Re: [PATCH v1 1/1] HID: nintendo: Use %pM format specifier for MAC addresses

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Wed, Jun 03, 2026 at 08:39:46AM +0000, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Critical] ABI Breakage: The patch changes the MAC address exposed via sysfs from uppercase to lowercase, breaking userspace tools that rely on exact string matching.
> --
> 
> commit 6c8c4e53eb547a4381d6f8dabe9201540c4f0168
> Author: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> 
> HID: nintendo: Use %pM format specifier for MAC addresses
> 
> This commit refactors the MAC address string generation in the nintendo HID
> driver. It replaces a custom sprintf format string with the standard %pM
> format specifier.
> 
> > diff --git a/drivers/hid/hid-nintendo.c b/drivers/hid/hid-nintendo.c
> > index 29008c2cc5304..77b14dfdae867 100644
> > --- a/drivers/hid/hid-nintendo.c
> > +++ b/drivers/hid/hid-nintendo.c
> > @@ -2431,14 +2431,8 @@ static int joycon_read_info(struct joycon_ctlr *ctlr)
> >  	for (i = 4, j = 0; j < 6; i++, j++)
> >  		ctlr->mac_addr[j] = report->subcmd_reply.data[i];
> >  
> > -	ctlr->mac_addr_str = devm_kasprintf(&ctlr->hdev->dev, GFP_KERNEL,
> > -					    "%02X:%02X:%02X:%02X:%02X:%02X",
> > -					    ctlr->mac_addr[0],
> > -					    ctlr->mac_addr[1],
> > -					    ctlr->mac_addr[2],
> > -					    ctlr->mac_addr[3],
> > -					    ctlr->mac_addr[4],
> > -					    ctlr->mac_addr[5]);
> > +	ctlr->mac_addr_str = devm_kasprintf(&ctlr->hdev->dev, GFP_KERNEL, "%pM",
> > +					    ctlr->mac_addr);
> 
> [Severity: Critical]
> Does this change the sysfs output from uppercase to lowercase?

I think yes, it does.

> The original format string %02X explicitly generated an uppercase MAC
> address string, while %pM delegates to hex_byte_pack() and generates a
> lowercase string.
> 
> Since ctlr->mac_addr_str is exposed to userspace via the uniq attribute,
> could this cause an ABI regression?

This is a good question. This is MAC address string and conceptually the
user space should be prepared to parse it as a mac address and not an arbitrary
string. OTOH, the field is named something like uniq, which means the
driver just supplies MAC as an arbitrary (unique) string.

> Userspace utilities and gaming libraries (like SDL and the joycond daemon)
> often map USB controllers to their Bluetooth pairings by performing
> case-sensitive matching against the uppercase Bluetooth MAC addresses
> exposed by BlueZ.

Hmm... Interesting. Okay, perhaps we need to have %pMU first.

-- 
With Best Regards,
Andy Shevchenko