[U-Boot] [PATCH 2/9] sunxi: Move SPL s_init() code to board_init_f()

[Siarhei Siamashka <siarhei.siamashka@gmail.com>]

On Mon, 29 Dec 2014 09:15:36 -0700
Simon Glass <sjg@chromium.org> wrote:

> Hi Ian,
> 
> On 28 December 2014 at 02:19, Ian Campbell <ijc@hellion.org.uk> wrote:
> > On Tue, 2014-12-23 at 12:04 -0700, Simon Glass wrote:
> >
> >> +void board_init_f(ulong dummy)
> >> +{
> > [...]
> >> +     /* Clear the BSS. */
> >> +     memset(__bss_start, 0, __bss_end - __bss_start);
> >> +
> >> +     board_init_r(NULL, 0);
> >
> > The previous (__weak) version of board_init_f also sets gd, which you've
> > also removed from s_init here and not added back anywhere (indeed, this
> > is the point...). But where is gd initialised now?
> 
> It's still in start.S, I've just removed this duplicate.
> 
> >
> > The patch generally looks good, two quick questions: has it been tested
> > in both FEL and regular mode, and has it been tested with a "legacy" as
> > well as a driver model system? (I might be able to find time in a day or
> > two to answer these myself, but for now I'll just ask).
> 
> I haven't tried FEL, I only just heard of it in your email. I'll see
> if I can figure out how to test that.

Just like Ian suspected, this patch has messed up the FEL boot mode
support.

In a nutshell, FEL is a special USB protocol (accessible on a USB OTG
connector), which is implemented by the boot ROM and activated by
holding a special hardware button pressed and rebooting the device.
FEL supports commands to read/write device RAM and execute code on
the device. It is designed for device unbricking and firmware recovery.

In particular, the FEL boot mode support is very useful for debugging
u-boot and kernel problems on tablets (the SD card slot can be used
for the UART console, while the system is booted over a micro-USB cable
with the help of FEL):
    http://linux-sunxi.org/File:MSI_Primo81_and_MicroSD_breakout.jpg

In u-boot it is used in the following way:
 1. The SPL code is uploaded from the linux PC to the device SRAM via
    a FEL command (using the 'fel' program from sunxi-tools).
 2. The SPL code is executed via a FEL command and expected to
    initialize the DRAM controller. The code is executed as a
    normal C or assembly function, which needs to return control
    back to the BROM code when it is done. Right now this
    function is s_init().
 3. As the DRAM is initialized and available now, the main u-boot
    binary is now uploaded to DRAM via FEL. Together with boot.scr,
    the kernel, the dtb file and optionally initramfs as needed.
 4. The main u-boot binary is executed via a FEL command, but never
    returns back to BROM anymore.

More details are available in the linux-sunxi wiki:
    http://linux-sunxi.org/FEL
    http://linux-sunxi.org/FEL/Protocol
    http://linux-sunxi.org/FEL/USBBoot

I have submitted a patch to fix this regression:
    https://patchwork.ozlabs.org/patch/434826/

If you encounter problems and/or need help when testing FEL, please
let me know.

-- 
Best regards,
Siarhei Siamashka