[PATCH] cmd: ums: Set Device Descriptor iSerial based on serial# env variable

[Łukasz Majewski]

On Sat, 13 Jun 2026 04:54:23 +0200
Marek Vasut <marex at nabladev.com> wrote:

> The DFU code currently sets the content of "serial#" environment
> variable into Device Descriptor iSerial field. This is useful when
> there are multiple devices connected to the same host PC and they
> have to be told apart. Replicate the same behavior in the UMS code.
> 
> Example without serial# set, which is the original behavior:
> "
> u-boot=> ums 0 mmc 1
> UMS: LUN 0, dev mmc 1, hwpart 0, sector 0x0, count 0x1d5a000
> 
> $ dmesg -w
> ...
> usb 5-2.3.7: New USB device found, idVendor=0525, idProduct=a4a5,
> bcdDevice=7e.a7 usb 5-2.3.7: New USB device strings: Mfr=1,
> Product=2, SerialNumber=0 usb 5-2.3.7: Product: USB download gadget
> usb 5-2.3.7: Manufacturer: Vendor
>                             <------------------------------- NOT HERE
> usb-storage 5-2.3.7:1.0: USB Mass Storage device detected
> ...
> 
> $ lsusb -vd 0525:a4a5
> 
> Bus 005 Device 051: ID 0525:a4a5 Netchip Technology, Inc. Linux-USB
> File-backed Storage Gadget Negotiated speed: High Speed (480Mbps)
> Device Descriptor:
>   bLength                18
>   bDescriptorType         1
>   bcdUSB               2.00
>   bDeviceClass            0 [unknown]
>   bDeviceSubClass         0 [unknown]
>   bDeviceProtocol         0
>   bMaxPacketSize0        64
>   idVendor           0x0525 Netchip Technology, Inc.
>   idProduct          0xa4a5 Linux-USB File-backed Storage Gadget
>   bcdDevice           7e.a7
>   iManufacturer           1 Vendor
>   iProduct                2 USB download gadget
>   iSerial                 0 <------------------------------- NOT HERE
> ...
> "
> 
> Example with serial# set to 1234abcd, which is the optional new
> behavior: "
> u-boot=> setenv serial# 1234abcd <------------------------------ HERE
> u-boot=> ums 0 mmc 1
> UMS: LUN 0, dev mmc 1, hwpart 0, sector 0x0, count 0x1d5a000
> 
> $ dmesg -w
> ...
> usb 5-2.3.7: New USB device found, idVendor=0525, idProduct=a4a5,
> bcdDevice=7e.a7 usb 5-2.3.7: New USB device strings: Mfr=1,
> Product=2, SerialNumber=3 usb 5-2.3.7: Product: USB download gadget
> usb 5-2.3.7: Manufacturer: Vendor
> usb 5-2.3.7: SerialNumber: 1234abcd <--------------------------- HERE
> usb-storage 5-2.3.7:1.0: USB Mass Storage device detected
> ...
> 
> $ lsusb -vd 0525:a4a5
> 
> Bus 005 Device 052: ID 0525:a4a5 Netchip Technology, Inc. Linux-USB
> File-backed Storage Gadget Negotiated speed: High Speed (480Mbps)
> Device Descriptor:
>   bLength                18
>   bDescriptorType         1
>   bcdUSB               2.00
>   bDeviceClass            0 [unknown]
>   bDeviceSubClass         0 [unknown]
>   bDeviceProtocol         0
>   bMaxPacketSize0        64
>   idVendor           0x0525 Netchip Technology, Inc.
>   idProduct          0xa4a5 Linux-USB File-backed Storage Gadget
>   bcdDevice           7e.a7
>   iManufacturer           1 Vendor
>   iProduct                2 USB download gadget
>   iSerial                 3 1234abcd <-------------------------- HERE
> ...
> "
> 
> Signed-off-by: Marek Vasut <marex at nabladev.com>
> ---
> Cc: Lukasz Majewski <lukma at nabladev.com>
> Cc: Mattijs Korpershoek <mkorpershoek at kernel.org>
> Cc: Simon Glass <sjg at chromium.org>
> Cc: Tom Rini <trini at konsulko.com>
> Cc: u-boot at lists.denx.de
> ---
>  cmd/usb_mass_storage.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/cmd/usb_mass_storage.c b/cmd/usb_mass_storage.c
> index e8b87045bdc..335258d7a56 100644
> --- a/cmd/usb_mass_storage.c
> +++ b/cmd/usb_mass_storage.c
> @@ -9,6 +9,7 @@
>  #include <blk.h>
>  #include <command.h>
>  #include <console.h>
> +#include <env.h>
>  #include <errno.h>
>  #include <g_dnl.h>
>  #include <malloc.h>
> @@ -65,7 +66,7 @@ static void ums_fini(void)
>  
>  static int ums_init(const char *devtype, const char
> *devnums_part_str) {
> -	char *s, *t, *devnum_part_str, *name;
> +	char *s, *t, *devnum_part_str, *name, *sn;
>  	struct blk_desc *block_dev;
>  	struct disk_partition info;
>  	int partnum;
> @@ -76,6 +77,12 @@ static int ums_init(const char *devtype, const
> char *devnums_part_str) if (!s)
>  		return -1;
>  
> +	if (CONFIG_IS_ENABLED(ENV_SUPPORT)) {
> +		sn = env_get("serial#");
> +		if (sn)
> +			g_dnl_set_serialnumber(sn);
> +	}
> +
>  	t = s;
>  	ums_count = 0;
>  

Reviewed-by: Łukasz Majewski <lukma at nabladev.com>

-- 
Best regards,

Lukasz Majewski

--
Nabla Software Engineering GmbH
HRB 40522 Augsburg
Phone: +49 821 45592596
E-Mail: office at nabladev.com
Managing Director : Stefano Babic