[PATCH] arm: mach-snapdragon: pinctrl: Place pin_name in .data section

[Ramon Fried]

On Mon, Jul 5, 2021 at 3:19 PM Stephan Gerhold <stephan at gerhold.net> wrote:
>
> According to arch/arm/lib/crt0_64.S, the BSS section is "UNAVAILABLE"
> and uninitialized before relocation. Also, it overlaps with the
> appended DTB before relocation, so writing data into a variable
> in the BSS section might corrupt the appended DTB.
>
> Unfortunately, pinctrl-apq8016.c and pinctrl-apq8096.c do place the
> "pin_name" variable in the BSS section (since it's uninitialized).
> It's also used before relocation, when setting up the pinctrl for
> the serial driver.
>
> On DB410c this causes "GPIO_5" to be written into some part of an
> appended DTB, e.g.:
>
> 80111820: edfe0dd0 9f100000 38000000 c00e0000    ...........8....
> 80111830: 28000000 11000000 10000000 00000000    ...(............
> 80111840: 4f495047 8800355f 00000000 00000000    GPIO_5..........
> 80111850: 00000000 00000000 01000000 00000000    ................
> 80111860: 03000000 04000000 00000000 02000000    ................
> 80111870: 03000000 04000000 0f000000 02000000    ................
> 80111880: 03000000 2d000000 1b000000 6c617551    .......-....Qual
> 80111890: 6d6d6f63 63655420 6c6f6e68 6569676f    comm Technologie
>
> Depending on the part of the DTB that is corrupted this might not
> cause any problems, but it can also result in strange reboots
> without any serial output.
>
> Fortunately, in practice this does not cause issues on DB410c yet
> because board_fdt_blob_setup() in dragonboard410c.c currently
> overrides the appended DTB with the one passed by the previous
> bootloader (LK) (which does not get corrupted).
>
> DB820c does not have board_fdt_blob_setup() so I would expect it to
> be affected by this problem. Perhaps everyone was just fortunate to
> not compile an U-Boot configuration where the pin_name corrupts an
> important part of the DTB.
>
> Make sure "pin_name" is explicitly placed in the .data section
> instead of .bss to fix this.
>
> Cc: Ramon Fried <rfried.dev at gmail.com>
> Signed-off-by: Stephan Gerhold <stephan at gerhold.net>
> ---
>
>  arch/arm/mach-snapdragon/pinctrl-apq8016.c | 3 +--
>  arch/arm/mach-snapdragon/pinctrl-apq8096.c | 2 +-
>  2 files changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm/mach-snapdragon/pinctrl-apq8016.c b/arch/arm/mach-snapdragon/pinctrl-apq8016.c
> index 1042b564c3..70c0be0bca 100644
> --- a/arch/arm/mach-snapdragon/pinctrl-apq8016.c
> +++ b/arch/arm/mach-snapdragon/pinctrl-apq8016.c
> @@ -10,7 +10,7 @@
>  #include <common.h>
>
>  #define MAX_PIN_NAME_LEN 32
> -static char pin_name[MAX_PIN_NAME_LEN];
> +static char pin_name[MAX_PIN_NAME_LEN] __section(".data");
>  static const char * const msm_pinctrl_pins[] = {
>         "SDC1_CLK",
>         "SDC1_CMD",
> @@ -59,4 +59,3 @@ struct msm_pinctrl_data apq8016_data = {
>         .get_function_mux = apq8016_get_function_mux,
>         .get_pin_name = apq8016_get_pin_name,
>  };
> -
> diff --git a/arch/arm/mach-snapdragon/pinctrl-apq8096.c b/arch/arm/mach-snapdragon/pinctrl-apq8096.c
> index 20a71c319b..45462f01c2 100644
> --- a/arch/arm/mach-snapdragon/pinctrl-apq8096.c
> +++ b/arch/arm/mach-snapdragon/pinctrl-apq8096.c
> @@ -10,7 +10,7 @@
>  #include <common.h>
>
>  #define MAX_PIN_NAME_LEN 32
> -static char pin_name[MAX_PIN_NAME_LEN];
> +static char pin_name[MAX_PIN_NAME_LEN] __section(".data");
>  static const char * const msm_pinctrl_pins[] = {
>         "SDC1_CLK",
>         "SDC1_CMD",
> --
> 2.32.0
>
Reviewed-by: Ramon Fried <rfried.dev at gmail.com>