Re: [PATCH 06/19] thunderbolt: Try reading host DROM from device tree first

[Mika Westerberg <mika.westerberg@linux.intel.com>]

Hi,

On Sun, Aug 30, 2026 at 10:19:24PM +0200, Sven Peter wrote:
> On Apple Silicon SoCs the DROM is provided by a device tree property.
> Try reading from that property first.
> 
> Signed-off-by: Sven Peter <sven@kernel.org>
> ---
>  drivers/thunderbolt/eeprom.c | 32 +++++++++++++++++++++++++++-----
>  1 file changed, 27 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/thunderbolt/eeprom.c b/drivers/thunderbolt/eeprom.c
> index 2a13fa6888ba..389de7df84f6 100644
> --- a/drivers/thunderbolt/eeprom.c
> +++ b/drivers/thunderbolt/eeprom.c
> @@ -468,14 +468,14 @@ static void tb_switch_drom_free(struct tb_switch *sw)
>  }
>  
>  /*
> - * tb_drom_copy_efi - copy drom supplied by EFI to sw->drom if present
> + * tb_drom_copy_property - copy drom from a device property if present

tb_drom_copy_property() - Copy DROM from ..

Ditto for the other kernel-doc comments. If it is static trivial function
you don't need to add them.

>   */
> -static int tb_drom_copy_efi(struct tb_switch *sw, u16 *size)
> +static int tb_drom_copy_property(struct tb_switch *sw, const char *name, u16 *size)

I think this should be split into two lines.

>  {
>  	struct device *dev = sw->tb->nhi->dev;
>  	int len, res;
>  
> -	len = device_property_count_u8(dev, "ThunderboltDROM");
> +	len = device_property_count_u8(dev, name);
>  	if (len < 0 || len < sizeof(struct tb_drom_header))
>  		return -EINVAL;
>  
> @@ -483,8 +483,7 @@ static int tb_drom_copy_efi(struct tb_switch *sw, u16 *size)
>  	if (res)
>  		return res;
>  
> -	res = device_property_read_u8_array(dev, "ThunderboltDROM", sw->drom,
> -									len);
> +	res = device_property_read_u8_array(dev, name, sw->drom, len);
>  	if (res)
>  		goto err;
>  
> @@ -500,6 +499,22 @@ static int tb_drom_copy_efi(struct tb_switch *sw, u16 *size)
>  	return -EINVAL;
>  }
>  
> +/*
> + * tb_drom_copy_of_apple - copy drom supplied by the device tree for Apple Silicon to sw->drom.

Like these, not really useful comments you can drop.

> + */
> +static int tb_drom_copy_of_apple(struct tb_switch *sw, u16 *size)
> +{
> +	return tb_drom_copy_property(sw, "apple,thunderbolt-drom", size);
> +}
> +
> +/*
> + * tb_drom_copy_efi - copy drom supplied by EFI to sw->drom if present
> + */
> +static int tb_drom_copy_efi(struct tb_switch *sw, u16 *size)
> +{
> +	return tb_drom_copy_property(sw, "ThunderboltDROM", size);
> +}
> +
>  static int tb_drom_copy_nvm(struct tb_switch *sw, u16 *size)
>  {
>  	u16 drom_offset;
> @@ -675,6 +690,13 @@ static int tb_drom_host_read(struct tb_switch *sw)
>  {
>  	u16 size;
>  
> +	/*
> +	 * Apple Silicon machines always get their host DROM from the Device Tree,
> +	 * so make sure to try reading it first before any other method.
> +	 */
> +	if (!tb_drom_copy_of_apple(sw, &size))
> +		return tb_drom_parse(sw, size);
> +
>  	if (tb_switch_is_usb4(sw)) {
>  		usb4_switch_read_uid(sw, &sw->uid);
>  		if (!usb4_copy_drom(sw, &size))
> 
> -- 
> 2.55.0
>