Re: [PATCH v1] can: peak_usb: export PCAN device ID as sysfs device attribute

[Vincent MAILHOL <mailhol.vincent@wanadoo.fr>]

Hi Lukas,

Welcome on the linux-can mailing list!

On Mon. 1 août 2022 at 17:13, Lukas Magel <lukas.magel@posteo.net> wrote:
> Peak USB devices support a configurable u8 / u32 device ID. In
> multi-device setups, this device ID can be configured and used to
> identify individual CAN interfaces independent of the order in which
> they are plugged into the system. At the current time, the device ID
> is already queried from the device and stored in the peak_usb_device
> struct.
>
> This patch exports the device ID (called device_number in the struct)
> as a sysfs attribute. The attribute name was chosen to be device_id
> instead of device_number because the latter has been deprecated by Peak
> in their API.
>
> Signed-off-by: Lukas Magel <lukas.magel@posteo.net>
> Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>

For the public record, I did the review in private message.

> ---
> For the moment, the patch only implements read support for the device
> ID. My next goal is to also implement write access. However, this
> will require a more significant modification of the driver since the
> corresponding commands for ID retrieval and configuration are not
> implemented for all device types.
>
>  drivers/net/can/usb/peak_usb/pcan_usb_core.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
>
> diff --git a/drivers/net/can/usb/peak_usb/pcan_usb_core.c b/drivers/net/can/usb/peak_usb/pcan_usb_core.c
> index 27b0a72fd885..43df178e9473 100644
> --- a/drivers/net/can/usb/peak_usb/pcan_usb_core.c
> +++ b/drivers/net/can/usb/peak_usb/pcan_usb_core.c
> @@ -15,6 +15,8 @@
>  #include <linux/netdevice.h>
>  #include <linux/usb.h>
>  #include <linux/ethtool.h>
> +#include <linux/device.h>
> +#include <linux/sysfs.h>
>
>  #include <linux/can.h>
>  #include <linux/can/dev.h>
> @@ -53,6 +55,15 @@ static const struct usb_device_id peak_usb_table[] = {
>
>  MODULE_DEVICE_TABLE(usb, peak_usb_table);
>
> +static ssize_t device_id_show(struct device *dev, struct device_attribute *attr, char *buf)
> +{
> +       struct net_device *netdev = to_net_dev(dev);
> +       struct peak_usb_device *peak_dev = netdev_priv(netdev);
> +
> +       return sysfs_emit(buf, "%08X\n", peak_dev->device_number);
> +}
> +static DEVICE_ATTR_RO(device_id);
> +
>  /*
>   * dump memory
>   */
> @@ -887,6 +898,11 @@ static int peak_usb_create_dev(const struct peak_usb_adapter *peak_usb_adapter,
>         netdev_info(netdev, "attached to %s channel %u (device %u)\n",
>                         peak_usb_adapter->name, ctrl_idx, dev->device_number);
>
> +       err = device_create_file(&netdev->dev, &dev_attr_device_id);
> +       /* Do not error out since device was configured successfully */
> +       if (err)
> +               netdev_warn(netdev, "unable to expose device_id via sysfs %d\n", err);

netdev_warn(netdev, "unable to expose device_id via sysfs %pe\n", ERR_PTR(err));

I forgot this point in my first review. The %pe will print the
mnemotechnic instead of the error number. c.f.:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=57f5677e535ba24b8926a7125be2ef8d7f09323c

> +
>         return 0;
>
>  adap_dev_free:
> @@ -923,6 +939,8 @@ static void peak_usb_disconnect(struct usb_interface *intf)
>                 dev->state &= ~PCAN_USB_STATE_CONNECTED;
>                 strlcpy(name, netdev->name, IFNAMSIZ);
>
> +               device_remove_file(&netdev->dev, &dev_attr_device_id);
> +
>                 unregister_netdev(netdev);
>
>                 kfree(dev->cmd_buf);
> --
> 2.37.1
>