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Re: [PATCH 2/2] via-ide: Also emulate non 100% native mode

From: BALATON Zoltan
Subject: Re: [PATCH 2/2] via-ide: Also emulate non 100% native mode
Date: Sun, 1 Mar 2020 17:31:09 +0100 (CET)
User-agent: Alpine 2.22 (BSF 395 2020-01-19) 
On Sun, 1 Mar 2020, Mark Cave-Ayland wrote:

On 29/02/2020 23:02, BALATON Zoltan wrote:

Some machines operate in "non 100% native mode" where interrupts are
fixed at legacy IDE interrupts and some guests expect this behaviour
without checking based on knowledge about hardware. Even Linux has
arch specific workarounds for this that are activated on such boards
so this needs to be emulated as well.

Signed-off-by: BALATON Zoltan <address@hidden>
---
 hw/ide/via.c            | 60 +++++++++++++++++++++++++++++++++++------
 hw/mips/mips_fulong2e.c |  2 +-
 include/hw/ide.h        |  3 ++-
 3 files changed, 55 insertions(+), 10 deletions(-)

diff --git a/hw/ide/via.c b/hw/ide/via.c
index 096de8dba0..17418c5822 100644
--- a/hw/ide/via.c
+++ b/hw/ide/via.c
@@ -1,9 +1,10 @@
 /*
- * QEMU IDE Emulation: PCI VIA82C686B support.
+ * QEMU VIA southbridge IDE emulation (VT82C686B, VT8231)
  *
  * Copyright (c) 2003 Fabrice Bellard
  * Copyright (c) 2006 Openedhand Ltd.
  * Copyright (c) 2010 Huacai Chen <address@hidden>
+ * Copyright (c) 2019-2020 BALATON Zoltan
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to 
deal
@@ -25,6 +26,8 @@
  */

 #include "qemu/osdep.h"
+#include "qemu/range.h"
+#include "hw/qdev-properties.h"
 #include "hw/pci/pci.h"
 #include "migration/vmstate.h"
 #include "qemu/module.h"
@@ -111,14 +114,43 @@ static void via_ide_set_irq(void *opaque, int n, int 
level)
     } else {
         d->config[0x70 + n * 8] &= ~0x80;
     }
-
     level = (d->config[0x70] & 0x80) || (d->config[0x78] & 0x80);
-    n = pci_get_byte(d->config + PCI_INTERRUPT_LINE);
-    if (n) {
-        qemu_set_irq(isa_get_irq(NULL, n), level);
+
+    /*
+     * Some machines operate in "non 100% native mode" where PCI_INTERRUPT_LINE
+     * is not used but IDE always uses ISA IRQ 14 and 15 even in native mode.
+     * Some guest drivers expect this, often without checking.
+     */
+    if (!(pci_get_byte(d->config + PCI_CLASS_PROG) & (n ? 4 : 1)) ||
+        PCI_IDE(d)->flags & BIT(PCI_IDE_LEGACY_IRQ)) {
+        qemu_set_irq(isa_get_irq(NULL, (n ? 15 : 14)), level);
+    } else {
+        n = pci_get_byte(d->config + PCI_INTERRUPT_LINE);
+        if (n) {
+            qemu_set_irq(isa_get_irq(NULL, n), level);
+        }
     }
 }

+static uint32_t via_ide_config_read(PCIDevice *d, uint32_t address, int len)
+{
+    /*
+     * The pegasos2 firmware writes to PCI_INTERRUPT_LINE but on real
+     * hardware it's fixed at 14 and won't change. Some guests also expect
+     * legacy interrupts, without reading PCI_INTERRUPT_LINE but Linux
+     * depends on this to read 14. We set it to 14 in the reset method and
+     * also set the wmask to 0 to emulate this but that turns out to be not
+     * enough. QEMU resets the PCI bus after this device and
+     * pci_do_device_reset() called from pci_device_reset() will zero
+     * PCI_INTERRUPT_LINE so this config_read function is to counter that and
+     * restore the correct value, otherwise this should not be needed.
+     */
+    if (range_covers_byte(address, len, PCI_INTERRUPT_LINE)) {
+        pci_set_byte(d->config + PCI_INTERRUPT_LINE, 14);
+    }
+    return pci_default_read_config(d, address, len);
+}


This all seems quite strange: so what you're saying is that the VIA is 
programmed
into PCI native mode, but at least on the Pegasos then it should still be 
generating
interrupts on both the PCI bus and the compatibility IRQs?
In my understanding in this "non 100% native mode" IDE interrupts are using only legacy interrupts 14 and 15 even in native mode and PCI interrupts aren't used at all. Linux has this platform specific code: 

https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/arch/powerpc/platforms/chrp/pci.c?h=v4.14.172#n353
which says forcing legacy mode but that's not what actually happens. According to docs in legacy mode (which we don't emulate because we can't switch between legacy and native mode) apart from legacy interrupts the io adresses should also be fixed to legacy IDE ports but what I've seen from firmware and Amiga like OSes on pegasos2 they actually use the controller in "half-native" mode where the io addresses are set with the PCI BARs but the irq is still using 14 and 15. Even in true, 100% native mode a PCI interrupt does not seem to be used but instead the PCI_INTERRUPT_LINE config reg selects one of the ISA interrupts which is then used for both ide channels. On pegasos2 the firmware writes 9 to PCI_INTERRUPT_LINE and without this patch Linux detected that as 100% native mode using IRQ 9 for both channels and worked with that but MorphOS and AmigaOS don't check interrupt config reg and just expect interrupts on 14 and 15 despite using PCI BARs to map io and leaving the mode reg in native mode which the firmware also writes there. So this seems to be a kind of half-native mode in which PCI BARs map io registers but interrupts are locked to legacy interrupts and we need to emulate this for MorphOS and AmigaOS at least. Linux could work both ways if regs are set accordingly but when it says "forcing legacy mode" in above fixup func that just seems to activate other compatibility funcs in 

https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/drivers/ide/setup-pci.c?h=v4.14.172#n484
to know that legacy interrupts should be used instead of the one in config reg but PCI BARs are still mapped and io is accessed at those addresses which would not make sense in true legacy mode.
I've also got register dumps from a real Pegasos2 which shows PCI_INTERRUPT_LINE set to 14 after booting Linux even if firmware tries to change that to 9 so I think it's fixed on real hardware and guests work if we emulate that in this patch so I think this confirms this matches real hardware at least more or less.
This patch fixes interrupt line to 14 but that's not a problem at least for Linux or anything that checks the config reg contents, the only difference is that without legacy-irq set it will use IRQ 14 for both IDE channels that seems to work with the mips_fulong2e which is the only other board using via-ide.
All of the above is true for via-ide and the two boards we emulate, I don't know if this applies to CMD646 or that conroller and boards using it have different quirks. Also via-ide is part of a southbridge chip (or several similar southbridges) where connetctions within the chip to IRQs may be peculiar while CMD646 may be a more normal PCI device. 

Regards,
BALATON Zoltan




 static void via_ide_reset(DeviceState *dev)
 {
     PCIIDEState *d = PCI_IDE(dev);
@@ -169,7 +201,8 @@ static void via_ide_realize(PCIDevice *dev, Error **errp)

     pci_config_set_prog_interface(pci_conf, 0x8f); /* native PCI ATA mode */
     pci_set_long(pci_conf + PCI_CAPABILITY_LIST, 0x000000c0);
-    dev->wmask[PCI_INTERRUPT_LINE] = 0xf;
+    dev->wmask[PCI_CLASS_PROG] = 5;
+    dev->wmask[PCI_INTERRUPT_LINE] = 0;

     memory_region_init_io(&d->data_bar[0], OBJECT(d), &pci_ide_data_le_ops,
                           &d->bus[0], "via-ide0-data", 8);
@@ -213,14 +246,23 @@ static void via_ide_exitfn(PCIDevice *dev)
     }
 }

-void via_ide_init(PCIBus *bus, DriveInfo **hd_table, int devfn)
+void via_ide_init(PCIBus *bus, DriveInfo **hd_table, int devfn,
+                  bool legacy_irq)
 {
     PCIDevice *dev;

-    dev = pci_create_simple(bus, devfn, "via-ide");
+    dev = pci_create(bus, devfn, "via-ide");
+    qdev_prop_set_bit(&dev->qdev, "legacy-irq", legacy_irq);
+    qdev_init_nofail(&dev->qdev);
     pci_ide_create_devs(dev, hd_table);
 }

+static Property via_ide_properties[] = {
+    DEFINE_PROP_BIT("legacy-irq", PCIIDEState, flags, PCI_IDE_LEGACY_IRQ,
+                    false),
+    DEFINE_PROP_END_OF_LIST(),
+};
+
 static void via_ide_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
@@ -229,10 +271,12 @@ static void via_ide_class_init(ObjectClass *klass, void 
*data)
     dc->reset = via_ide_reset;
     k->realize = via_ide_realize;
     k->exit = via_ide_exitfn;
+    k->config_read = via_ide_config_read;
     k->vendor_id = PCI_VENDOR_ID_VIA;
     k->device_id = PCI_DEVICE_ID_VIA_IDE;
     k->revision = 0x06;
     k->class_id = PCI_CLASS_STORAGE_IDE;
+    device_class_set_props(dc, via_ide_properties);
     set_bit(DEVICE_CATEGORY_STORAGE, dc->categories);
 }

diff --git a/hw/mips/mips_fulong2e.c b/hw/mips/mips_fulong2e.c
index 4727b1d3a4..150182c62a 100644
--- a/hw/mips/mips_fulong2e.c
+++ b/hw/mips/mips_fulong2e.c
@@ -257,7 +257,7 @@ static void vt82c686b_southbridge_init(PCIBus *pci_bus, int 
slot, qemu_irq intc,
     isa_create_simple(isa_bus, TYPE_VT82C686B_SUPERIO);

     ide_drive_get(hd, ARRAY_SIZE(hd));
-    via_ide_init(pci_bus, hd, PCI_DEVFN(slot, 1));
+    via_ide_init(pci_bus, hd, PCI_DEVFN(slot, 1), false);

     pci_create_simple(pci_bus, PCI_DEVFN(slot, 2), "vt82c686b-usb-uhci");
     pci_create_simple(pci_bus, PCI_DEVFN(slot, 3), "vt82c686b-usb-uhci");
diff --git a/include/hw/ide.h b/include/hw/ide.h
index d88c5ee695..2a7001ccba 100644
--- a/include/hw/ide.h
+++ b/include/hw/ide.h
@@ -18,7 +18,8 @@ PCIDevice *pci_piix3_xen_ide_init(PCIBus *bus, DriveInfo 
**hd_table, int devfn);
 PCIDevice *pci_piix3_ide_init(PCIBus *bus, DriveInfo **hd_table, int devfn);
 PCIDevice *pci_piix4_ide_init(PCIBus *bus, DriveInfo **hd_table, int devfn);
 int pci_piix3_xen_ide_unplug(DeviceState *dev, bool aux);
-void via_ide_init(PCIBus *bus, DriveInfo **hd_table, int devfn);
+void via_ide_init(PCIBus *bus, DriveInfo **hd_table, int devfn,
+                  bool legacy_irq);

 /* ide-mmio.c */
 void mmio_ide_init_drives(DeviceState *dev, DriveInfo *hd0, DriveInfo *hd1);


ATB,

Mark.
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