diff mbox

[v2,2/3] hw/i386/pc: reflect any FDC @ ioport 0x3f0 in the CMOS

Message ID 1435239307-13369-3-git-send-email-lersek@redhat.com
State New
Headers show

Commit Message

Laszlo Ersek June 25, 2015, 1:35 p.m. UTC 
With the pc-q35-2.4 machine type, if the user creates an ISA FDC manually:

  -device isa-fdc,driveA=drive-fdc0-0-0 \
  -drive file=...,if=none,id=drive-fdc0-0-0,format=raw

then the board-default FDC will be skipped, and only the explicitly
requested FDC will exist. qtree-wise, this is correct; however such an FDC
is currently not registered in the CMOS, because that code is only reached
for the board-default FDC.

The pc_cmos_init_late() one-shot reset handler -- one-shot because the
CMOS is not reprogrammed during warm reset -- should search for any ISA
FDC devices, created implicitly (by board code) or explicitly, and set the
CMOS accordingly to the ISA FDC(s) with iobase=0x3f0:

- if there is no such FDC, report both drives absent,
- if there is exactly one such FDC, report its drives in the CMOS,
- if there are more than one such FDCs, then pick one (it is not specified
  which one), and print a warning about the ambiguity.

Cc: Jan Tomko <jtomko@redhat.com>
Cc: John Snow <jsnow@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Reported-by: Jan Tomko <jtomko@redhat.com>
Suggested-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
---

Notes:
    v2:
    
    - coding style updates:
    
      - replace (iobase != 0x3f0) with (local_err || iobase != 0x3f0)
        [Markus]
    
      - replace container_path, assigned from a compound literal, with a
        more traditional file scope array called "fdc_container_path";
        employ ARRAY_SIZE()-based loop [Markus]
    
    - consequently, checkpatch complains no more; drop Blue Swirl from Cc
    
    - picked up John's R-b, asking for Markus's anew
    
    v1:
    
    - Look for ISA FDC with iobase=0x3f0, not distinguishing the board
      default ISA FDC at all [Markus]. Handling the board-default ISA FDC
      uniformly requires scanning the "/unattached" container.
    
    - Checkpatch barfs at this patch (it doesn't recognize the compound
      literal (const char *[]) { ... }). I didn't care; this pattern is
      widely used in the tree. Just run
    
      git grep -F '*[])'
    
      CC'd Blue Swirl for this reason.

 hw/i386/pc.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 55 insertions(+), 2 deletions(-)

Comments

Markus Armbruster June 26, 2015, 9:31 a.m. UTC | #1 
Laszlo Ersek <lersek@redhat.com> writes:

> With the pc-q35-2.4 machine type, if the user creates an ISA FDC manually:
>
>   -device isa-fdc,driveA=drive-fdc0-0-0 \
>   -drive file=...,if=none,id=drive-fdc0-0-0,format=raw
>
> then the board-default FDC will be skipped, and only the explicitly
> requested FDC will exist. qtree-wise, this is correct; however such an FDC
> is currently not registered in the CMOS, because that code is only reached
> for the board-default FDC.
>
> The pc_cmos_init_late() one-shot reset handler -- one-shot because the
> CMOS is not reprogrammed during warm reset -- should search for any ISA
> FDC devices, created implicitly (by board code) or explicitly, and set the
> CMOS accordingly to the ISA FDC(s) with iobase=0x3f0:
>
> - if there is no such FDC, report both drives absent,
> - if there is exactly one such FDC, report its drives in the CMOS,
> - if there are more than one such FDCs, then pick one (it is not specified
>   which one), and print a warning about the ambiguity.
>
> Cc: Jan Tomko <jtomko@redhat.com>
> Cc: John Snow <jsnow@redhat.com>
> Cc: Markus Armbruster <armbru@redhat.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Reported-by: Jan Tomko <jtomko@redhat.com>
> Suggested-by: Markus Armbruster <armbru@redhat.com>
> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
> Reviewed-by: John Snow <jsnow@redhat.com>

Reviewed-by: Markus Armbruster <armbru@redhat.com>
Laszlo Ersek June 26, 2015, 12:25 p.m. UTC | #2 
On 06/26/15 11:31, Markus Armbruster wrote:
> Laszlo Ersek <lersek@redhat.com> writes:
> 
>> With the pc-q35-2.4 machine type, if the user creates an ISA FDC manually:
>>
>>   -device isa-fdc,driveA=drive-fdc0-0-0 \
>>   -drive file=...,if=none,id=drive-fdc0-0-0,format=raw
>>
>> then the board-default FDC will be skipped, and only the explicitly
>> requested FDC will exist. qtree-wise, this is correct; however such an FDC
>> is currently not registered in the CMOS, because that code is only reached
>> for the board-default FDC.
>>
>> The pc_cmos_init_late() one-shot reset handler -- one-shot because the
>> CMOS is not reprogrammed during warm reset -- should search for any ISA
>> FDC devices, created implicitly (by board code) or explicitly, and set the
>> CMOS accordingly to the ISA FDC(s) with iobase=0x3f0:
>>
>> - if there is no such FDC, report both drives absent,
>> - if there is exactly one such FDC, report its drives in the CMOS,
>> - if there are more than one such FDCs, then pick one (it is not specified
>>   which one), and print a warning about the ambiguity.
>>
>> Cc: Jan Tomko <jtomko@redhat.com>
>> Cc: John Snow <jsnow@redhat.com>
>> Cc: Markus Armbruster <armbru@redhat.com>
>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> Reported-by: Jan Tomko <jtomko@redhat.com>
>> Suggested-by: Markus Armbruster <armbru@redhat.com>
>> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
>> Reviewed-by: John Snow <jsnow@redhat.com>
> 
> Reviewed-by: Markus Armbruster <armbru@redhat.com>

Thank you. Can you or John please send a PULL req for this? (Or include
it in an upcoming PULL of yours.)

I've been Cc'ing Paolo because the get-maintainer script reported him at
the top for the patch set, but I believe he might not have time for this
now.

Thanks!
Laszlo
John Snow June 26, 2015, 6:50 p.m. UTC | #3 
On 06/26/2015 08:25 AM, Laszlo Ersek wrote:
> On 06/26/15 11:31, Markus Armbruster wrote:
>> Laszlo Ersek <lersek@redhat.com> writes:
>>
>>> With the pc-q35-2.4 machine type, if the user creates an ISA FDC manually:
>>>
>>>   -device isa-fdc,driveA=drive-fdc0-0-0 \
>>>   -drive file=...,if=none,id=drive-fdc0-0-0,format=raw
>>>
>>> then the board-default FDC will be skipped, and only the explicitly
>>> requested FDC will exist. qtree-wise, this is correct; however such an FDC
>>> is currently not registered in the CMOS, because that code is only reached
>>> for the board-default FDC.
>>>
>>> The pc_cmos_init_late() one-shot reset handler -- one-shot because the
>>> CMOS is not reprogrammed during warm reset -- should search for any ISA
>>> FDC devices, created implicitly (by board code) or explicitly, and set the
>>> CMOS accordingly to the ISA FDC(s) with iobase=0x3f0:
>>>
>>> - if there is no such FDC, report both drives absent,
>>> - if there is exactly one such FDC, report its drives in the CMOS,
>>> - if there are more than one such FDCs, then pick one (it is not specified
>>>   which one), and print a warning about the ambiguity.
>>>
>>> Cc: Jan Tomko <jtomko@redhat.com>
>>> Cc: John Snow <jsnow@redhat.com>
>>> Cc: Markus Armbruster <armbru@redhat.com>
>>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>>> Reported-by: Jan Tomko <jtomko@redhat.com>
>>> Suggested-by: Markus Armbruster <armbru@redhat.com>
>>> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
>>> Reviewed-by: John Snow <jsnow@redhat.com>
>>
>> Reviewed-by: Markus Armbruster <armbru@redhat.com>
> 
> Thank you. Can you or John please send a PULL req for this? (Or include
> it in an upcoming PULL of yours.)
> 
> I've been Cc'ing Paolo because the get-maintainer script reported him at
> the top for the patch set, but I believe he might not have time for this
> now.
> 
> Thanks!
> Laszlo
> 

This is technically out-of-tree for me, because it's touching init
instead of my device.

Best guess is Eduardo Habkost, whom I have CC'd.
Eduardo Habkost June 26, 2015, 7:09 p.m. UTC | #4 
On Fri, Jun 26, 2015 at 02:50:04PM -0400, John Snow wrote:
> On 06/26/2015 08:25 AM, Laszlo Ersek wrote:
> > On 06/26/15 11:31, Markus Armbruster wrote:
> >> Laszlo Ersek <lersek@redhat.com> writes:
> >>
> >>> With the pc-q35-2.4 machine type, if the user creates an ISA FDC manually:
> >>>
> >>>   -device isa-fdc,driveA=drive-fdc0-0-0 \
> >>>   -drive file=...,if=none,id=drive-fdc0-0-0,format=raw
> >>>
> >>> then the board-default FDC will be skipped, and only the explicitly
> >>> requested FDC will exist. qtree-wise, this is correct; however such an FDC
> >>> is currently not registered in the CMOS, because that code is only reached
> >>> for the board-default FDC.
> >>>
> >>> The pc_cmos_init_late() one-shot reset handler -- one-shot because the
> >>> CMOS is not reprogrammed during warm reset -- should search for any ISA
> >>> FDC devices, created implicitly (by board code) or explicitly, and set the
> >>> CMOS accordingly to the ISA FDC(s) with iobase=0x3f0:
> >>>
> >>> - if there is no such FDC, report both drives absent,
> >>> - if there is exactly one such FDC, report its drives in the CMOS,
> >>> - if there are more than one such FDCs, then pick one (it is not specified
> >>>   which one), and print a warning about the ambiguity.
> >>>
> >>> Cc: Jan Tomko <jtomko@redhat.com>
> >>> Cc: John Snow <jsnow@redhat.com>
> >>> Cc: Markus Armbruster <armbru@redhat.com>
> >>> Cc: Paolo Bonzini <pbonzini@redhat.com>
> >>> Reported-by: Jan Tomko <jtomko@redhat.com>
> >>> Suggested-by: Markus Armbruster <armbru@redhat.com>
> >>> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
> >>> Reviewed-by: John Snow <jsnow@redhat.com>
> >>
> >> Reviewed-by: Markus Armbruster <armbru@redhat.com>
> > 
> > Thank you. Can you or John please send a PULL req for this? (Or include
> > it in an upcoming PULL of yours.)
> > 
> > I've been Cc'ing Paolo because the get-maintainer script reported him at
> > the top for the patch set, but I believe he might not have time for this
> > now.
> > 
> > Thanks!
> > Laszlo
> > 
> 
> This is technically out-of-tree for me, because it's touching init
> instead of my device.
> 
> Best guess is Eduardo Habkost, whom I have CC'd.

Michael is the PC maintainer.
Markus Armbruster June 29, 2015, 9:33 a.m. UTC | #5 
Eduardo Habkost <ehabkost@redhat.com> writes:

> On Fri, Jun 26, 2015 at 02:50:04PM -0400, John Snow wrote:
>> On 06/26/2015 08:25 AM, Laszlo Ersek wrote:
>> > On 06/26/15 11:31, Markus Armbruster wrote:
>> >> Laszlo Ersek <lersek@redhat.com> writes:
>> >>
>> >>> With the pc-q35-2.4 machine type, if the user creates an ISA FDC manually:
>> >>>
>> >>>   -device isa-fdc,driveA=drive-fdc0-0-0 \
>> >>>   -drive file=...,if=none,id=drive-fdc0-0-0,format=raw
>> >>>
>> >>> then the board-default FDC will be skipped, and only the explicitly
>> >>> requested FDC will exist. qtree-wise, this is correct; however such an FDC
>> >>> is currently not registered in the CMOS, because that code is only reached
>> >>> for the board-default FDC.
>> >>>
>> >>> The pc_cmos_init_late() one-shot reset handler -- one-shot because the
>> >>> CMOS is not reprogrammed during warm reset -- should search for any ISA
>> >>> FDC devices, created implicitly (by board code) or explicitly, and set the
>> >>> CMOS accordingly to the ISA FDC(s) with iobase=0x3f0:
>> >>>
>> >>> - if there is no such FDC, report both drives absent,
>> >>> - if there is exactly one such FDC, report its drives in the CMOS,
>> >>> - if there are more than one such FDCs, then pick one (it is not specified
>> >>>   which one), and print a warning about the ambiguity.
>> >>>
>> >>> Cc: Jan Tomko <jtomko@redhat.com>
>> >>> Cc: John Snow <jsnow@redhat.com>
>> >>> Cc: Markus Armbruster <armbru@redhat.com>
>> >>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> >>> Reported-by: Jan Tomko <jtomko@redhat.com>
>> >>> Suggested-by: Markus Armbruster <armbru@redhat.com>
>> >>> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
>> >>> Reviewed-by: John Snow <jsnow@redhat.com>
>> >>
>> >> Reviewed-by: Markus Armbruster <armbru@redhat.com>
>> > 
>> > Thank you. Can you or John please send a PULL req for this? (Or include
>> > it in an upcoming PULL of yours.)
>> > 
>> > I've been Cc'ing Paolo because the get-maintainer script reported him at
>> > the top for the patch set, but I believe he might not have time for this
>> > now.
>> > 
>> > Thanks!
>> > Laszlo
>> > 
>> 
>> This is technically out-of-tree for me, because it's touching init
>> instead of my device.
>> 
>> Best guess is Eduardo Habkost, whom I have CC'd.
>
> Michael is the PC maintainer.

Michael, we really needs this series in 2.4, because without it floppy
is broken for Q35.
Michael S. Tsirkin June 29, 2015, 9:55 a.m. UTC | #6 
On Fri, Jun 26, 2015 at 02:25:42PM +0200, Laszlo Ersek wrote:
> On 06/26/15 11:31, Markus Armbruster wrote:
> > Laszlo Ersek <lersek@redhat.com> writes:
> > 
> >> With the pc-q35-2.4 machine type, if the user creates an ISA FDC manually:
> >>
> >>   -device isa-fdc,driveA=drive-fdc0-0-0 \
> >>   -drive file=...,if=none,id=drive-fdc0-0-0,format=raw
> >>
> >> then the board-default FDC will be skipped, and only the explicitly
> >> requested FDC will exist. qtree-wise, this is correct; however such an FDC
> >> is currently not registered in the CMOS, because that code is only reached
> >> for the board-default FDC.
> >>
> >> The pc_cmos_init_late() one-shot reset handler -- one-shot because the
> >> CMOS is not reprogrammed during warm reset -- should search for any ISA
> >> FDC devices, created implicitly (by board code) or explicitly, and set the
> >> CMOS accordingly to the ISA FDC(s) with iobase=0x3f0:
> >>
> >> - if there is no such FDC, report both drives absent,
> >> - if there is exactly one such FDC, report its drives in the CMOS,
> >> - if there are more than one such FDCs, then pick one (it is not specified
> >>   which one), and print a warning about the ambiguity.
> >>
> >> Cc: Jan Tomko <jtomko@redhat.com>
> >> Cc: John Snow <jsnow@redhat.com>
> >> Cc: Markus Armbruster <armbru@redhat.com>
> >> Cc: Paolo Bonzini <pbonzini@redhat.com>
> >> Reported-by: Jan Tomko <jtomko@redhat.com>
> >> Suggested-by: Markus Armbruster <armbru@redhat.com>
> >> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
> >> Reviewed-by: John Snow <jsnow@redhat.com>
> > 
> > Reviewed-by: Markus Armbruster <armbru@redhat.com>
> 
> Thank you. Can you or John please send a PULL req for this? (Or include
> it in an upcoming PULL of yours.)
> 
> I've been Cc'ing Paolo because the get-maintainer script reported him at
> the top for the patch set, but I believe he might not have time for this
> now.
> 
> Thanks!
> Laszlo

It's listed as part of PC in MAINTAINERS, but looks like
get-maintainer didn't recognize the format.
I fixed it up, will review and queue the patches.
Michael S. Tsirkin June 29, 2015, 9:56 a.m. UTC | #7 
On Mon, Jun 29, 2015 at 11:33:42AM +0200, Markus Armbruster wrote:
> Eduardo Habkost <ehabkost@redhat.com> writes:
> 
> > On Fri, Jun 26, 2015 at 02:50:04PM -0400, John Snow wrote:
> >> On 06/26/2015 08:25 AM, Laszlo Ersek wrote:
> >> > On 06/26/15 11:31, Markus Armbruster wrote:
> >> >> Laszlo Ersek <lersek@redhat.com> writes:
> >> >>
> >> >>> With the pc-q35-2.4 machine type, if the user creates an ISA FDC manually:
> >> >>>
> >> >>>   -device isa-fdc,driveA=drive-fdc0-0-0 \
> >> >>>   -drive file=...,if=none,id=drive-fdc0-0-0,format=raw
> >> >>>
> >> >>> then the board-default FDC will be skipped, and only the explicitly
> >> >>> requested FDC will exist. qtree-wise, this is correct; however such an FDC
> >> >>> is currently not registered in the CMOS, because that code is only reached
> >> >>> for the board-default FDC.
> >> >>>
> >> >>> The pc_cmos_init_late() one-shot reset handler -- one-shot because the
> >> >>> CMOS is not reprogrammed during warm reset -- should search for any ISA
> >> >>> FDC devices, created implicitly (by board code) or explicitly, and set the
> >> >>> CMOS accordingly to the ISA FDC(s) with iobase=0x3f0:
> >> >>>
> >> >>> - if there is no such FDC, report both drives absent,
> >> >>> - if there is exactly one such FDC, report its drives in the CMOS,
> >> >>> - if there are more than one such FDCs, then pick one (it is not specified
> >> >>>   which one), and print a warning about the ambiguity.
> >> >>>
> >> >>> Cc: Jan Tomko <jtomko@redhat.com>
> >> >>> Cc: John Snow <jsnow@redhat.com>
> >> >>> Cc: Markus Armbruster <armbru@redhat.com>
> >> >>> Cc: Paolo Bonzini <pbonzini@redhat.com>
> >> >>> Reported-by: Jan Tomko <jtomko@redhat.com>
> >> >>> Suggested-by: Markus Armbruster <armbru@redhat.com>
> >> >>> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
> >> >>> Reviewed-by: John Snow <jsnow@redhat.com>
> >> >>
> >> >> Reviewed-by: Markus Armbruster <armbru@redhat.com>
> >> > 
> >> > Thank you. Can you or John please send a PULL req for this? (Or include
> >> > it in an upcoming PULL of yours.)
> >> > 
> >> > I've been Cc'ing Paolo because the get-maintainer script reported him at
> >> > the top for the patch set, but I believe he might not have time for this
> >> > now.
> >> > 
> >> > Thanks!
> >> > Laszlo
> >> > 
> >> 
> >> This is technically out-of-tree for me, because it's touching init
> >> instead of my device.
> >> 
> >> Best guess is Eduardo Habkost, whom I have CC'd.
> >
> > Michael is the PC maintainer.
> 
> Michael, we really needs this series in 2.4, because without it floppy
> is broken for Q35.

Will review, thanks for the reminder.
Laszlo Ersek July 6, 2015, 9:58 p.m. UTC | #8 
On 06/29/15 11:56, Michael S. Tsirkin wrote:
> On Mon, Jun 29, 2015 at 11:33:42AM +0200, Markus Armbruster wrote:
>> Eduardo Habkost <ehabkost@redhat.com> writes:
>>
>>> On Fri, Jun 26, 2015 at 02:50:04PM -0400, John Snow wrote:
>>>> On 06/26/2015 08:25 AM, Laszlo Ersek wrote:
>>>>> On 06/26/15 11:31, Markus Armbruster wrote:
>>>>>> Laszlo Ersek <lersek@redhat.com> writes:
>>>>>>
>>>>>>> With the pc-q35-2.4 machine type, if the user creates an ISA FDC manually:
>>>>>>>
>>>>>>>   -device isa-fdc,driveA=drive-fdc0-0-0 \
>>>>>>>   -drive file=...,if=none,id=drive-fdc0-0-0,format=raw
>>>>>>>
>>>>>>> then the board-default FDC will be skipped, and only the explicitly
>>>>>>> requested FDC will exist. qtree-wise, this is correct; however such an FDC
>>>>>>> is currently not registered in the CMOS, because that code is only reached
>>>>>>> for the board-default FDC.
>>>>>>>
>>>>>>> The pc_cmos_init_late() one-shot reset handler -- one-shot because the
>>>>>>> CMOS is not reprogrammed during warm reset -- should search for any ISA
>>>>>>> FDC devices, created implicitly (by board code) or explicitly, and set the
>>>>>>> CMOS accordingly to the ISA FDC(s) with iobase=0x3f0:
>>>>>>>
>>>>>>> - if there is no such FDC, report both drives absent,
>>>>>>> - if there is exactly one such FDC, report its drives in the CMOS,
>>>>>>> - if there are more than one such FDCs, then pick one (it is not specified
>>>>>>>   which one), and print a warning about the ambiguity.
>>>>>>>
>>>>>>> Cc: Jan Tomko <jtomko@redhat.com>
>>>>>>> Cc: John Snow <jsnow@redhat.com>
>>>>>>> Cc: Markus Armbruster <armbru@redhat.com>
>>>>>>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>>>>>>> Reported-by: Jan Tomko <jtomko@redhat.com>
>>>>>>> Suggested-by: Markus Armbruster <armbru@redhat.com>
>>>>>>> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
>>>>>>> Reviewed-by: John Snow <jsnow@redhat.com>
>>>>>>
>>>>>> Reviewed-by: Markus Armbruster <armbru@redhat.com>
>>>>>
>>>>> Thank you. Can you or John please send a PULL req for this? (Or include
>>>>> it in an upcoming PULL of yours.)
>>>>>
>>>>> I've been Cc'ing Paolo because the get-maintainer script reported him at
>>>>> the top for the patch set, but I believe he might not have time for this
>>>>> now.
>>>>>
>>>>> Thanks!
>>>>> Laszlo
>>>>>
>>>>
>>>> This is technically out-of-tree for me, because it's touching init
>>>> instead of my device.
>>>>
>>>> Best guess is Eduardo Habkost, whom I have CC'd.
>>>
>>> Michael is the PC maintainer.
>>
>> Michael, we really needs this series in 2.4, because without it floppy
>> is broken for Q35.
> 
> Will review, thanks for the reminder.

Ping. :)

This should go into 2.4, preferably.

(Tomorrow ^W in two minutes in my timezone is the rc0 / hard freeze date
(according to <http://wiki.qemu.org/Planning/2.4>), but the series is a
bugfix.)

Thanks
Laszlo
diff mbox

Patch

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 4a835be..23616ae 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -335,6 +335,41 @@  typedef struct pc_cmos_init_late_arg {
     BusState *idebus[2];
 } pc_cmos_init_late_arg;
 
+typedef struct check_fdc_state {
+    ISADevice *floppy;
+    bool multiple;
+} CheckFdcState;
+
+static int check_fdc(Object *obj, void *opaque)
+{
+    CheckFdcState *state = opaque;
+    Object *fdc;
+    uint32_t iobase;
+    Error *local_err = NULL;
+
+    fdc = object_dynamic_cast(obj, TYPE_ISA_FDC);
+    if (!fdc) {
+        return 0;
+    }
+
+    iobase = object_property_get_int(obj, "iobase", &local_err);
+    if (local_err || iobase != 0x3f0) {
+        error_free(local_err);
+        return 0;
+    }
+
+    if (state->floppy) {
+        state->multiple = true;
+    } else {
+        state->floppy = ISA_DEVICE(obj);
+    }
+    return 0;
+}
+
+static const char * const fdc_container_path[] = {
+    "/unattached", "/peripheral", "/peripheral-anon"
+};
+
 static void pc_cmos_init_late(void *opaque)
 {
     pc_cmos_init_late_arg *arg = opaque;
@@ -343,6 +378,8 @@  static void pc_cmos_init_late(void *opaque)
     int8_t heads, sectors;
     int val;
     int i, trans;
+    Object *container;
+    CheckFdcState state = { 0 };
 
     val = 0;
     if (ide_get_geometry(arg->idebus[0], 0,
@@ -372,6 +409,23 @@  static void pc_cmos_init_late(void *opaque)
     }
     rtc_set_memory(s, 0x39, val);
 
+    /*
+     * Locate the FDC at IO address 0x3f0, and configure the CMOS registers
+     * accordingly.
+     */
+    for (i = 0; i < ARRAY_SIZE(fdc_container_path); i++) {
+        container = container_get(qdev_get_machine(), fdc_container_path[i]);
+        object_child_foreach(container, check_fdc, &state);
+    }
+
+    if (state.multiple) {
+        error_report("warning: multiple floppy disk controllers with "
+                     "iobase=0x3f0 have been found;\n"
+                     "the one being picked for CMOS setup might not reflect "
+                     "your intent");
+    }
+    pc_cmos_init_floppy(s, state.floppy);
+
     qemu_unregister_reset(pc_cmos_init_late, opaque);
 }
 
@@ -441,9 +495,8 @@  void pc_cmos_init(ram_addr_t ram_size, ram_addr_t above_4g_mem_size,
     val |= 0x02; /* FPU is there */
     val |= 0x04; /* PS/2 mouse installed */
     rtc_set_memory(s, REG_EQUIPMENT_BYTE, val);
-    pc_cmos_init_floppy(s, floppy);
 
-    /* hard drives */
+    /* hard drives and FDC */
     arg.rtc_state = s;
     arg.idebus[0] = idebus0;
     arg.idebus[1] = idebus1;