Hi Andre,
On 4/22/25 2:11 PM, Andre Przywara wrote:
On Tue, 22 Apr 2025 12:49:40 +0200
Quentin Schulz <quentin.sch...@cherry.de> wrote:
Hi,
Hi Andre and Yixun Lan,
On 4/21/25 11:29 PM, Andre Przywara wrote:
On Fri, 18 Apr 2025 13:28:23 +0200
Quentin Schulz <quentin.sch...@cherry.de> wrote:
Hi Quentin,
thanks for having a look!
Hi Andre,
On 4/17/25 2:05 AM, Andre Przywara wrote:
Some boards with Allwinner SoCs feature a "FEL" key, sometimes also
labelled "uboot", which triggers the BootROM FEL mode, when pressed upon
power-on or reset. This allows to access the SoC's memory via USB OTG,
and to upload and execute code. There is a tool to upload our U-Boot image
and immediately boot it, when the SoC is in FEL mode.
To mimic this convenient behaviour on boards without such a dedicated key,
we can query a GPIO pin very early in the SPL boot, then trigger the
BootROM FEL routine. There has not been much of a SoC or board setup at
this point, so we enter the BROM in a rather pristine state still. On
64-bit SoCs the required AArch32 reset guarantees a clean CPU state anyway.
Any GPIO can be used for that, the signal is expected to be active low,
consequently we enable the pull-up resistors for that pin. A board (or a
user) is expected to specify the GPIO name using the
CONFIG_SUNXI_FAKE_FEL_PIN Kconfig variable. When this variable is not set,
the compiler will optimise away the call.
Call the code first thing in board_init_f(), which is the first sunxi
specific C routine.
Signed-off-by: Andre Przywara <andre.przyw...@arm.com>
---
arch/arm/mach-sunxi/Kconfig | 10 ++++++++++
arch/arm/mach-sunxi/board.c | 31 +++++++++++++++++++++++++++++++
2 files changed, 41 insertions(+)
diff --git a/arch/arm/mach-sunxi/Kconfig b/arch/arm/mach-sunxi/Kconfig
index ab432390d3c..f1cfdb548bc 100644
--- a/arch/arm/mach-sunxi/Kconfig
+++ b/arch/arm/mach-sunxi/Kconfig
@@ -825,6 +825,16 @@ config USB3_VBUS_PIN
---help---
See USB1_VBUS_PIN help text.
+config SUNXI_FAKE_FEL_PIN
+ string "fake FEL GPIO pin"
+ default ""
+ ---help---
+ Define a GPIO that shall force entering FEL mode when a button
+ connected to this pin is pressed at boot time. This must be an
+ active low signal, the internal pull-up resistors are activated.
+ This takes a string in the format understood by sunxi_name_to_gpio,
+ e.g. PH1 for pin 1 of port H.
+
Why not use the DT for that? Then you wouldn't even need to assume the
polarity of the signal or whether pull-up/downs need to be activated, etc.
As Yixun Lan already pointed out, the DT is not available at this
point, and doing several pull-ups to get this information from the DT
into the SPL image are really over the top for this purpose.
OK, we do have something "similar" for Rockchip boards, via the
sysreset-gpio DT property in /config, see
arch/arm/mach-rockchip/rk3399/rk3399.c and
arch/arm/dts/rk3399-puma-haikou-u-boot.dtsi.
I guess something similar could be implemented IFF there's an actual DT
in SPL (or even TPL). We for sure have DT in SPL for most if not all
Rockchip devices, and probably in TPL as well. Hence why I sometimes
forget other Arm boards may not have DT in those stages :)
Yeah, I know, there is some push for DT anywhere, but it would be quite
some pain for sunxi, for very little benefit. We are very tight in the SPL
code size for some SoCs, up to the point where for instance enabling this
code here made the build break on some SoCs (I found something to free
some code space elsewhere, might send that later). So pulling libfdt and
DM code in would require going TPL, I guess. But I don't see the reason,
We are also very limited on some Rockchip SoCs, see PX30 which has a TPL
without DM support and where adding a printf (there are already some) is
sometimes too much to fit into the SRAM, so I understand. We do have
some other SoCs that have DM enabled in TPL, e.g. RK3399 imply it.
really, as I tend to see the SPL more as the continuation of the BootROM,
which manages without board specific knowledge at all. And for the small
bits of info we need, we can happily use Kconfig. Most of it is actually
SoC specific, not board specific, so users don't get bothered normally,
and it just works (TM).
Jonas has started to support "generic" images for Rockchip boards based
on the recommended hardware design specified by Rockchip themselves.
Most companies do mostly respect it, so that seems to be working quite
nicely.
Depending on what exactly you want to support with U-Boot, a DM-less SPL
may be difficult. e.g. if you want to support a fallback storage medium
for loading u-boot.itb (or proper, don't know what's being used on
Allwinner) that differs from the one used to load the SPL by the
BootROM, then you possibly cannot rely on the BootROM initializing the
PHYs, controllers, pinmuxes and pinconfs. KConfig may be usable for this
but that will make things cumbersome to support.
There is tons of work and cleanup to do on the sunxi side, and were
already have quite some backlog, so I want to avoid introducing more
construction sites.
Fair, it also doesn't mean that what's currently added cannot be
migrated later on :)
[...]
You can have the property in the -u-boot.dtsi then if you want?
While the FEL button on the X96 is "fake", it does what it says, just in
software, maybe that is close enough to "hardware definition" which
would make it suitable for the DT (well, we also store binman nodes in
Yes, I have a patch to add this particular button as a GPIO button into
the DT, so people can use it for whatever they want in Linux (trigger
reboot, update, you name it). But this is rather orthogonal to this
problem, as mentioned above.
Mmmmm but this will be in the Linux kernel DT and I assume you want the
same GPIO to be used in U-Boot and in Linux, so it would probably be
best to make sure they stay in sync? How are you planning to do that?
On the Allwinner side we were syncing the DTs regularly for years already,
and had no conflicting or different bindings at all. So I prefer to think
of "the DT", with Linux or U-Boot just carrying slightly different
versions for some time.
If the kernel DTB is coming from U-Boot, it should be much less
difficult to keep this synced. But if it isn't, you would need to patch
it live before booting the kernel for example.
In any case, I think the conclusion is that DT cannot be used (yet?) for
that so this thread is now essentially just me being curious :)
Cheers,
Quentin
