc.h |  7 +++++--
   hw/alpha/dp264.c             |  2 +-
   hw/hppa/machine.c            |  2 +-
   hw/i386/microvm.c            |  3 ++-
   hw/i386/pc.c                 | 10 +++++++++-
   hw/mips/jazz.c               |  2 +-
   hw/ppc/pnv.c                 |  2 +-
   hw/rtc/mc146818rtc.c         | 34 +++++++++++-----------------------
   hw/rtc/meson.build           |  3 +--
   9 files changed, 32 insertions(+), 33 deletions(-)

diff --git a/include/hw/rtc/mc146818rtc.h b/include/hw/rtc/mc146818rtc.h
index 1db0fcee92..c687953cc4 100644
--- a/include/hw/rtc/mc146818rtc.h
+++ b/include/hw/rtc/mc146818rtc.h
@@ -46,14 +46,17 @@ struct RTCState {
       Notifier clock_reset_notifier;
       LostTickPolicy lost_tick_policy;
       Notifier suspend_notifier;
+    bool (*policy_slew_deliver_irq)(RTCState *s);
       QLIST_ENTRY(RTCState) link;
   };
     #define RTC_ISA_IRQ 8
   -ISADevice *mc146818_rtc_init(ISABus *bus, int base_year,
-                             qemu_irq intercept_irq);
+ISADevice *mc146818_rtc_init(ISABus *bus, int base_year, qemu_irq 
intercept_irq,
+                             bool (*policy_slew_deliver_irq)(RTCState *s));
   void rtc_set_memory(ISADevice *dev, int addr, int val);
   int rtc_get_memory(ISADevice *dev, int addr);
+bool rtc_apic_policy_slew_deliver_irq(RTCState *s);
+void qmp_rtc_reset_reinjection(Error **errp);
     #endif /* HW_RTC_MC146818RTC_H */
diff --git a/hw/alpha/dp264.c b/hw/alpha/dp264.c
index c502c8c62a..8723942b52 100644
--- a/hw/alpha/dp264.c
+++ b/hw/alpha/dp264.c
@@ -118,7 +118,7 @@ static void clipper_init(MachineState *machine)
       qdev_connect_gpio_out(i82378_dev, 0, isa_irq);
         /* Since we have an SRM-compatible PALcode, use the SRM epoch.  */
-    mc146818_rtc_init(isa_bus, 1900, rtc_irq);
+    mc146818_rtc_init(isa_bus, 1900, rtc_irq, NULL);
         /* VGA setup.  Don't bother loading the bios.  */
       pci_vga_init(pci_bus);
diff --git a/hw/hppa/machine.c b/hw/hppa/machine.c
index de1cc7ab71..311031714a 100644
--- a/hw/hppa/machine.c
+++ b/hw/hppa/machine.c
@@ -232,7 +232,7 @@ static void machine_hppa_init(MachineState *machine)
       assert(isa_bus);
         /* Realtime clock, used by firmware for PDC_TOD call. */
-    mc146818_rtc_init(isa_bus, 2000, NULL);
+    mc146818_rtc_init(isa_bus, 2000, NULL, NULL);
         /* Serial ports: Lasi and Dino use a 7.272727 MHz clock. */
       serial_mm_init(addr_space, LASI_UART_HPA + 0x800, 0,
diff --git a/hw/i386/microvm.c b/hw/i386/microvm.c
index 170a331e3f..d0ed4dca50 100644
--- a/hw/i386/microvm.c
+++ b/hw/i386/microvm.c
@@ -267,7 +267,8 @@ static void microvm_devices_init(MicrovmMachineState *mms)
         if (mms->rtc == ON_OFF_AUTO_ON ||
           (mms->rtc == ON_OFF_AUTO_AUTO && !kvm_enabled())) {
-        rtc_state = mc146818_rtc_init(isa_bus, 2000, NULL);
+        rtc_state = mc146818_rtc_init(isa_bus, 2000, NULL,
+                                      rtc_apic_policy_slew_deliver_irq);
           microvm_set_rtc(mms, rtc_state);
       }
   diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 546b703cb4..650e7bc199 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -1244,6 +1244,13 @@ static void pc_superio_init(ISABus *isa_bus, bool 
create_fdctrl,
       g_free(a20_line);
   }
   +bool rtc_apic_policy_slew_deliver_irq(RTCState *s)
+{
+    apic_reset_irq_delivered();
+    qemu_irq_raise(s->irq);
+    return apic_get_irq_delivered();
+}
+
   void pc_basic_device_init(struct PCMachineState *pcms,
                             ISABus *isa_bus, qemu_irq *gsi,
                             ISADevice **rtc_state,
@@ -1299,7 +1306,8 @@ void pc_basic_device_init(struct PCMachineState *pcms,
           pit_alt_irq = qdev_get_gpio_in(hpet, HPET_LEGACY_PIT_INT);
           rtc_irq = qdev_get_gpio_in(hpet, HPET_LEGACY_RTC_INT);
       }
-    *rtc_state = mc146818_rtc_init(isa_bus, 2000, rtc_irq);
+    *rtc_state = mc146818_rtc_init(isa_bus, 2000, rtc_irq,
+                                   rtc_apic_policy_slew_deliver_irq);
         qemu_register_boot_set(pc_boot_set, *rtc_state);
   diff --git a/hw/mips/jazz.c b/hw/mips/jazz.c
index 6aefe9a61b..50fbd57b23 100644
--- a/hw/mips/jazz.c
+++ b/hw/mips/jazz.c
@@ -356,7 +356,7 @@ static void mips_jazz_init(MachineState *machine,
       fdctrl_init_sysbus(qdev_get_gpio_in(rc4030, 1), 0x80003000, fds);
         /* Real time clock */
-    mc146818_rtc_init(isa_bus, 1980, NULL);
+    mc146818_rtc_init(isa_bus, 1980, NULL, NULL);
       memory_region_init_io(rtc, NULL, &rtc_ops, NULL, "rtc", 0x1000);
       memory_region_add_subregion(address_space, 0x80004000, rtc);
   diff --git a/hw/ppc/pnv.c b/hw/ppc/pnv.c
index 3d01e26f84..c5482554b7 100644
--- a/hw/ppc/pnv.c
+++ b/hw/ppc/pnv.c
@@ -992,7 +992,7 @@ static void pnv_init(MachineState *machine)
       serial_hds_isa_init(pnv->isa_bus, 0, MAX_ISA_SERIAL_PORTS);
         /* Create an RTC ISA device too */
-    mc146818_rtc_init(pnv->isa_bus, 2000, NULL);
+    mc146818_rtc_init(pnv->isa_bus, 2000, NULL, NULL);
         /*
        * Create the machine BMC simulator and the IPMI BT device for
diff --git a/hw/rtc/mc146818rtc.c b/hw/rtc/mc146818rtc.c
index 1ebb412479..9543ae0279 100644
--- a/hw/rtc/mc146818rtc.c
+++ b/hw/rtc/mc146818rtc.c
@@ -44,11 +44,6 @@
   #include "qapi/visitor.h"
   #include "hw/rtc/mc146818rtc_regs.h"
   -#ifdef TARGET_I386
-#include "qapi/qapi-commands-misc-target.h"
-#include "hw/i386/apic.h"
-#endif
-
   //#define DEBUG_CMOS
   //#define DEBUG_COALESCED
   @@ -112,7 +107,6 @@ static void rtc_coalesced_timer_update(RTCState *s)
   static QLIST_HEAD(, RTCState) rtc_devices =
       QLIST_HEAD_INITIALIZER(rtc_devices);
   -#ifdef TARGET_I386
   void qmp_rtc_reset_reinjection(Error **errp)
   {
       RTCState *s;
@@ -124,9 +118,8 @@ void qmp_rtc_reset_reinjection(Error **errp)
     static bool rtc_policy_slew_deliver_irq(RTCState *s)
   {
-    apic_reset_irq_delivered();
-    qemu_irq_raise(s->irq);
-    return apic_get_irq_delivered();
+    assert(s->policy_slew_deliver_irq);
+    return s->policy_slew_deliver_irq(s);
   }
     static void rtc_coalesced_timer(void *opaque)
@@ -145,13 +138,6 @@ static void rtc_coalesced_timer(void *opaque)
         rtc_coalesced_timer_update(s);
   }
-#else
-static bool rtc_policy_slew_deliver_irq(RTCState *s)
-{
-    assert(0);
-    return false;
-}
-#endif
     static uint32_t rtc_periodic_clock_ticks(RTCState *s)
   {
@@ -922,14 +908,14 @@ static void rtc_realizefn(DeviceState *dev, Error **errp)
       rtc_set_date_from_host(isadev);
         switch (s->lost_tick_policy) {
-#ifdef TARGET_I386
-    case LOST_TICK_POLICY_SLEW:
-        s->coalesced_timer =
-            timer_new_ns(rtc_clock, rtc_coalesced_timer, s);
-        break;
-#endif
       case LOST_TICK_POLICY_DISCARD:
           break;
+    case LOST_TICK_POLICY_SLEW:
+        if (s->policy_slew_deliver_irq) {
+            s->coalesced_timer = timer_new_ns(rtc_clock, rtc_coalesced_timer, 
s);
+            break;
+        }
+        /* fallthrough */
       default:
           error_setg(errp, "Invalid lost tick policy.");
           return;
@@ -960,7 +946,8 @@ static void rtc_realizefn(DeviceState *dev, Error **errp)
       QLIST_INSERT_HEAD(&rtc_devices, s, link);
   }
   -ISADevice *mc146818_rtc_init(ISABus *bus, int base_year, qemu_irq 
intercept_irq)
+ISADevice *mc146818_rtc_init(ISABus *bus, int base_year, qemu_irq 
intercept_irq,
+                             bool (*policy_slew_deliver_irq)(RTCState *s))
   {
       DeviceState *dev;
       ISADevice *isadev;
@@ -969,6 +956,7 @@ ISADevice *mc146818_rtc_init(ISABus *bus, int base_year, 
qemu_irq intercept_irq)
       isadev = isa_new(TYPE_MC146818_RTC);
       dev = DEVICE(isadev);
       s = MC146818_RTC(isadev);
+    s->policy_slew_deliver_irq = policy_slew_deliver_irq;
       qdev_prop_set_int32(dev, "base_year", base_year);
       isa_realize_and_unref(isadev, bus, &error_fatal);
       if (intercept_irq) {
diff --git a/hw/rtc/meson.build b/hw/rtc/meson.build
index dc33973384..34a4d316fa 100644
--- a/hw/rtc/meson.build
+++ b/hw/rtc/meson.build
@@ -13,5 +13,4 @@ softmmu_ss.add(when: 'CONFIG_ASPEED_SOC', if_true: 
files('aspeed_rtc.c'))
   softmmu_ss.add(when: 'CONFIG_GOLDFISH_RTC', if_true: files('goldfish_rtc.c'))
   softmmu_ss.add(when: 'CONFIG_LS7A_RTC', if_true: files('ls7a_rtc.c'))
   softmmu_ss.add(when: 'CONFIG_ALLWINNER_H3', if_true: 
files('allwinner-rtc.c'))
-
-specific_ss.add(when: 'CONFIG_MC146818RTC', if_true: files('mc146818rtc.c'))
+softmmu_ss.add(when: 'CONFIG_MC146818RTC', if_true: files('mc146818rtc.c'))


Ouch this is quite a nasty one :/

These days we really should try and avoid setting function pointers outside of 
_init() and class_init() where possible. If I were looking to model this today 
I'd probably try an approach like this:

- Move apic_irq_delivered into APICCommonState

- Define apic_reset_irq_delivered() and apic_get_irq_delivered() as function 
pointers in APICCommonState and assign them to the current implementations in 
apic_common_initfn() adding an APICCommonState parameter as required

- Grab a reference to APICCommonState in mc146818rtc.c's rtc_realizefn() using either an 
object property link or object_resolve_path_type("", TYPE_APIC_COMMON, NULL)


AFAICS TYPE_APIC_COMMON is x86-specific which doesn't serve the point of the 
patch well ;)
Well you'd have to keep the hw/i386/apic.h include for now, but this approach would move the APIC check from compile time to runtime so the RTC device should still work but without the slew functionality on non-x86 platforms.
This is really following on from the BoF session at KVM forum and the follow-up developers call (see https://lists.gnu.org/archive/html/qemu-devel/2022-11/msg04491.html) where discussions are ongoing about having a single QEMU binary that can attach and wire up any device to an empty machine via the monitor.
In order for this to work the connections between devices needs to be done using QOM and qdev APIs which means that function pointer properties cannot be used. I believe someone (Markus?) went through the remaining function properties and removed them a while back, so we shouldn't be reintroducing them again here. 


- Use "if (s->apic) { .. }" or similar in mc146818rtc.c to guard calling the 
apic_*() functions


IMO mc146818rtc.c shouldn't make any assumptions outside of its scope, 
especially not about any target specifics like an APIC.

I wonder if we could somehow wire up the APIC handling in the x86 IRQ handler.
This may indeed be possible, please do let us know if you have any better ideas. I would add that the good work you've been doing on PIIX3 and PIIX4 means that you've got a much better understanding of how the PC world fits together compared to most people, so if you are interested in this I would definitely encourage you to contribute any ideas you may have and also join the next developers call. 


ATB,

Mark.
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