Re: [PULL 4/5] hw/ufs: Support for UFS logical unit

[Jeuk Kim <jeuk20.kim@gmail.com>]

On 23. 9. 15. 02:31, Paolo Bonzini wrote:
> On 9/7/23 20:16, Stefan Hajnoczi wrote:
>> From: Jeuk Kim<jeuk20.kim@samsung.com>
>>
>> This commit adds support for ufs logical unit.
>> The LU handles processing for the SCSI command,
>> unit descriptor query request.
>>
>> This commit enables the UFS device to process
>> IO requests.
>>
>> Signed-off-by: Jeuk Kim<jeuk20.kim@samsung.com>
>> Reviewed-by: Stefan Hajnoczi<stefanha@redhat.com>
>> Message-id:beacc504376ab6a14b1a3830bb3c69382cf6aebc.1693980783.git.jeuk20.kim@gmail.com 
>>
>> Signed-off-by: Stefan Hajnoczi<stefanha@redhat.com>
>> ---
>
> Jeuk,
>
> can you explain the differences between scsi-hd and ufs-lu, apart from 
> the different bus type?  Ideally, the UFS controller would be in 
> hw/scsi/ufs.c and there would be no need for ufs-lu at all.
>
> Would it make sense to allow any SCSI device into a UFS bus without 
> the need to have duplicate code?
>
> Thanks!
>
> Paolo
>
>

Hi Paolo,


While ufs does use the SCSI specification to communicate with the driver,

it doesn't behave exactly like a typical scsi device.


First, ufs-lu has a feature called "unit descriptor". This feature shows 
the status of the ufs-lu

and only works with UFS-specific "query request" commands, not SCSI 
commands.


UFS also has something called a well-known lu. Unlike typical SCSI 
devices, where each lu is independent,

UFS can control other lu's through the well-known lu.


Finally, UFS-LU will have features that SCSI-HD does not have, such as 
the zone block command.


In addition to this, I wanted some scsi commands to behave differently 
from scsi-hd, for example,

the Inquiry command should read "QEMU UFS" instead of "QEMU HARDDISK",

and the mode_sense_page command should have a different result.


For these reasons, I chose to generate the ufs-lu code separately.


Please let me know if you have any comments on this.


Thanks!

Jeuk