[U-Boot] [PATCH 22/23] x86: Add some documentation on how to port U-Boot on x86

[Bin Meng <bmeng.cn@gmail.com>]

Hi Simon,

On Tue, Jan 27, 2015 at 9:23 AM, Simon Glass <sjg@chromium.org> wrote:
> Some information has been gleaned on tools and procedures for porting
> U-Boot to different x86 platforms. Add a few notes to start things off.
>
> Signed-off-by: Simon Glass <sjg@chromium.org>
> ---
>

Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

A minor comment below.

>  doc/README.x86 | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 63 insertions(+)
>
> diff --git a/doc/README.x86 b/doc/README.x86
> index 809a291..0e4628a 100644
> --- a/doc/README.x86
> +++ b/doc/README.x86
> @@ -164,6 +164,69 @@ mtrr - List and set the Memory Type Range Registers (MTRR). These are used to
>          mode to use. U-Boot sets up some reasonable values but you can
>          adjust then with this command.
>
> +Development Flow
> +----------------
> +
> +These notes are for those who want to port U-Boot to a new x86 platform.
> +
> +Since x86 CPUs boot from SPI flash, a SPI flash emulator is a good investment.
> +The Dediprog em100 can be used on Linux. The em100 tool is available here:
> +
> +   http://review.coreboot.org/p/em100.git
> +
> +On Minnowboard Max the following command line can be used:
> +
> +   sudo em100 -s -p LOW -d u-boot.rom -c W25Q64DW -r
> +
> +A suitable clip for connecting over the SPI flash chip is here:
> +
> +   http://www.dediprog.com/pd/programmer-accessories/EM-TC-8
> +
> +This allows you to override the SPI flash contents for development purposes.
> +Typically you can write to the em100 in around 1200ms, considerably faster
> +than programming the real flash device each time. The only important
> +limitation of the em100 is that it only supports SPI bus speeds up to 20MHz.
> +This means that images must be set to boot with that speed (Intel-specific
> +feature).
> +

It would be better to document what this Intel-specific feature is in
order to support this SPI bus frequency.

> +If your chip/board uses an Intel Firmware Support Package (FSP) it is fairly
> +easy to fit it in. You can follow the Minnowboard Max implementation, for
> +example. Hopefully you will just need to create new files similar to those
> +in arch/x86/cpu/baytrail which provide Bay Trail support.
> +
> +If you are not using an FSP you have more freedom and more responsibility.
> +The ivybridge support works this way, although it still uses a ROM for
> +graphics and still has binary blobs containing Intel code. You should aim to
> +support all important peripherals on your platform including video and storage.
> +Use the device tree for configuration where possible.
> +
> +For the microcode you can create a suitable device tree file using the
> +microcode tool:
> +
> +  ./tools/microcode-tool -d microcode.dat create <model>
> +
> +or if you only have header files and not the full Intel microcode.dat database:
> +
> +  ./tools/microcode-tool -H BAY_TRAIL_FSP_KIT/Microcode/M0130673322.h \
> +       -H BAY_TRAIL_FSP_KIT/Microcode/M0130679901.h \
> +       create all
> +
> +These are written to arch/x86/dts/microcode/ by default.
> +
> +Note that it is possible to just add the micrcode for your CPU if you know its
> +model. U-Boot prints this information when it starts
> +
> +   CPU: x86_64, vendor Intel, device 30673h
> +
> +so here we can use the M0130673322 file.
> +
> +If you platform can display POST codes on two little 7-segment displays on
> +the board, then you can use post_code() calls from C or assembler to monitor
> +boot progress. This can be good for debugging.
> +
> +If not, you can try to get serial working as early as possible. The early
> +debug serial port may be useful here. See setup_early_uart() for an example.
> +
>  TODO List
>  ---------
>  - Audio
> --

Regards,
Bin