[edk2-devel] ExtScsiPassThru support for Logical SCSI devices

[Laszlo Ersek]

On 07/18/19 18:02, Ravi Kumar Siadri wrote:
> Hi Laszlo Ersek / Hao Wu,
>
> I have gone through the Guide, i can see some points which are not
> very clear..
>
> [...]

Perhaps some examples will help.

In advance, I should mention a few things:

- This is just my interpretation of the spec, and of the guide.

- In my last email, the VenMsg suggestion was wrong. The device paths
  for the physical channel(s) are built by appending Ctrl(n) --
  "controller" -- hardware device path nodes, and not VenMsg() nodes.

- "Logical" means "channel with abstract devices, suitable for data
  access & booting", "Physical" means "channel with physical devices,
  used for diagnostics". A channel may be *both*, if each device on it
  is both physical and logical simultaneously -- that is, it can be used
  for data access / booting, and for low-level diagnostics.

So, the examples:

(A) non-RAID HBA

* Summary:

Handle#1: PciRoot(0x0)/Pci(0x1,0x0)               -- channel where each device is (L + P)
Handle#2: PciRoot(0x0)/Pci(0x1,0x0)/Scsi(0x1,0x0) -- disk that is (L + P)

* Details:

Handle#1:

- device path: PciRoot(0x0)/Pci(0x1,0x0)
- handle created by PciBusDxe [= platform firmware]
- device path protocol installed by PciBusDxe
- PciIo protocol installed by PciBusDxe
- ExtScsiPassThru protocol installed by the SCSI HBA driver, through
  consuming PciIo
- Logical bit set in ExtScsiPassThru: meaning that devices enumerated on
  this channel can be used for data access & booting
- Physical bit set in ExtScsiPassThru: meaning that devices enumerated
  on this channel can be sent diagnostic commands

Handle#2:

- device path: PciRoot(0x0)/Pci(0x1,0x0)/Scsi(0x1,0x0)
- handle created by ScsiBusDxe [= platform firmware]
- device path protocol installed by ScsiBusDxe (here: Target=1, Lun=0)
- ScsiIo protocol installed by ScsiBusDxe [= platform firmware], through
  consuming ExtScsiPassThru on Handle#1
- BlockIo protocol installed by ScsiDiskDxe [= platform firmware],
  through consuming ScsiIo on the same handle (= Handle#2)


(B) RAID HBA

* Summary:

Handle#1: PciRoot(0x0)/Pci(0x1,0x0)                         -- logical channel
Handle#2: PciRoot(0x0)/Pci(0x1,0x0)/Scsi(0x1,0x0)           -- logical disk
Handle#3: PciRoot(0x0)/Pci(0x1,0x0)/Ctrl(0x0)               -- physical channel
Handle#4: PciRoot(0x0)/Pci(0x1,0x0)/Ctrl(0x0)/Scsi(0x4,0x0) -- physical disk #0
Handle#5  PciRoot(0x0)/Pci(0x1,0x0)/Ctrl(0x0)/Scsi(0x4,0x1) -- physical disk #1

* Details:

Handle#1:

- The same as Handle#1 from (A), except the Physical bit is clear in the
  ExtScsiPassThru protocol instance.
- This handle stands for the logical channel.

Handle#2:
- The same as Handle#2 from (A).
- This handle stands for the logical disk.

Handle#3:
- Device path: PciRoot(0x0)/Pci(0x1,0x0)/Ctrl(0x0).
- Handle created by the SCSI HBA driver.
- Device path installed by the SCSI HBA driver.
- ExtScsiPassThru protocol installed by the SCSI HBA driver, through
  consuming PciIo on Handle#1.
- Logical bit is clear in ExtScsiPassThru.
- Physical bit is set in ExtScsiPassThru.
- This handle stands for the physical channel.

Handle#4:
- Device path: PciRoot(0x0)/Pci(0x1,0x0)/Ctrl(0x0)/Scsi(0x4,0x0)
- Handle created by ScsiBusDxe [= platform firmware].
- Device path protocol installed by ScsiBusDxe (here: Target=4, Lun=0).
- ScsiIo protocol installed by ScsiBusDxe [= platform firmware], through
  consuming ExtScsiPassThru on Handle#3.
- BlockIo protocol is *NOT* installed by ScsiDiskDxe [= platform
  firmware], due to the Logical bit being clear in ExtScsiPassThru on
  Handle#3.
- This handle stands for the first physical disk in the array.

Handle#5:
- Same as Handle#4, with the following differences:
- Device path: PciRoot(0x0)/Pci(0x1,0x0)/Ctrl(0x0)/Scsi(0x4,0x1).
- This handle stands for the second physical disk in the array.

Hope this helps,
Laszlo

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