[PATCH v2 0/3] Support usb booting on i.MX8MP

["Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>]

Hello,

compared to (implicit) v1, the following changed here:

 - be a bit more conservative in "imx-usb-loader: Add support for
   i.MX8MP" regarding last_transfer; feedback by Sascha Hauer

 - Add support in PBL to be actually booted using imx-usb-loader (only
   tested the vendor U-Boot for v1), also skip the barebox header (i.e.
   the first (usually) 0x8000 bytes) before the IVT header on uploadeing

There are two things that resulted in discussions between Lucas, Ahmad
and me during development of this series:

 - On i.MX8MM and i.MX8MQ after the PBL is uploaded it's followed up by
   the complete image. So the PBL is uploaded twice. The motivation for
   this behaviour was that when booting from MMC loading from offset 0
   is easier because depending on the mode the hardware is in the offset
   has to be specified in different ways. So to make the two modes more
   similar the PBL is loaded twice for both modes.

   Here however after the PBL only the piggy data is sent because it
   feels wrong for me to spend some extra effort in imx-usb-loader to do
   a kludge for USB just because there are some difficulties with MMC.

   Arguments for this choice (apart from that already being completed
   and tested :-) are:

   - No duplication of data that is overwritten anyhow
   - Better interoperability with U-Boot/mfg-tools
     While this is usually not our focus I consider it quite annoying
     that there are at least three implementations of imx-usb-loader and
     depending on which machine and bootloader you use you have to pick
     the right implementation. With the longterm goal to have
     imx-usb-loader and barebox available in Debian some
     interoperability would be nice.

   I quickly tried using the boot rom load image support when booting
   from SD, but it didn't work out of the box and I didn't debug that.
   However I imagine that in this mode it would also be more natural to
   not expect the PBL twice.

   Switching to the duplicated operation mode would make imx-usb-loader
   a bit more complicated (because in the MXS code path the duplication
   isn't available yet), in return we'd save an offset calculation in
   the PBL.

   I should be possible to look at the first post-PBL data chunk coming
   in via USB and judge which mode of operation is used and behave
   accordingly. If this is considered a good idea I can create a patch
   for that.

 - When booting via USB the boot source is identified as "serial". I
   would expect that the semantic of that is rs232 and not USB. The
   source of this confusion is probably that the Reference Manual calls
   the USB  boot mode "USB Serial Download boot". I stuck to
   BOOTSOURCE_SERIAL here for consistency. If it's not only me who would
   consider using BOOTSOURCE_USB instead a fix this should be changed
   consistently for all i.MX platforms.
   Ahmad pointed out that this might break barebox shell scripts.

Uwe Kleine-König (3):
  imx8mp-evk: Add support for booting via USB
  imx-usb-loader: Drop nearly unused struct usb_id
  imx-usb-loader: Add support for i.MX8MP

 arch/arm/boards/nxp-imx8mp-evk/lowlevel.c |  27 +++++
 arch/arm/mach-imx/boot.c                  |   4 +-
 include/asm-generic/sections.h            |   1 +
 scripts/imx/imx-usb-loader.c              | 131 ++++++++++++----------
 4 files changed, 103 insertions(+), 60 deletions(-)


base-commit: 72424fd057d135ec0e41139fe4cb5740471d33a5
-- 
2.30.2


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