Re: Universal Flash Storage Driver Proposal

On Thu, Mar 13, 2025 at 11:28 PM Jaeyoon Choi <j_yoon.choi@samsung.com>
wrote:

> Hi Warner,
> I'm back in the office :).
>
> > I've been studying UMASS and have a different idea. I'm starting to not
> > like the PIM flags
> > now that I've read it.
> >
> > There's about a dozen commands that different USB flash devices can't do
> in
> > various ways.
> > I've started to convert umass to just fail the command as illegal when a
> > bad command is
> > sent to it. I've also been modifying the da, cd, etc drivers to notice
> the
> > illegal commands and
> > modify its behavior. It isn't a new idea: the periph drivers have been
> > doing it to cope with
> > drives that don't support READ(6) commands. It's recently (in the last 5
> > years) expanded to
> > dealing with other commands like SYNCHRONIZE CACHE, MODE SENSE.
> >
> > The idea is to allow the device to reject the command as illegal. In the
> > cases of reduced SCSI
> > command sets, like RBC, UFS, etc the SIM should reject known bad commands
> > at the SIM
> > layer because history has shown that some of the
> > lower-quality-but-still-working-enough drives
> > can hang when unexpected commands are sent to them.
> >
> > Not supporting MODE SENSE(6) likely is going to be a somewhat larger
> change.
>
> I will follow up on your UMASS modification.
> And if you give me a guide, I'll follow it
>

Yes. Changing MODE SENSE(6) to MODE SENSE(10) likely will cause problems
with some completion routines, but that's fixable.

I'm about to commit a number of changes that will show how to 'reject'
commands
properly.


> > Test how? I'm not sure I understand this question well enough to answer,
> > so maybe a few examples will help me focus an answer.
>
> I was wondering how you do unit tests and integration tests for device
> drivers.
> Is there a framework to write unit tests when developing a device driver?
> Is there any tool you use for Integration test (e.g. FIO(flexible I/O
> tester))
> (I'm a FreeBSD newbie, so please forgive me if this is a stupid question).
>

FIO would work. It will do the basic I/O. But it destroys the data on the
drive.
For testing purposes, though, it's fine.


> > In the mean time, I'll see if I can locate a copy of the UFS standard
> > or a reasonable summary. The ones at jedec.org are a bit too expensive
> > for me to buy on my own. I've found excerpts of it datasheets at best,
> which
> > may suffice for my review needs.
>
> If you register with JEDEC, you can get the documentation for UFS 2.1
> version
> for free, although it is not the latest spec.
> There are two documents to look at for the UFS specification.
> UFSHCI, which is the host interface, and UFS, which is the device.
> - UFS 2.1 spec: https://www.jedec.org/system/files/docs/JESD220C-2_1.pdf
> - UFSHCI 2.1 spec:
> https://www.jedec.org/sites/default/files/docs/JESD223C.pdf


I've grabbed these. Thanks. I also found some vague command lists for newer
versions in data sheets.

My implementation will be based on UFS 4.1, but the basics are the same.
> The main differences between UFS 2.1 and 4.1 are as follows
> - I/O queue changed from single queue to multi-queue
> - Maximum HS-GEAR changed from 3 -> 5, which improves bandwidth
> - Supports Write Booster (SLC caching)
> - Supports Host Performance Booster (HPB)
>
> I will explain the specification changes when I request a review of the
> features added in UFS 4.1.
>

Great! That would be perfect. The last two look interesting...

Warner


> Thanks,
> Jaeyoon
>