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Re: [PATCH v2 03/13] vt82c686: Fix SMBus IO base and configuration regis

From: BALATON Zoltan
Subject: Re: [PATCH v2 03/13] vt82c686: Fix SMBus IO base and configuration registers
Date: Tue, 12 Jan 2021 23:25:53 +0100 (CET)

On Tue, 12 Jan 2021, Jiaxun Yang wrote:
在 2021/1/10 上午4:16, BALATON Zoltan 写道:
The base address of the SMBus io ports and its enabled status is set
by registers in the PCI config space but this was not correctly
emulated. Instead the SMBus registers were mapped on realize to the
base address set by a property to the address expected by fuloong2e

Fix the base and config register handling to more closely model
hardware which allows to remove the property and allows the guest to
control this mapping. Do all this in reset instead of realize so it's
correctly updated on reset.


Thanks for your patch!

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
  hw/isa/vt82c686.c   | 49 +++++++++++++++++++++++++++++++++------------
  hw/mips/fuloong2e.c |  4 +---
  2 files changed, 37 insertions(+), 16 deletions(-)

diff --git a/hw/isa/vt82c686.c b/hw/isa/vt82c686.c
index fe8961b057..9c4d153022 100644
--- a/hw/isa/vt82c686.c
+++ b/hw/isa/vt82c686.c
@@ -22,6 +22,7 @@
  #include "hw/i2c/pm_smbus.h"
  #include "qapi/error.h"
  #include "qemu/module.h"
+#include "qemu/range.h"
  #include "qemu/timer.h"
  #include "exec/address-spaces.h"
  #include "trace.h"
@@ -34,7 +35,6 @@ struct VT686PMState {
      ACPIREGS ar;
      APMState apm;
      PMSMBus smb;
-    uint32_t smb_io_base;
    static void pm_io_space_update(VT686PMState *s)
@@ -50,11 +50,22 @@ static void pm_io_space_update(VT686PMState *s)
  +static void smb_io_space_update(VT686PMState *s)
+    uint32_t smbase = pci_get_long(s->dev.config + 0x90) & 0xfff0UL;
+    memory_region_transaction_begin();
+    memory_region_set_address(&s->smb.io, smbase);
+    memory_region_set_enabled(&s->smb.io, s->dev.config[0xd2] & BIT(0));
+    memory_region_transaction_commit();
  static int vmstate_acpi_post_load(void *opaque, int version_id)
      VT686PMState *s = opaque;
+    smb_io_space_update(s);
      return 0;
  @@ -77,8 +88,18 @@ static const VMStateDescription vmstate_acpi = {
static void pm_write_config(PCIDevice *d, uint32_t addr, uint32_t val, int len)
+    VT686PMState *s = VT82C686B_PM(d);
      trace_via_pm_write(addr, val, len);
      pci_default_write_config(d, addr, val, len);
+    if (ranges_overlap(addr, len, 0x90, 4)) {
+        uint32_t v = pci_get_long(s->dev.config + 0x90);
+        pci_set_long(s->dev.config + 0x90, (v & 0xfff0UL) | 1);

What does this "or 1" do?
The datasheet I found only mentioned the default value of BASE is 0000 0001
but didn't say anything about it's function :-/

It says that in the summary table but later in data sheet there's also detailed description of registers for each part where it says:

Offset 93-90 – SMBus I/O Base ... RW
3-0 Fixed ... always reads 0001b

The above mask and | 1 ensures this. I don't know why lowest bit is always 1 but that seems to be the case for all such regs. Maybe internally these are implemented like PCI BARs where lowest bit means IO space.

+    }
+    if (range_covers_byte(addr, len, 0xd2)) {
+        s->dev.config[0xd2] &= 0xf;
+        smb_io_space_update(s);
+    }
    static void pm_update_sci(VT686PMState *s)
@@ -103,6 +124,17 @@ static void pm_tmr_timer(ACPIREGS *ar)
  +static void vt82c686b_pm_reset(DeviceState *d)
+    VT686PMState *s = VT82C686B_PM(d);
+    /* SMBus IO base */
+    pci_set_long(s->dev.config + 0x90, 1);

Theoretically this kind of magic number should be avoided but
as the rest of the file was written in such style it seems fine for me.

I could add defines for register offsets but did not think that would make it much more readable to have random names instead of random numbers. Likely you'll have to consult the data sheet to find out their meaning anyway.


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