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

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Message-ID: <87r001uliz.fsf@posteo.net>
Date: Tue, 03 Jun 2025 11:12:04 +0000
From: Charalampos Mitrodimas <charmitro@...teo.net>
To: Bastien Nocera <hadess@...ess.net>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,  Alan Stern
 <stern@...land.harvard.edu>,  linux-usb@...r.kernel.org,
  linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: misc: apple-mfi-fastcharge: Make power supply
 names unique

Bastien Nocera <hadess@...ess.net> writes:

> 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

Hi Bastien,

Thanks for the review!

FWIW, this has been tested in QEMU via,

      -device usb-host,bus=ehci.0,vendorid=0x05ac,productid=0x12a8
      -device usb-host,bus=ehci.0,vendorid=0x05ac,productid=0x12ab

And works as expected,

$ ls /sys/class/power_supply
apple_mfi_fastcharge_2_2  apple_mfi_fastcharge_2_3

C. Mitrodimas

>
> 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,