The U-Boot "stemmy" board is mainly intended to simplify booting
mainline Linux on various smartphones from Samsung based on ST-Ericsson
Ux500. While the mainline kernel is working great, there are still some
features missing there. In particular, it is currently not possible to
charge the battery when using the mainline kernel.
This means that it is still necessary to boot the downstream/vendor
kernel from Samsung sometimes to charge the device. That kernel is
ancient, still uses board files + ATAGS instead of device trees and
relies on a strange very long kernel command line hardcoded in the
Samsung bootloader.
Actually, since mainline is booted with device trees there is a very
simple way to make the old downstream kernel work as well: We can
simply take most of the ATAGS passed to U-Boot from the Samsung
bootloader and copy them as-is when booting a kernel without device
tree. That way the long command line and other needed ATAGS are copied
as-is without having to bother with them.
The only exception is the ATAG_INITRD - since the initrd is loaded
by U-Boot, the atag for that should be generated in U-Boot so it points
to the correct address. All other ATAGS are copied as-is and not
generated in U-Boot.
Also use the chance and provide a serial# for U-Boot by parsing the
ATAG_SERIAL that is also passed by the Samsung bootloader.
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
At the moment the "stemmy" board attempts to detect the RAM size with
a simple memory test (get_ram_size()). Unfortunately, this does not work
correctly for devices with 768 MiB RAM (e.g. Samsung Galaxy Ace 2
(GT-I8160), "codina"). Reading/writing memory after the 768 MiB RAM
succeeds but actually overwrites some earlier parts of the memory.
For U-Boot this does not result in any major problems, but on Linux
this will eventually lead to strange crashes because of the memory
corruption.
Since the "stemmy" U-Boot port is designed to be chainloaded from
the original Samsung bootloader, the most reliable way to get the
available amount of RAM is to look at the ATAGS passed by the Samsung
bootloader. Fortunately, the header used to generate ATAGS in U-Boot
(asm/setup.h) can also be easily used to parse them.
Also clarify and simplify stemmy.h a bit to make it more clear where
some of the magic values in there are actually coming from.
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
The ST-Ericsson U8500 SoC has been used in mass-production for
some Android smartphones released around 2012.
In particular, Samsung has released more than 5 different
smartphones based on U8500, e.g.
- Samsung Galaxy S III mini (GT-I8190) "golden"
- Samsung Galaxy S Advance (GT-I9070) "janice"
- Samsung Galaxy Xcover 2 (GT-S7710) "skomer"
and a few others.
Mainline Linux has great support for the Ux500 SoC, so these
smartphones can also run Linux mainline quite well.
Unfortunately, the original Samsung bootloader used on these devices
has limitations that prevent booting Linux mainline directly.
It keeps the L2 cache enabled, which causes Linux to crash very early,
shortly after decompressing the kernel.
Using U-Boot allows to circumvent these limitations. We can let the
Samsung bootloader chain-load U-Boot and U-Boot locks the L2 cache
before booting into Linux. U-Boot has several other advantages
- it supports device-trees directly and we are no longer limited to
flashing Android boot images through Samsung's proprietary download
mode.
The Samsung "stemmy" board covers all Samsung devices based on U8500.
Add minimal support for "stemmy". For now only UART is supported but
this will be extended later.
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
The NovaThor U8500 SoC was released by ST-Ericsson in 2011.
It was used for some development boards like the CALAO Systems
Snowball SBC, but mass production was primarily for Android
smartphones like the Samsung Galaxy S III mini.
Previous support for U8500 was removed in
commit 68282f55b8 ("arm: Remove unused ST-Ericsson u8500 arch")
since none of the boards were converted to generic boards
before the deadline.
The new code does not have much in common with the previous code.
I have completely rewritten everything, embracing the Driver Model
and device trees wherever possible.
The U8500 support is a bit more minimal for now - my primary
use case is to use U-Boot as alternative bootloader for some of the
U8500 Samsung smartphones. At the moment U-Boot is chain-loaded from
the original Samsung bootloader. A side effect of this is that we
can (temporarily) get away without implementing some functionality
- e.g. all clocks are already enabled by the original bootloader.
More functionality will be added in future patches.
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: John Rigby <john.rigby@linaro.org>
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
