Re: [Qemu-devel] [PATCH 04/25] ahci: add ide device initialization helper

[Jason Baron]

On Wed, Sep 26, 2012 at 10:15:39AM +0200, Markus Armbruster wrote:
> Jason Baron <address@hidden> writes:
> 
> > On Mon, Sep 24, 2012 at 06:52:29PM +0200, Markus Armbruster wrote:
> >> Jason Baron <address@hidden> writes:
> >> 
> >> > On Fri, Sep 21, 2012 at 04:05:14PM +0200, Markus Armbruster wrote:
> >> >> Jason Baron <address@hidden> writes:
> >> >> 
> >> >> > From: Isaku Yamahata <address@hidden>
> >> >> >
> >> >> > Introduce a helper function which initializes the ahci port with
> >> >> > ide devices.
> >> >> > It will be used by q35 support.
> >> >> >
> >> >> > Cc: Alexander Graf <address@hidden>
> >> >> > Signed-off-by: Isaku Yamahata <address@hidden>
> >> >> > Signed-off-by: Jason Baron <address@hidden>
> >> >> > ---
> >> >> >  hw/ide.h      |    3 +++
> >> >> >  hw/ide/ahci.c |   16 ++++++++++++++++
> >> >> >  2 files changed, 19 insertions(+), 0 deletions(-)
> >> >> >
> >> >> > diff --git a/hw/ide.h b/hw/ide.h
> >> >> > index 2db4079..8df872e 100644
> >> >> > --- a/hw/ide.h
> >> >> > +++ b/hw/ide.h
> >> >> > @@ -36,4 +36,7 @@ int ide_get_bios_chs_trans(BusState *bus, int unit);
> >> >> >  /* ide/core.c */
> >> >> >  void ide_drive_get(DriveInfo **hd, int max_bus);
> >> >> >  
> >> >> > +/* ide/ahci.c */
> >> >> > +void pci_ahci_ide_create_devs(PCIDevice *pci_dev, DriveInfo 
> >> >> > **hd_table);
> >> >> > +
> >> >> >  #endif /* HW_IDE_H */
> >> >> > diff --git a/hw/ide/ahci.c b/hw/ide/ahci.c
> >> >> > index 5ea3cad..9561210 100644
> >> >> > --- a/hw/ide/ahci.c
> >> >> > +++ b/hw/ide/ahci.c
> >> >> > @@ -1260,3 +1260,19 @@ static void sysbus_ahci_register_types(void)
> >> >> >  }
> >> >> >  
> >> >> >  type_init(sysbus_ahci_register_types)
> >> >> > +
> >> >> > +void pci_ahci_ide_create_devs(PCIDevice *pci_dev, DriveInfo 
> >> >> > **hd_table)
> >> >> > +{
> >> >> > + struct AHCIPCIState *dev = DO_UPCAST(struct AHCIPCIState, card,
> >> >> > pci_dev);
> >> >> > +    int i;
> >> >> > +
> >> >> > +    for (i = 0; i < dev->ahci.ports; i++) {
> >> >> > +        /* master device only, ignore slaves */
> >> >> > +        if (hd_table[i * MAX_IDE_DEVS] == NULL) {
> >> >> > +            continue;
> >> >> > +        }
> >> >> > +        ide_create_drive(&dev->ahci.dev[i].port, 0,
> >> >> > +                         hd_table[i * MAX_IDE_DEVS]);
> >> >> > +    }
> >> >> > +}
> >> >> > +
> >> >> 
> >> >> Ignores odd entries in hd_table[] (MAX_IDE_DEVS is 2).  Here's my
> >> >> attempt at explaining why.
> >> >> 
> >> >> -drive has parameters bus, unit, and index.  index and (bus, unit) are
> >> >> related in a well-known way that depends on parameter if.  For if=ide,
> >> >> index = bus * 2 + unit.  This relationship is ABI, i.e. it cannot be
> >> >> changed.
> >> >> 
> >> >> "bus * 2 + unit" makes sense for IDE, because each IDE bus can connect
> >> >> two IDE devices, "master" and "slave".
> >> >> 
> >> >> Boards implementing IDE reject drives with (bus, unit) that make no
> >> >> sense for the board's IDE controller(s).  A typical board has a single
> >> >> controller with two buses, which means bus > 1 get rejected.
> >> >> 
> >> >> q35 implements AHCI instead of IDE.  It connects if=ide drives to AHCI,
> >> >> because that's felt to be convenient.
> >> >> 
> >> >> An AHCI port can connect a single AHCI device, unlike an IDE bus.  This
> >> >> patch identifies maps -drive's bus to AHCI port number.
> >> >> 
> >> >> PATCH 11/25 sets up argument hd_table[] as follows:
> >> >> 
> >> >>     ide_drive_get(hd, MAX_SATA_PORTS);
> >> >> 
> >> >> This rejects bus > MAX_SATA_PORTS.  It doesn't reject unit == 1.  I
> >> >> believe these get silently ignored.  Bug or feature?
> >> >> 
> >> >> Should we reject unit == 1 instead?
> >> >> 
> >> >> Should we map -drive's index to AHCI port number instead?
> >> >
> >> > Right, so now that we have ide disks that can be attached to either the
> >> > legacy ide controller or to ahci, I think we need to differentiate which
> >> > controller we mean. That is, as proposed q35 is treating -drive if=ide
> >> > as an ide attached to the ahci controller. I think that is broken
> >> > behavior b/c we need a way to differentiate between the controllers.
> >> 
> >> What exactly is broken?
> >> 
> >
> > I think that -drive if=ide should result in a disk attached piix3-ide.
> > Not in an ide disk attached to the ahci controller (which is current q35
> > bahavior, and is 'broken' b/c we don't want that to change after q35 is
> > introdued). The reason being is that I think there should be an easy way
> > to create an ide drive on piix3-ide, and an ide drive on the ahci
> > controller. But it sounds like you don't agree with this point.
> 
> Two issues with that:
> 
> 1. Why should q35 have a piix3-ide?  The ICH9 southbridge provides only
> SATA, so the board needs additional circuitry to provide PATA.  As far
> as I can tell, intel's Q35 doesn't.  ICH9-based boards that do certainly
> won't use a piix3-ide, because that's a *function* of the PIIX
> southbridge device.  It doesn't exist separately.
> 
> 2. Why should we connect -drive if=ide to a slow PATA controller instead
> of a perfectly servicable SATA controller?
> 

The only way I can install windows xp, and various bsd flavors at the
momemnt is by using the PATA controller.

> >> > As Alexander Graf has proposed before, I think we need a -drive if=ahci
> >> > introduced. In that case, I think we reject unit > 0, as you've
> >> > suggested.
> >> 
> >> Achieved by setting if_max_devs[IF_AHCI] to one.  bus becomes an alias
> >> for index, and unit must be zero.
> >> 
> >> Alternatively, keep if_max_devs[IF_AHCI] zero.  Swaps role of bus and
> >> unit.
> >> 
> >> Alex had if_max_devs[IF_AHCI] = 6.
> >> 
> >> > In terms of the current q35 patch series, I think the first step would
> >> > be to introduce the ahci interface type, and have hda-hdd be added with
> >> > the default type for q35 of ahci. Then, we can simply fetch ahci drives
> >> > of index 0-3, and populate the controller, without any of this skipping
> >> > odd numbers stuff.
> >> >
> >> > The next step would then to add if=ahci interface to -drive.
> >> 
> >> We discussed if=ahci at length before, without reaching consensus.  I'd
> >> rather not rehash the old arguments again.  Instead, let's examine how
> >> the command line should behave, and only then figure out how to get
> >> that.
> >> 
> >> 1. Drives created with -hd[a-d], -cdrom, or the non-option image
> >>    argument should connect to well-known connectors of the board's
> >>    preferred controller.
> >> 
> >>    For current pc, the preferred controller is piix3-ide.  -hda connects
> >>    to its primary bus as master, -hdb as slave.  -hdc connects to its
> >>    secondary bus as master, -hdd as slave.
> >> 
> >>    For pseries, the preferred controller is spapr-vscsi.  -hda connects
> >>    as SCSI ID 0, -hdb as 1, and so forth.
> >> 
> >>    For s390-virtio, the preferred controller is virtio-blk-s390.  -hda
> >>    and -hdb connect to their own virtio-blk-s390 controller, -hdc and
> >>    -hdd get silently ignored.  Yes, that's wacky.  Your current q35
> >>    patch is similarly wacky, as far as I can tell: -hdb and -hdd get
> >>    silently ignored.
> >> 
> >>    For q35, the preferred controller is ich9-ahci.  I'd expect -hda to
> >>    connect to port 0, -hdb to port 1, and so forth.
> >> 
> >>    Below the hood, -hda is currently like -drive index=0,media=disk,
> >>    -hd[b-d] same with index=1..3, and -cdrom is like -drive
> >>    index=2,media=cdrom, independent of the board.
> >> 
> >>    It follows that -cdrom connects to the same connector as -hdc for all
> >>    boards.  Fine for pc, but may not be as fine for some other boards.
> >>    You can't use both -hdc and -cdrom at the same time.
> >> 
> >>    The non-option image argument is equivalent to -hda.  You can't use
> >>    both at the same time.
> >> 
> >> 2. Drives created with -drive without if, index, bus, and unit connect
> >>    to the next unused connector of the board's preferred controller.
> >> 
> >>    If all connectors are in use, behavior currently depends on the
> >>    board, I think.
> >> 
> >> 3. -drive parameters (if, index) provide more control over the connector
> >>    to use.
> >> 
> >>    Which controller you get for which if depends on the board.  So does
> >>    the meaning of index.  The details can get messy.
> >> 
> >>    For instance, drives with (if, index) the board doesn't support
> >>    sometimes get ignored silently, and sometimes get flagged as error.
> >> 
> >>    Currently, -drive without parameter if is equivalent to either if=ide
> >>    or if=scsi.  Could be changed for new machine types.
> >> 
> >>    For q35, -drive index=0..5 should connect to ports 0..5 of the
> >>    board's ich9-ahci.   
> >> 
> >> 4. -drive parameters (bus, unit) are an alternate way to specify
> >>    parameter index.  The mapping between index and (bus, unit) depends
> >>    on the board.
> >> 
> >>    Actually, it depends only on parameter if right now.  For if=ide,
> >>    index = bus * 2 + unit, unit<2.  For if=scsi, index = bus * 7 + unit,
> >>    unit < 7.  For everything else, index = unit, bus = 0.  We might want
> >>    to make it depend on the board, see commit 27d6bf40.
> >> 
> >>    For q35, we want index = bus * 6 + unit, unit<5.
> >> 
> >>    An easy way to get that is new if=ahci.  Backfires when an AHCI
> >>    controller with a different number of ports shows up.
> >> 
> >
> > I agree with points 1-4.
> >
> >>    We really should make the mapping between index and (bus, unit)
> >>    depend on the board.  And then we can just as well use if=ide to
> >>    refer to q35's one and only IDE-like controller ich9-ahci.
> >
> > I agree mapping should depend on the board.
> 
> We agree on the important things then.
> 
> > But I'm not sure about using if=ide to use ich9-ahci. I'm suggesting
> > that if=ide should continue to refer to piix3-ide.
> 
> Perhaps it should mean "the board's preferred ATA controller", perhaps
> it should mean "the board's preferred PATA controller".  Certainly
> debatable.
> 
> If the latter, not necessarily piix3-ide.
> 

Sure. My main point was that 'if=ide' in the q35 context doesn't specify a SATA
controller. I think it would be nice to have a short hand way of specify both
PATA and SATA on q35.

Thanks,

-Jason