Re: [edk2-devel] [PATCH v2 15/17] OvmfPkg/PvScsiDxe: Support sending SCSI request and receive response

["Laszlo Ersek" <lersek@redhat.com>]

On 03/28/20 20:18, Liran Alon wrote:

> Sorry for the spam but I think I eventually figured it out.

It's not spam; thank you for the thorough investigation!

> The call-chain in EDK2 looks like this:
> ScsiDiskWriteSectors() (MdeModulePkg/Bus/Scsi/ScsiDiskDxe/ScsiDisk.c)
> ScsiDiskWrite16() (MdeModulePkg/Bus/Scsi/ScsiDiskDxe/ScsiDisk.c)
> ScsiWrite16Command() (MdePkg/Library/UefiScsiLib/UefiScsiLib.c)
> ScsiExecuteSCSICommand() (MdeModulePkg/Bus/Scsi/ScsiBusDxe/ScsiBus.c)
> ExtScsiPassThru->PassThru()
> 
> It can be seen that:
> * ScsiExecuteSCSICommand() just passes Packet to
> ExtScsiPassThru->PassThru() and returns it's return value.
> * ScsiWrite16Command() always updates DataLength with
> Packet->OutTransferLength and returns ScsiExecuteSCSICommand() return
> value.
> * In ScsiDiskWrite16():
>   ** If EFI_BAD_BUFFER_SIZE is returned, NeedRetry is set to TRUE and
> EFI_DEVICE_ERROR is returned.
>   ** Otherwise, if EFI_SUCCESS is returned but HostAdapterStatus is set
> to EFI_EXT_SCSI_STATUS_HOST_ADAPTER_DATA_OVERRUN_UNDERRUN, then again
> NeedRetry is set to TRUE and EFI_DEVICE_ERROR is returned.
>   ** Otherwise, just return EFI_SUCCESS to caller.
> * In ScsiDiskWriteSectors() we finally see the logic we were looking for:
>   ** If ScsiDiskWrite16() returned EFI_SUCCESS, then we break out of
> retry loop and indeed take into account ByteCount. (Which was updated
> from Packet->OutTransferLength).
>   ** Otherwise, (e.g. EFI_BAD_BUFFER_SIZE was returned), if NeedRetry is
> set to TRUE, then next request retry is updated to be done with
> ByteCount (Which was updated from Packet->OutTransferLength).
> 
> So it seems the UEFI-2.8 spec is right and a lot of EDK2 function
> documentation is out-of-date.

On a tangent... Since you mention ScsiDiskWriteSectors(), let me mention commit 5abc2a70da4f ("MdeModulePkg: ScsiDiskDxe: adapt SectorCount when shortening transfers", 2015-09-10), and the related mailing list discussion (this is what I referred to before, when I mentioned that Paolo had looked at the VirtioScsiDxe code twice -- this is the second occasion, from September 2015):

http://mid.mail-archive.com/1441390936-27763-1-git-send-email-lersek@redhat.com

> Therefore, I will update my code accordingly. i.e.:
> 1) Change PvScsi.c PopulateRequest() such that in case TransferLength is
> too big for DMA communication buffer Data field, we update
> TransferLength and return EFI_BAD_BUFFER_SIZE.

Sounds OK.

>     But in addition, for completion, we should also set
> HostAdapterStatus to
> EFI_EXT_SCSI_STATUS_HOST_ADAPTER_DATA_OVERRUN_UNDERRUN and TargetStatus
> to EFI_EXT_SCSI_STATUS_TARGET_GOOD
>     and SenseDataLength to 0 as done in VirtioScsi.c PopulateRequest()
> in case it returns EFI_BAD_BUFFER_SIZE.

OK, thanks.

> 2) Change PvScsi.c HandleResponse() such that:
>   ** If device returned PvScsiBtStatDataUnderrun: Update TransferLength
> with Response->DataLen, set HostAdapterStatus to
> EFI_EXT_SCSI_STATUS_HOST_ADAPTER_DATA_OVERRUN_UNDERRUN and return
> EFI_SUCCESS.

OK.

>   ** If device returned PvScsiBtStatDatarun: Just set HostAdapterStatus
> to EFI_EXT_SCSI_STATUS_HOST_ADAPTER_DATA_OVERRUN_UNDERRUN and return
> EFI_SUCCESS.

Again I'm not familiar with PvScsiBtStatDataUnderrun / PvScsiBtStatDatarun (let alone their differences); I'm OK with this too.

Thanks!
Laszlo