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From: Gerd Hoffmann <kraxel@redhat.com>
Date: Wed, 14 Dec 2016 10:36:05 +0100
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Subject: Re: [Qemu-devel] [PATCH] hw/ppc/spapr: Fix boot path of usb-host
 storage devices
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To: Thomas Huth <thuth@redhat.com>
Cc: David Gibson <david@gibson.dropbear.id.au>, qemu-devel@nongnu.org, Alexander Graf <agraf@suse.de>, qemu-ppc@nongnu.org

  Hi,

> >> in the /chosen/qemu,boot-list property. SLOF, however, probes the
> >> USB device, recognizes that it is a storage device and thus changes
> >> its name to "storage", and additionally adds a child node for the
> >> SCSI LUN, so the correct boot path in SLOF is something like
> >> "/pci@800000020000000/usb@0/storage@1/disk@101000000000000" instead.

Sure this is correct?

usb-storage (aka virtual usb stick) creates paths like this:

  /pci@i0cf8/usb@1,2/storage@1/channel@0/disk@0,0

i.e. there is a extra channel element (probably for host adapters with
multiple scsi busses).

> >> So when we detect an USB mass storage device with SCSI interface,
> >> we've got to adjust the firmware boot-device path properly, so that
> >> SLOF can automatically boot from the device.

> > Any reason why this is hidden in ppc/spapr?
> >=20
> > usb-host could implement the ->fw_name callback instead to create a nam=
e
> > depending on the device type ...

> The naming is specific to SLOF ... not sure what happens with other
> firmware implementations, so spapr.c sounds like the better place to me
> right now.

If usb-host (and usb-redir too btw) create paths identical to the ones
created by usb-storage.  Existing firmware should cope just fine
(assuming bootindex for usb-storage works).

cheers,
  Gerd