On Tue, Jul 06, 2021 at 04:57:32PM +0100, Andre Przywara wrote:
> On Tue, 6 Jul 2021 19:56:24 +0530
> Jagan Teki <jagan@amarulasolutions.com> wrote:
> 
> Hi Jagan,
> 
> thanks for the response!
> 
> > On Tue, Jul 6, 2021 at 4:53 AM Andre Przywara <andre.przywara@arm.com> wrote:
> > >
> > > The ums command (presenting a U-Boot block device as a USB mass storage
> > > device) is very useful for accessing eMMC devices via USB-OTG.
> > >
> > > At the moment we enable USB fastboot by default for Allwinner devices,
> > > so it makes sense to do the same with USB mass storage, which is
> > > actually more versatile and can be accessed on any USB host easily.
> > >
> > > Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> > > ---
> > >  cmd/Kconfig | 1 +
> > >  1 file changed, 1 insertion(+)
> > >
> > > diff --git a/cmd/Kconfig b/cmd/Kconfig
> > > index a9fb4eead29..7b1c96910a8 100644
> > > --- a/cmd/Kconfig
> > > +++ b/cmd/Kconfig
> > > @@ -1347,6 +1347,7 @@ config CMD_USB_MASS_STORAGE
> > >         bool "UMS usb mass storage"
> > >         select USB_FUNCTION_MASS_STORAGE
> > >         depends on BLK && USB_GADGET
> > > +       default y if ARCH_SUNXI && USB_MUSB_GADGET
> > 
> > UMS or any secondary-emmc accessible are considered in production
> > u-boot config instead of mainline u-boot since we have fastboot
> > already available for this kind of purpose. This might be one of the
> > reason not conisidered UMS by default till now, atleast on Allwinner.
> 
> Well, I consider fastboot inferior to UMS. I understand that
> Android phone hackers use it all the time, but I think having a block
> device is far more versatile - you can partition it as you like, create
> and populate a filesystem, dd an image to it, extract or update
> firmware, etc. - most without extra software, even on Windows or Mac.
> I think fastboot offers a reboot command, but are there other killer
> reasons for it? And having the ums command in addition to fastboot does
> not hurt, both would still work.

fastboot abstracts away the storage medium, whereas UMS doesn't. You
cannot run UMS on a NAND or SPI-NOR, while this causes no issue at all
to fastboot.

Similarly, UMS exposes the whole partition to the host. You then need to
have a driver for that FS on that machine, otherwise you just can't
access it.

Sure, it's convenient, but it's far from being ubiquitous and the silver
bullet you claim it is.

> So are there any real arguments for not adding ums as well? I am not
> sure many people tweak their config, so I would like to offer a decent
> out-of-the-box experience, even for casual users.

As usual, we also have to balance that with the size limit, but I'm not
sure it's an issue these days?

Maxime