[PATCH] sunxi: add "fake" FEL pin support

[PATCH] sunxi: add "fake" FEL pin support

[Andre Przywara]

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, and 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.przywara@arm.com>
---
 arch/arm/mach-sunxi/Kconfig |  9 +++++++++
 arch/arm/mach-sunxi/board.c | 30 ++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/arch/arm/mach-sunxi/Kconfig b/arch/arm/mach-sunxi/Kconfig
index 25b47ada7ad..912d3a3a650 100644
--- a/arch/arm/mach-sunxi/Kconfig
+++ b/arch/arm/mach-sunxi/Kconfig
@@ -789,6 +789,15 @@ config MMC_SUNXI_SLOT_EXTRA
 	slot or emmc on mmc1 - mmc3. Setting this to 1, 2 or 3 will enable
 	support for this.
 
+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 takes a string in the format understood by sunxi_name_to_gpio,
+	e.g. PH1 for pin 1 of port H.
+
 config I2C0_ENABLE
 	bool "Enable I2C/TWI controller 0"
 	default y if MACH_SUN4I || MACH_SUN5I || MACH_SUN7I || MACH_SUN8I_R40
diff --git a/arch/arm/mach-sunxi/board.c b/arch/arm/mach-sunxi/board.c
index 701899ee4b2..ea0e7bb381d 100644
--- a/arch/arm/mach-sunxi/board.c
+++ b/arch/arm/mach-sunxi/board.c
@@ -457,8 +457,38 @@ u32 spl_mmc_boot_mode(struct mmc *mmc, const u32 boot_device)
 	return result;
 }
 
+static void check_fake_fel_button(void)
+{
+	u32 brom_entry = 0x20;
+	int pin, value, mux;
+
+	/* check for empty string at compile time */
+	if (sizeof(CONFIG_SUNXI_FAKE_FEL_PIN) == sizeof(""))
+		return;
+
+	pin = sunxi_name_to_gpio(CONFIG_SUNXI_FAKE_FEL_PIN);
+	if (pin < 0)
+		return;
+
+	mux = sunxi_gpio_get_cfgpin(pin);
+	sunxi_gpio_set_cfgpin(pin, SUNXI_GPIO_INPUT);
+	value = gpio_get_value(pin);
+	sunxi_gpio_set_cfgpin(pin, mux);
+
+	if (value)
+		return;
+
+	/* Older SoCs maps the BootROM high in the address space. */
+	if (fel_stash.sctlr & BIT(13))
+		brom_entry |= 0xffff0000;
+
+	return_to_fel(0, brom_entry);
+}
+
 void board_init_f(ulong dummy)
 {
+	check_fake_fel_button();
+
 	sunxi_sram_init();
 
 	/* Enable non-secure access to some peripherals */
-- 
2.46.3

Re: [PATCH] sunxi: add "fake" FEL pin support

[Yixun Lan]

Hi Andre Przywara:

I can understand the motivation behind this patch, which
I think it's a good addition to BROM FEL mode..

On 00:59 Wed 09 Apr     , 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, and 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.
> 
is it possible to provide a dts interface to specify the gpio pin?
it would be more convenient, but a CONFIG option would be fine..

> Call the code first thing in board_init_f(), which is the first sunxi
> specific C routine.
> 
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> ---
>  arch/arm/mach-sunxi/Kconfig |  9 +++++++++
>  arch/arm/mach-sunxi/board.c | 30 ++++++++++++++++++++++++++++++
>  2 files changed, 39 insertions(+)
> 
> diff --git a/arch/arm/mach-sunxi/Kconfig b/arch/arm/mach-sunxi/Kconfig
> index 25b47ada7ad..912d3a3a650 100644
> --- a/arch/arm/mach-sunxi/Kconfig
> +++ b/arch/arm/mach-sunxi/Kconfig
> @@ -789,6 +789,15 @@ config MMC_SUNXI_SLOT_EXTRA
>  	slot or emmc on mmc1 - mmc3. Setting this to 1, 2 or 3 will enable
>  	support for this.
>  
> +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 takes a string in the format understood by sunxi_name_to_gpio,
> +	e.g. PH1 for pin 1 of port H.
> +
>  config I2C0_ENABLE
>  	bool "Enable I2C/TWI controller 0"
>  	default y if MACH_SUN4I || MACH_SUN5I || MACH_SUN7I || MACH_SUN8I_R40
> diff --git a/arch/arm/mach-sunxi/board.c b/arch/arm/mach-sunxi/board.c
> index 701899ee4b2..ea0e7bb381d 100644
> --- a/arch/arm/mach-sunxi/board.c
> +++ b/arch/arm/mach-sunxi/board.c
> @@ -457,8 +457,38 @@ u32 spl_mmc_boot_mode(struct mmc *mmc, const u32 boot_device)
>  	return result;
>  }
>  
> +static void check_fake_fel_button(void)
> +{
> +	u32 brom_entry = 0x20;
> +	int pin, value, mux;
> +
> +	/* check for empty string at compile time */
> +	if (sizeof(CONFIG_SUNXI_FAKE_FEL_PIN) == sizeof(""))
> +		return;
> +
> +	pin = sunxi_name_to_gpio(CONFIG_SUNXI_FAKE_FEL_PIN);
> +	if (pin < 0)
> +		return;
> +
> +	mux = sunxi_gpio_get_cfgpin(pin);
> +	sunxi_gpio_set_cfgpin(pin, SUNXI_GPIO_INPUT);
> +	value = gpio_get_value(pin);
> +	sunxi_gpio_set_cfgpin(pin, mux);
> +
> +	if (value)
> +		return;
so will skip EFL mode when "GPIO == 1" (which means gpio high level)?
maybe we should document in the Kconfig help section:
 setting GPIO low to enter FEL mode
or even great if the gpio can be configurable for FEL mode

> +
> +	/* Older SoCs maps the BootROM high in the address space. */
> +	if (fel_stash.sctlr & BIT(13))
> +		brom_entry |= 0xffff0000;
> +
> +	return_to_fel(0, brom_entry);
> +}
> +
>  void board_init_f(ulong dummy)
>  {
> +	check_fake_fel_button();
> +
>  	sunxi_sram_init();
>  
>  	/* Enable non-secure access to some peripherals */
> -- 
> 2.46.3
> 

-- 
Yixun Lan (dlan)
Gentoo Linux Developer
GPG Key ID AABEFD55

Re: [PATCH] sunxi: add "fake" FEL pin support

[Andre Przywara]

On Wed, 9 Apr 2025 02:23:03 +0000
Yixun Lan <dlan@gentoo.org> wrote:

Hi,

> I can understand the motivation behind this patch, which
> I think it's a good addition to BROM FEL mode..

Thanks for having a look!

> On 00:59 Wed 09 Apr     , 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, and 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.
> >   
> is it possible to provide a dts interface to specify the gpio pin?
> it would be more convenient, but a CONFIG option would be fine..

That wouldn't really help here, since this patch is SPL only, and we have
no DT there. And it must be in the SPL, because otherwise we cannot easily
trigger the RMR reset, we need to be in EL3 for that.

Besides, I imagine this also as a hacker option, where I just specify this
GPIO temporarily, for development, and just bridge two pins on the headers
with a screwdriver or so ;-)

The X96 Mate box has an actual switch connected to PH9, and it's meant
to be the FEL button, so I have a DT patch to describe this as a button,
but this is in addition to this patch here.

> > Call the code first thing in board_init_f(), which is the first sunxi
> > specific C routine.
> > 
> > Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> > ---
> >  arch/arm/mach-sunxi/Kconfig |  9 +++++++++
> >  arch/arm/mach-sunxi/board.c | 30 ++++++++++++++++++++++++++++++
> >  2 files changed, 39 insertions(+)
> > 
> > diff --git a/arch/arm/mach-sunxi/Kconfig b/arch/arm/mach-sunxi/Kconfig
> > index 25b47ada7ad..912d3a3a650 100644
> > --- a/arch/arm/mach-sunxi/Kconfig
> > +++ b/arch/arm/mach-sunxi/Kconfig
> > @@ -789,6 +789,15 @@ config MMC_SUNXI_SLOT_EXTRA
> >  	slot or emmc on mmc1 - mmc3. Setting this to 1, 2 or 3 will enable
> >  	support for this.
> >  
> > +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 takes a string in the format understood by sunxi_name_to_gpio,
> > +	e.g. PH1 for pin 1 of port H.
> > +
> >  config I2C0_ENABLE
> >  	bool "Enable I2C/TWI controller 0"
> >  	default y if MACH_SUN4I || MACH_SUN5I || MACH_SUN7I || MACH_SUN8I_R40
> > diff --git a/arch/arm/mach-sunxi/board.c b/arch/arm/mach-sunxi/board.c
> > index 701899ee4b2..ea0e7bb381d 100644
> > --- a/arch/arm/mach-sunxi/board.c
> > +++ b/arch/arm/mach-sunxi/board.c
> > @@ -457,8 +457,38 @@ u32 spl_mmc_boot_mode(struct mmc *mmc, const u32 boot_device)
> >  	return result;
> >  }
> >  
> > +static void check_fake_fel_button(void)
> > +{
> > +	u32 brom_entry = 0x20;
> > +	int pin, value, mux;
> > +
> > +	/* check for empty string at compile time */
> > +	if (sizeof(CONFIG_SUNXI_FAKE_FEL_PIN) == sizeof(""))
> > +		return;
> > +
> > +	pin = sunxi_name_to_gpio(CONFIG_SUNXI_FAKE_FEL_PIN);
> > +	if (pin < 0)
> > +		return;
> > +
> > +	mux = sunxi_gpio_get_cfgpin(pin);
> > +	sunxi_gpio_set_cfgpin(pin, SUNXI_GPIO_INPUT);
> > +	value = gpio_get_value(pin);
> > +	sunxi_gpio_set_cfgpin(pin, mux);
> > +
> > +	if (value)
> > +		return;  
> so will skip EFL mode when "GPIO == 1" (which means gpio high level)?
> maybe we should document in the Kconfig help section:
>  setting GPIO low to enter FEL mode
> or even great if the gpio can be configurable for FEL mode

Yes, it assumes to be active low, which I think is the common
configuration. I should probably activate the pull ups on the way, and
indeed document this. Thanks for the heads up!

As for a CONFIG option: yes, I thought about that, but wanted to see if we
really need that. So happy to add this when a user shows up who needs it.

Cheers,
Andre


> > +
> > +	/* Older SoCs maps the BootROM high in the address space. */
> > +	if (fel_stash.sctlr & BIT(13))
> > +		brom_entry |= 0xffff0000;
> > +
> > +	return_to_fel(0, brom_entry);
> > +}
> > +
> >  void board_init_f(ulong dummy)
> >  {
> > +	check_fake_fel_button();
> > +
> >  	sunxi_sram_init();
> >  
> >  	/* Enable non-secure access to some peripherals */
> > -- 
> > 2.46.3
> >   
>