Re: [PATCH] crypto: atmel-sha204a - Fix OTP sysfs read and error handling

[Lothar Rubusch]

Hi Thorsten!

I tried to verify your patch on hardware today, unfortunately it did
not work for me.

My setup works with current atsha204a module in the below described way. When
trying to dump the OTP zone on exactly the same hardware with a patched module,
it only prints '0' and nothing more, see below.

Pls, let me know, if I'm doing something wrong; if my usage is wrong or
if my approach is somehow flaky. Otherwise, could you please have a second
look at it? Note, my patch at the time emerged from a particular
use-case at work, it's
likely that it's not covering all OTP. So, if incomplete, I'd really
appreciate having it fixed.

In the following I provide some details on what I did today.

8<-------------------------------------------------------------->8
My lab DUT hardware:
- RPi 3b+ with an ATSHA204A shield via i2c, 3.3V
- ATSHA204a with a locked config; initialized OTP zone with some values
- Just enough to be readable i.e. verify OTP content

My kernel source base, since on a RPi v6.19 branch, built w/ aarch64.
Note, I'm building the module then out-of-source with a separate .dtsi
(I'm not showing all the boiler-plate stuff here).
$ git remote -v
  origin  https://github.com/raspberrypi/linux (fetch)
  origin  https://github.com/raspberrypi/linux (push)
$ git log --oneline -3
  e150a7a6d683 (HEAD -> rpi-6.19.y, origin/rpi-6.19.y) configs: enable
Si5351 i2c common clock driver
  3c957f9e74de pcie-brcmstb: move the unilateral disable of CLKREQ#
before link-up
  994331c6ea59 drivers: media: pispbe: Add V4L2_PIX_FMT_NV12MT_COL128
format support

>From the bootlog
  ...
  [    0.000000][    T0] Kernel command line: coherent_pool=1M
8250.nr_uarts=1 snd_bcm2835.enable_headphones=0 cgroup_disable=memory
   bcm2708_fb.fbwidth=720 bcm2708_fb.fbheight=480 bcm2708_fb.fbswap=1
vc_mem.mem_base=0x3ec00000 vc_mem.mem_size=0x40000000  dwc_otg
  .lpm_enable=0 console=ttyAMA0,115200 console=tty1
root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline fsck.repair=yes
rootwait
  [    0.000000][    T0] cgroup: Disabling memory control group subsystem
  [    0.000000][    T0] Kernel parameter elevator= does not have any
effect anymore.
  [    0.000000][    T0] Please use sysfs to set IO scheduler for
individual devices.
  [    0.000000][    T0] printk: log buffer data + meta data: 131072 +
458752 = 589824 bytes
  ...

...current atmel-sha204a:
root@dut02:~/atsha204a-orig# insmod atmel-i2c.ko
root@dut02:~/atsha204a-orig# insmod atmel-sha204a.ko
root@dut02:~/atsha204a-orig# cat /sys/bus/i2c/devices/1-0064/atsha204a/otp
0001ED86032D0002154C033750FFFFFF20B0F703DB0CFFFFFFFFFFFFFFFFFFFF

reboot...

...atmel-sha204a with patch applied:
root@dut02:~/atsha204a# modprobe i2c-dev
root@dut02:~/atsha204a# insmod ./atmel-i2c.ko
root@dut02:~/atsha204a# insmod ./atmel-sha204a.ko
root@dut02:~/atsha204a# cat /sys/bus/i2c/devices/1-0064/atsha204a/otp
0root@dut02:~/atsha204a#
root@dut02:~/atsha204a# xxd /sys/bus/i2c/devices/1-0064/atsha204a/otp
00000000: 30                                       0
8<-------------------------------------------------------------->8

Best,
L

On Sun, Feb 15, 2026 at 1:42 PM Thorsten Blum <thorsten.blum@xxxxxxxxx> wrote:
>
> Fix otp_show() to read and print all 64 bytes of the OTP zone.
> Previously, the loop only printed half of the OTP (32 bytes), and
> partial output was returned on read errors.
>
> Propagate the actual error from atmel_sha204a_otp_read() instead of
> producing partial output.
>
> Replace sprintf() with sysfs_emit_at(), which is preferred for
> formatting sysfs output because it provides safer bounds checking.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 13909a0c8897 ("crypto: atmel-sha204a - provide the otp content")
> Signed-off-by: Thorsten Blum <thorsten.blum@xxxxxxxxx>
> ---
> Compile-tested only.
> ---
>  drivers/crypto/atmel-sha204a.c | 19 ++++++++++---------
>  1 file changed, 10 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/crypto/atmel-sha204a.c b/drivers/crypto/atmel-sha204a.c
> index 0fcf4a39de27..793c8d739a0a 100644
> --- a/drivers/crypto/atmel-sha204a.c
> +++ b/drivers/crypto/atmel-sha204a.c
> @@ -15,6 +15,7 @@
>  #include <linux/module.h>
>  #include <linux/scatterlist.h>
>  #include <linux/slab.h>
> +#include <linux/sysfs.h>
>  #include <linux/workqueue.h>
>  #include "atmel-i2c.h"
>
> @@ -119,21 +120,21 @@ static ssize_t otp_show(struct device *dev,
>  {
>         u16 addr;
>         u8 otp[OTP_ZONE_SIZE];
> -       char *str = buf;
>         struct i2c_client *client = to_i2c_client(dev);
> -       int i;
> +       ssize_t len = 0;
> +       int i, ret;
>
> -       for (addr = 0; addr < OTP_ZONE_SIZE/4; addr++) {
> -               if (atmel_sha204a_otp_read(client, addr, otp + addr * 4) < 0) {
> +       for (addr = 0; addr < OTP_ZONE_SIZE / 4; addr++) {
> +               ret = atmel_sha204a_otp_read(client, addr, otp + addr * 4);
> +               if (ret < 0) {
>                         dev_err(dev, "failed to read otp zone\n");
> -                       break;
> +                       return ret;
>                 }
>         }
>
> -       for (i = 0; i < addr*2; i++)
> -               str += sprintf(str, "%02X", otp[i]);
> -       str += sprintf(str, "\n");
> -       return str - buf;
> +       for (i = 0; i < OTP_ZONE_SIZE; i++)
> +               len += sysfs_emit_at(buf, len, "%02X", otp[i]);
> +       return sysfs_emit_at(buf, len, "\n");
>  }
>  static DEVICE_ATTR_RO(otp);
>
> --
> Thorsten Blum <thorsten.blum@xxxxxxxxx>
> GPG: 1D60 735E 8AEF 3BE4 73B6  9D84 7336 78FD 8DFE EAD4
>