linux-kernel - Re: [PATCH] usb: misc: apple-mfi-fastcharge: Make power supply names unique

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Message-ID: <5a610d364c8a8148e48d5bf7a95e73fc81650e5a.camel@hadess.net>
Date: Mon, 02 Jun 2025 20:48:00 +0200
From: Bastien Nocera <hadess@...ess.net>
To: Charalampos Mitrodimas <charmitro@...teo.net>, Greg Kroah-Hartman
	 <gregkh@...uxfoundation.org>, Alan Stern <stern@...land.harvard.edu>
Cc: linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: misc: apple-mfi-fastcharge: Make power supply
 names unique

On Mon, 2025-06-02 at 18:26 +0000, Charalampos Mitrodimas wrote:
> When multiple Apple devices are connected concurrently, the
> apple-mfi-fastcharge driver fails to probe the subsequent devices
> with
> the following error:
> 
>     sysfs: cannot create duplicate filename
> '/class/power_supply/apple_mfi_fastcharge'
>     apple-mfi-fastcharge 5-2.4.3.3: probe of 5-2.4.3.3 failed with
> error -17
> 
> This happens because the driver uses a fixed power supply name
> ("apple_mfi_fastcharge") for all devices, causing a sysfs name
> conflict when a second device is connected.
> 
> Fix this by generating unique names using the USB bus and device
> number (e.g., "apple_mfi_fastcharge_5-12"). This ensures each
> connected device gets a unique power supply entry in sysfs.
> 
> The change requires storing a copy of the power_supply_desc structure
> in the per-device mfi_device struct, since the name pointer needs to
> remain valid for the lifetime of the power supply registration.
> 
> Fixes: 249fa8217b84 ("USB: Add driver to control USB fast charge for
> iOS devices")
> Signed-off-by: Charalampos Mitrodimas <charmitro@...teo.net>
> ---
>  drivers/usb/misc/apple-mfi-fastcharge.c | 24 +++++++++++++++++++++--
> -
>  1 file changed, 21 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/usb/misc/apple-mfi-fastcharge.c
> b/drivers/usb/misc/apple-mfi-fastcharge.c
> index
> ac8695195c13c8752076e4391ac81a9da3780c44..8e852f4b8262e6e8fcd33883be8
> c5696f19b9ee9 100644
> --- a/drivers/usb/misc/apple-mfi-fastcharge.c
> +++ b/drivers/usb/misc/apple-mfi-fastcharge.c
> @@ -44,6 +44,7 @@ MODULE_DEVICE_TABLE(usb, mfi_fc_id_table);
>  struct mfi_device {
>  	struct usb_device *udev;
>  	struct power_supply *battery;
> +	struct power_supply_desc battery_desc;
>  	int charge_type;
>  };
>  
> @@ -178,6 +179,7 @@ static int mfi_fc_probe(struct usb_device *udev)
>  {
>  	struct power_supply_config battery_cfg = {};
>  	struct mfi_device *mfi = NULL;
> +	char *battery_name;
>  	int err;
>  
>  	if (!mfi_fc_match(udev))
> @@ -187,23 +189,38 @@ static int mfi_fc_probe(struct usb_device
> *udev)
>  	if (!mfi)
>  		return -ENOMEM;
>  
> +	battery_name = kasprintf(GFP_KERNEL,
> "apple_mfi_fastcharge_%d-%d",
> +				 udev->bus->busnum, udev->devnum);

Looks fine to me although I don't know how common this construct is.

If others think this won't work, you can use the ever increasing id as
used in drivers/hid/hid-steelseries.c

Cheers

> +	if (!battery_name) {
> +		err = -ENOMEM;
> +		goto err_free_mfi;
> +	}
> +
> +	mfi->battery_desc = apple_mfi_fc_desc;
> +	mfi->battery_desc.name = battery_name;
> +
>  	battery_cfg.drv_data = mfi;
>  
>  	mfi->charge_type = POWER_SUPPLY_CHARGE_TYPE_TRICKLE;
>  	mfi->battery = power_supply_register(&udev->dev,
> -						&apple_mfi_fc_desc,
> +						&mfi->battery_desc,
>  						&battery_cfg);
>  	if (IS_ERR(mfi->battery)) {
>  		dev_err(&udev->dev, "Can't register battery\n");
>  		err = PTR_ERR(mfi->battery);
> -		kfree(mfi);
> -		return err;
> +		goto err_free_name;
>  	}
>  
>  	mfi->udev = usb_get_dev(udev);
>  	dev_set_drvdata(&udev->dev, mfi);
>  
>  	return 0;
> +
> +err_free_name:
> +	kfree(battery_name);
> +err_free_mfi:
> +	kfree(mfi);
> +	return err;
>  }
>  
>  static void mfi_fc_disconnect(struct usb_device *udev)
> @@ -213,6 +230,7 @@ static void mfi_fc_disconnect(struct usb_device
> *udev)
>  	mfi = dev_get_drvdata(&udev->dev);
>  	if (mfi->battery)
>  		power_supply_unregister(mfi->battery);
> +	kfree(mfi->battery_desc.name);
>  	dev_set_drvdata(&udev->dev, NULL);
>  	usb_put_dev(mfi->udev);
>  	kfree(mfi);
> 
> ---
> base-commit: cd2e103d57e5615f9bb027d772f93b9efd567224
> change-id: 20250602-apple-mfi-fastcharge-duplicate-sysfs-0ef3864b21f8
> 
> Best regards,