[PATCH v2 1/6] reboot-mode: Use actual cell size instead of sizeof(u32)

[Sean Anderson]

On 2/13/26 06:27, Aswin Murugan wrote:
> The nvmem reboot-mode driver hardcodes sizeof(u32) for NVMEM read/write
> operations. This fails on platforms where the reboot reason storage is
> smaller than 4 bytes.
> 
> On Qualcomm platforms with single-byte PMIC register storage, attempting
> to read 4 bytes from a 1-byte cell causes the NVMEM subsystem to return
> -EINVAL, breaking reboot-mode functionality.
> 
> Replace sizeof(*mode) and sizeof(mode) with priv->cell.size to use the
> actual NVMEM cell size. Also initialize *mode to 0 in reboot_mode_get()
> to ensure a clean state for cells smaller than u32.
> 
> This allows the driver to work with cells of any size, from single bytes
> to multi-byte words.
> 
> Signed-off-by: Aswin Murugan <aswin.murugan at oss.qualcomm.com>
> ---
>   drivers/reboot-mode/reboot-mode-nvmem.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/reboot-mode/reboot-mode-nvmem.c b/drivers/reboot-mode/reboot-mode-nvmem.c
> index b9af242520a..60307cce49f 100644
> --- a/drivers/reboot-mode/reboot-mode-nvmem.c
> +++ b/drivers/reboot-mode/reboot-mode-nvmem.c
> @@ -18,15 +18,16 @@ struct nvmem_reboot_mode_priv {
>   static int reboot_mode_get(struct udevice *dev, u32 *mode)
>   {
>   	struct nvmem_reboot_mode_priv *priv = dev_get_priv(dev);
> +	*mode = 0;
>   
> -	return nvmem_cell_read(&priv->cell, mode, sizeof(*mode));
> +	return nvmem_cell_read(&priv->cell, mode, priv->cell.size);
>   }
>   
>   static int reboot_mode_set(struct udevice *dev, u32 mode)
>   {
>   	struct nvmem_reboot_mode_priv *priv = dev_get_priv(dev);
>   
> -	return nvmem_cell_write(&priv->cell, &mode, sizeof(mode));
> +	return nvmem_cell_write(&priv->cell, &mode, priv->cell.size);
>   }
>   
>   static const struct reboot_mode_ops nvmem_reboot_mode_ops = {

I'm not sure about this. drivers/power/reset/nvmem-reboot-mode.c in Linux
always writes sizeof(unsigned long), and this is checked against the nvmem
cell length in __nvmem_cell_entry_write. We should try to keep our behavior
close to Linux's.

--Sean