It was previously in beta (may still be). I've been using this feature for some time now (at least 2-3 months I feel?).

The bootloader with USB support was first marked "stable" on 2020-06-17. This post is about a firmware with USB boot support being released on the "critical" update channel, which Raspbian will install by default without any user intervention.

I know it was in beta. Maybe it's now the default?

"USB msd boot support is now available in the default bootloader version 2020-09-03"

(although the page you reference doesn't really reflect that - see the last paragraph)

I can confirm that it is the default now. I installed a PI4 yesterday (ordered it right after release). I installed Raspberry Pi OS on an sd card first. When I tried to update eeprom, it was already up to date. After flashing the RPI OS image on an ssd, it worked perfectly fine. I did not have to touch a command line to make it boot from ssd.

I see in the docs for "Pi 4 Bootloader Configuration", under the BOOT_ORDER setting:

- 0x4 - USB mass storage boot (since 2020-09-03)

https://www.raspberrypi.org/documentation/hardware/raspberry...

I've been doing this on a 3B for almost a year now. (At least I think it's a 3B; it's not a 4 in any case. The article title has since been updated to clarify that the change is relevant to the 4.)

IIRC, enabling usb mass storage boot involves setting some OTP bits, which permanently disables usb host boot. But AFAIK, the 3B doesn't support usb host boot anyways. Is there any feature you could lose by enabling mass storage boot in this case?

I think (but haven't checked) that you lose the ability to boot from a microSD. I just switched it to USB because I wanted higher reliability for a semi-permanent installation and never checked if it would boot from SD if I removed the USB.

It will still boot from SD. Enabling USB boot just adds USB booting at the end of the list of things checked to boot from.

Thanks. I wonder what's with the dire warning about changing the OTP bits then? https://www.raspberrypi.org/documentation/hardware/raspberry...

The dire warning is mostly for the 3A+, where enabling USB host boot mode (which allows booting from USB mass storage devices) will permanently prevent booting in USB device mode. (Maybe...see below).

Device mode is only supported on the Compute Module, CM3, Zero, Zero W, A, A+, and 3A+, so if you don't have one of those there is nothing to worry about as far as this goes.

It still deserves a warning on other models, but not a dire warning. It's still permanent, but it is much harder for that to be a problem. It will only be a problem if you are going to have situations where you will have a bootable USB drive attached at boot time, without a bootable SD card inserted, and you will want it to not boot rather than boot from the USB drive.

Although OTP changes are permanent, it looks like there is still a way to sort of work around the USB host boot mode one, albeit at a cost of losing access to 7 GPIOs or at least making them a lot harder to use. With another irreversible OTP change, you can tell your Pi to determine what devices to consider booting from by looking at 7 GPIOs [1]. Using GPIO boot mode, you could easily switch between SD card only, USB only, and SD followed by USB, and device mode, by just changing pull up resistors on the relevant GPIOs.

[1] https://www.raspberrypi.org/documentation/hardware/raspberry...

Burning the OTP will prevent you from starting the 3A or 4 in OTG mode; you can still do that in software by dynamically loading the dwc2 overlay once Linux has booted up and specifying the mode=peripheral parameter (then loading the kernel module).

The 4 is a bit different under the hood (as evidenced by the different procedures). There was support on the older models, while the 4 launched without it.

I believe this applies to the RPi4 only.