[Qemu-devel] [PATCH] i386: drop FDC in pc-q35-2.4+ if neither it nor floppy drives are wanted

[Laszlo Ersek <lersek@redhat.com>]

It is Very annoying to carry forward an outdatEd coNtroller with a mOdern
Machine type.

Hence, let us not instantiate the FDC when all of the following apply:
- the machine type is pc-q35-2.4 or later,
- "-device isa-fdc" is not passed on the command line (nor in the config
  file),
- no "-drive if=floppy,..." is requested.

The first part of the code flow, updated by the patch, is as follows:

1. The "no_floppy = 1" machine class setting causes "default_floppy" in
   main() to become zero.

2. Hence default_drive() will not call drive_add() and drive_new() for
   IF_FLOPPY, index=0.

This alone would not suffice, because the pc_basic_device_init() function
creates the FDC regardless of actual floppy drives. Therefore,

3. pc_basic_device_init() should only create the FDC if that's desirable
   for the platform (= all PIIX types, and Q35 types earlier than 2.4),
   *or* the user requested at least one IF_FLOPPY drive.

4. If the FDC is not created, callers of pc_basic_device_init() --
   pc_q35_init() and pc_init1() -- will pass floppy=NULL to
   pc_cmos_init(). Luckily, pc_cmos_init() already handles that case.

I verified the patch under the following scenarios, with "info qtree" and
with the MAP command of the UEFI shell (in OVMF):
- "pc" machine type -- no changes, FDC present,
- "pc-q35-2.3" machine type -- no changes, FDC present,
- "pc-q35" machine type with "-device isa-fdc" -- no changes, FDC present,
- "pc-q35" machine type with "-drive if=floppy,..." -- no changes, FDC
  present,
- "pc-q35" -- no FDC.

Suggested-by: Markus Armbruster <armbru@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
---
 include/hw/i386/pc.h |  1 +
 hw/i386/pc.c         |  4 +++-
 hw/i386/pc_piix.c    |  2 +-
 hw/i386/pc_q35.c     | 12 +++++++++---
 4 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
index 1b35168..55522b7 100644
--- a/include/hw/i386/pc.h
+++ b/include/hw/i386/pc.h
@@ -199,6 +199,7 @@ qemu_irq *pc_allocate_cpu_irq(void);
 DeviceState *pc_vga_init(ISABus *isa_bus, PCIBus *pci_bus);
 void pc_basic_device_init(ISABus *isa_bus, qemu_irq *gsi,
                           ISADevice **rtc_state,
+                          bool force_fdctrl,
                           ISADevice **floppy,
                           bool no_vmport,
                           uint32 hpet_irqs);
diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 769eb25..b77d9b4 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -1395,6 +1395,7 @@ static const MemoryRegionOps ioportF0_io_ops = {
 
 void pc_basic_device_init(ISABus *isa_bus, qemu_irq *gsi,
                           ISADevice **rtc_state,
+                          bool force_fdctrl,
                           ISADevice **floppy,
                           bool no_vmport,
                           uint32 hpet_irqs)
@@ -1489,8 +1490,9 @@ void pc_basic_device_init(ISABus *isa_bus, qemu_irq *gsi,
 
     for(i = 0; i < MAX_FD; i++) {
         fd[i] = drive_get(IF_FLOPPY, 0, i);
+        force_fdctrl |= !!fd[i];
     }
-    *floppy = fdctrl_init_isa(isa_bus, fd);
+    *floppy = force_fdctrl ? fdctrl_init_isa(isa_bus, fd) : NULL;
 }
 
 void pc_nic_init(ISABus *isa_bus, PCIBus *pci_bus)
diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index 212e263..9f530c4 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -242,7 +242,7 @@ static void pc_init1(MachineState *machine,
     }
 
     /* init basic PC hardware */
-    pc_basic_device_init(isa_bus, gsi, &rtc_state, &floppy,
+    pc_basic_device_init(isa_bus, gsi, &rtc_state, true, &floppy,
                          (pc_machine->vmport != ON_OFF_AUTO_ON), 0x4);
 
     pc_nic_init(isa_bus, pci_bus);
diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index e67f2de..4d68340 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -60,6 +60,7 @@ static bool smbios_uuid_encoded = true;
  */
 static bool gigabyte_align = true;
 static bool has_reserved_memory = true;
+static bool force_fdctrl;
 
 /* PC hardware initialisation */
 static void pc_q35_init(MachineState *machine)
@@ -250,7 +251,7 @@ static void pc_q35_init(MachineState *machine)
     }
 
     /* init basic PC hardware */
-    pc_basic_device_init(isa_bus, gsi, &rtc_state, &floppy,
+    pc_basic_device_init(isa_bus, gsi, &rtc_state, force_fdctrl, &floppy,
                          (pc_machine->vmport != ON_OFF_AUTO_ON), 0xff0104);
 
     /* connect pm stuff to lpc */
@@ -291,6 +292,7 @@ static void pc_q35_init(MachineState *machine)
 
 static void pc_compat_2_3(MachineState *machine)
 {
+    force_fdctrl = true;
 }
 
 static void pc_compat_2_2(MachineState *machine)
@@ -424,7 +426,8 @@ static void pc_q35_init_1_4(MachineState *machine)
 #define PC_Q35_2_4_MACHINE_OPTIONS                      \
     PC_Q35_MACHINE_OPTIONS,                             \
     .default_machine_opts = "firmware=bios-256k.bin",   \
-    .default_display = "std"
+    .default_display = "std",                           \
+    .no_floppy = 1
 
 static QEMUMachine pc_q35_machine_v2_4 = {
     PC_Q35_2_4_MACHINE_OPTIONS,
@@ -433,7 +436,10 @@ static QEMUMachine pc_q35_machine_v2_4 = {
     .init = pc_q35_init,
 };
 
-#define PC_Q35_2_3_MACHINE_OPTIONS PC_Q35_2_4_MACHINE_OPTIONS
+#define PC_Q35_2_3_MACHINE_OPTIONS                      \
+    PC_Q35_MACHINE_OPTIONS,                             \
+    .default_machine_opts = "firmware=bios-256k.bin",   \
+    .default_display = "std"
 
 static QEMUMachine pc_q35_machine_v2_3 = {
     PC_Q35_2_3_MACHINE_OPTIONS,
-- 
1.8.3.1