[U-Boot] [PATCH v5 05/18] arm: MediaTek: add basic support for MT7623 boards

Tue Nov 27 01:02:26 UTC 2018

Hi Weijie,

On Mon, 19 Nov 2018 at 23:36, Weijie Gao <weijie.gao at mediatek.com> wrote:
>
> Hi Simon,
>
> On Mon, 2018-11-19 at 10:14 -0700, Simon Glass wrote:
> > Hi Weijie,
> >
> > On Mon, 19 Nov 2018 at 00:16, Weijie Gao <weijie.gao at mediatek.com> wrote:
> > >
> > > On Fri, 2018-11-16 at 11:26 -0700, Simon Glass wrote:
> > > > Hi Weijie,
> > > >
> > > > On 15 November 2018 at 23:08, Weijie Gao <weijie.gao at mediatek.com>
> > > > wrote:
> > > > > On Thu, 2018-11-15 at 11:21 -0800, Simon Glass wrote:
> > > > >> Hi,
> > > > >>
> > > > >> On 14 November 2018 at 18:07, Ryder Lee <ryder.lee at mediatek.com>
> > > > wrote:
> > > > >> > From: Weijie Gao <weijie.gao at mediatek.com>
> > > > >> >
> > > > >> > This adds a general board file based on MT7623 SoCs from
> > > > MediaTek.
> > > > >> >
> > > > >> > As this u-boot is loaded by MTK proprietary preloader, there is
> > > > no
> > > > >> > low level initializtion codes.
> > > > >> >
> > > > >> > Signed-off-by: Weijie Gao <weijie.gao at mediatek.com>
> > > > >> > Signed-off-by: Ryder Lee <ryder.lee at mediatek.com>
> > > > >> > Tested-by: Matthias Brugger <matthias.bgg at gmail.com>
> > > > >> > ---
> > > > >> > Changes since v5: None
> > > > >> > Changes since v4:
> > > > >> > -Add gd->bd->bi_boot_params for legacy method - ATAGs.
> > > > >> > ---
> > > > >> >  arch/arm/mach-mediatek/Kconfig                | 13 ++++
> > > > >> >  arch/arm/mach-mediatek/Makefile               |  1 +
> > > > >> >  arch/arm/mach-mediatek/mt7623/Makefile        |  4 ++
> > > > >> >  arch/arm/mach-mediatek/mt7623/init.c          | 54
> > > > +++++++++++++++
> > > > >> >  arch/arm/mach-mediatek/mt7623/lowlevel_init.S | 22 ++++++
> > > > >> >  arch/arm/mach-mediatek/mt7623/preloader.h     | 99
> > > > +++++++++++++++++++++++++++
> > > > >> >  board/mediatek/mt7623/Kconfig                 | 13 ++++
> > > > >> >  board/mediatek/mt7623/MAINTAINERS             |  7 ++
> > > > >> >  board/mediatek/mt7623/Makefile                |  3 +
> > > > >> >  board/mediatek/mt7623/mt7623_rfb.c            | 16 +++++
> > > > >> >  configs/mt7623n_bpir2_defconfig               | 54
> > > > +++++++++++++++
> > > > >> >  include/configs/mt7623.h                      | 56
> > > > +++++++++++++++
> > > > >> >  12 files changed, 342 insertions(+)
> > > > >> >  create mode 100644 arch/arm/mach-mediatek/mt7623/Makefile
> > > > >> >  create mode 100644 arch/arm/mach-mediatek/mt7623/init.c
> > > > >> >  create mode 100644 arch/arm/mach-mediatek/mt7623/lowlevel_init.S
> > > > >> >  create mode 100644 arch/arm/mach-mediatek/mt7623/preloader.h
> > > > >> >  create mode 100644 board/mediatek/mt7623/Kconfig
> > > > >> >  create mode 100644 board/mediatek/mt7623/MAINTAINERS
> > > > >> >  create mode 100644 board/mediatek/mt7623/Makefile
> > > > >> >  create mode 100644 board/mediatek/mt7623/mt7623_rfb.c
> > > > >> >  create mode 100644 configs/mt7623n_bpir2_defconfig
> > > > >> >  create mode 100644 include/configs/mt7623.h
> > > > >>
> > > > >> Can this use the bloblist feature which should land soon?
> > > > >>
> > > > >> For now, see dm/spl-working.
> > > > >>
> > > > >> Regards,
> > > > >> Simon
> > > > >
> > > > > Hi Simon,
> > > > >
> > > > > I've read the code for spl handoff. It's a good way though but
> > > > > unfortunately it cannot be applied to the MT7623 boards.
> > > > >
> > > > > The reason is that MT7623 uses a MediaTek proprietary preloader
> > > > which
> > > > > has the same function as the U-Boot SPL. But the preloader is
> > > > > close-sourced (by company policy) and only available in binary
> > > > release.
> > > > > This means we can't use a real U-Boot SPL to replace the preloader.
> > > >
> > > > Can you work to get U-Boot SPL running on the chip?
> > > >
> > > > What is the reason for the proprietary SPL?
> > > >
> > > > >
> > > > > At present this chip has already been used in many products. We
> > > > can't
> > > > > either release a different preloader which introduces compatibility
> > > > > issues.
> > > >
> > > > What sort of compatibility issues? I cannot see any advantage with a
> > > > proprietary SPL.
> > > >
> > > > >
> > > > > So the conclusion is that we cannot use the bloblist feature for
> > > > this
> > > > > SoC.
> > > >
> > > > Regards,
> > > > Simon
> > > >
> > > Hi Simon,
> > >
> > >
> > > Sorry for that I didn't describe the function of the preloader clearly.
> > >
> > > The MT7623 is like a smart phone SoC which has the ability to upgrade
> > > bootloader/firmware via a USB cable. This function is always available
> > > even if there is no valid preloader/bootloader.
> > >
> > > This is done by cooperation of the BootROM and preloader. This is a
> > > simple description of the flow:
> > > 1. Connect the MT7623 board to the PC using USB cable. Do not power up.
> > > 2. Run MediaTek's FlashTool and start downloading.
> > > 3. Power up the board.
> > > 4. The BootROM will initialize the USB device immediately for few
> > >    seconds and waiting for commands from PC.
> > > 5. The PC will start transmit commands to the board as soon as it
> > >    detects the board device.
> > > 6. Thee BootROM will then download the preloader into SRAM, and run it.
> > >    Several informations will be passed to the preloader, to let it
> > >    continue to communicate with the FlashTool.
> > > 7. The preloader will initialize the DRAM, download data via USB and
> > >    write it to flash.
> > >
> > > So the preloader is not only a simple SPL. It initializes DRAM and many
> > > other components which will only be initialized once or used by
> > > preloader. It also performs USB downloading and other things.
> > >
> > > The preloader is also used by other MediaTek's smart phone SoCs. The
> > > DRAM initialization code is the mainly part that are not allowed to be
> > > open-sourced.
> > >
> > > The preloader has so many functions which are not easy to port to the
> > > U-Boot SPL.
> > > Assume all the codes are allowed to be open sourced.If all the functions
> > > are ported to SPL, the DM must be used in SPL, which will make the SPL
> > > binary too large to fit in the SRAM.If only the necessary parts are
> > > ported (e.g. DRAM initialization), the SPL will be incompatible with the
> > > BootROM and the FlashTool and the users will be in trouble recovering a
> > > board.
> > >
> > > At present the preloader can be downloaded from the Internet. Users can
> > > concentrate on the development without managing the low level parts.
> > >
> > > BTW, there are also chips use U-Boot as a second/third bootloader while
> > > using their proprietary binary as the first stage bootloader. For
> > > example the bcm7xxx.
> >
> > Thank you for your detailed explanation. I am not so concerned about
> > the short-term solution or older chips.
> >
> > A few questions:
> >
> > 1. Why can you not open-source the DRAM init code?
> > 2. You don't need to enable DM in SPL if that makes the size too big.
> >
> > This actually doesn't sound so different from the Rockchip situation,
> > and there it has been possible to have an open-source SPL. In fact it
> > does use DM although on some boards it uses of-platdata to remove
> > device-tree size. From the high quality of your patches it doesn't
> > seem like your team would need any help to do this, but I am happy to
> > help if that is useful.
> >
> > Anyway, we can go ahead with what you have and hopefully resolve this
> > in the future.
> >
> > Reviewed-by: Simon Glass <sjg at chromium.org>
> >
> > Regards,
> > Simon
>
>
> For the first question, it's not only about the dram init codes. MT7623
> used many components from a smart phone chip, which contains many
> security mechanisms like anti-debug and anti-clone which is protected
> by the company. The preloader will initialize them thus make it unable
> to be open-sourced.

I do feel this is confusing obscurity with security. If the system is
secure then it can be open-source. In fact it is probably better that
way (more eyes).

>
> For the rest questions, yes we always have ways to implement an
> source-source SPL to replace the preloader if at least essential source
> codes can be opened. The MT7623 actually uses technologies from old
> chips (e.g. the USB download). Current design can let the users upgrade
> their old u-boot seamlessly. For our newly designed chips, such as the
> MT7629 in this patch series, the SPL has already been used to replace
> the preloader. We removed USB download and other unnecessary parts and
> used full u-boot from the beginning. There is no compatibility issue for
> this chip.

I think you can start with a basic U-Boot SPL and add features over time.

>
> And again we thank for your kind help.

You are welcome. I encourage you to upstream more MediaTek platforms.

Regards,
Simon