[edk2-devel] ExtScsiPassThru support for Logical SCSI devices

[Wu, Hao A]

Hello Ravi Kumar,

Inline comments below:

From: devel at edk2.groups.io [mailto:devel at edk2.groups.io] On Behalf Of Ravi Kumar Siadri
Sent: Wednesday, June 12, 2019 12:01 PM
To: devel at edk2.groups.io
Subject: Re: [edk2-devel] ExtScsiPassThru support for Logical SCSI devices

Hi,

Can someone help me in clarifying my queries ??

Thanks,
Ravi Kumar

On Mon, Jun 10, 2019 at 3:55 PM Ravi Kumar Siadri <siadriravikumaruefi at gmail.com<mailto:siadriravikumaruefi at gmail.com>> wrote:
Hi all,

I have couple of queries regarding the EFI_EXT_SCSI_PASS_THRU_ATTRIBUTES_LOGICAL attribute support in EFI_EXT_SCSI_PASS_THRU_PROTOCOL.

1.
The Attributes field of the EFI_EXT_SCSI_PASS_THRU_PROTOCOL interface tells if the interface is for physical SCSI devices or logical SCSI devices. Drivers for non-RAID SCSI controllers will set both the EFI_EXT_SCSI_PASS_THRU_ATTRIBUTES_PHYSICAL, and the EFI_EXT_SCSI_PASS_THRU_ATTRIBUTES_LOGICAL bits.

If the Drivers is for non-RAID SCSI controllers why to set the EFI_EXT_SCSI_PASS_THRU_ATTRIBUTES_LOGICAL bit. Will there be any case that non-RAID SCSI controllers have Logical devices connected to it ??

Per my understanding, every partition on a physical HW device will be treated
as a logical device by the firmware.

So for non-RAID case, both bits will be set for the PassThru protocol produced
for the physical device.


2.
Drivers for RAID controllers that allow access to the physical devices and logical devices will produce two EFI_EXT_SCSI_PASS_THRU_PROTOCOL interfaces:
One with the just the EFI_EXT_SCSI_PASS_THRU_ATTRIBUTES_PHYSICAL bit set and another with just the EFI_EXT_SCSI_PASS_THRU_ATTRIBUTES_LOGICAL bit set. One interface can be used to access the physical devices attached to the RAID controller, and the other can be used to access the logical devices attached to the RAID controller for its current configuration.

Any background why EFI_EXT_SCSI_PASS_THRU_PROTOCOL needed 2 instances ? why can't we install attributes EFI_EXT_SCSI_PASS_THRU_ATTRIBUTES_LOGICAL and EFI_EXT_SCSI_PASS_THRU_ATTRIBUTES_PHYSICAL on same Instance ??
How User locates the Instance with EFI_EXT_SCSI_PASS_THRU_ATTRIBUTES_LOGICAL bit set and Instance with EFI_EXT_SCSI_PASS_THRU_ATTRIBUTES_PHYSICAL bit set. ??

UEFI spec allows RAID drivers to only produce one PassThru protocol interface
with just the XXX_PASS_THRU_LOGICAL bit set when the RAID controller select to
not allow direct access to the underlying physical devices.


Thanks,
Ravi Kumar



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