Re: [PATCH v5 1/1] PCI/sysfs: Expose PCIe device serial number

[Jonathan Cameron <Jonathan.Cameron@huawei.com>]

On Fri, 18 Jul 2025 13:02:00 +0200
Thomas Weißschuh <thomas.weissschuh@linutronix.de> wrote:

> On Fri, Jul 18, 2025 at 11:36:11AM +0100, Jonathan Cameron wrote:
> > On Thu, 17 Jul 2025 09:50:54 -0700
> > Matthew Wood <thepacketgeek@gmail.com> wrote:  
> 
> (...)
> 
> > > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> > > index 268c69daa4d5..bc0e0add15d1 100644
> > > --- a/drivers/pci/pci-sysfs.c
> > > +++ b/drivers/pci/pci-sysfs.c
> > > @@ -239,6 +239,22 @@ static ssize_t current_link_width_show(struct device *dev,
> > >  }
> > >  static DEVICE_ATTR_RO(current_link_width);
> > >  
> > > +static ssize_t serial_number_show(struct device *dev,
> > > +				       struct device_attribute *attr, char *buf)
> > > +{
> > > +	struct pci_dev *pci_dev = to_pci_dev(dev);
> > > +	u64 dsn;
> > > +
> > > +	dsn = pci_get_dsn(pci_dev);
> > > +	if (!dsn)
> > > +		return -EIO;
> > > +
> > > +	return sysfs_emit(buf, "%02llx-%02llx-%02llx-%02llx-%02llx-%02llx-%02llx-%02llx\n",
> > > +		dsn >> 56, (dsn >> 48) & 0xff, (dsn >> 40) & 0xff, (dsn >> 32) & 0xff,
> > > +		(dsn >> 24) & 0xff, (dsn >> 16) & 0xff, (dsn >> 8) & 0xff, dsn & 0xff);  
> > 
> > I wonder if doing the following i too esoteric. Eyeballing those shifts is painful.
> > 
> > 	u8 bytewise[8]; /* naming hard... */
> > 
> > 	put_unaligned_u64(dsn, bytewise);
> > 
> > 	return sysfs_emit(buf, "%02x-%02x-%02x-%02x-%02x-%02x-%02x-%02x\n",
> > 		bytewise[0], bytewise[1], bytewise[2], bytewise[3],
> > 		bytewise[4], bytewise[5], bytewise[6], bytewise[7]);  
> 
> This looks endianess-unsafe.
> 
> Maybe just do what some drivers are doing:
> 
> 	u8 bytes[8];
> 
> 	put_unaligned_be64(dsn, bytes);
Absolutely. Typo :(  I don't think there is a put_unaligned_u64()

> 
> 	return sysfs_emit(buf, "%8phD");
> 
> > 
> >   
> > > +}
> > > +static DEVICE_ATTR_ADMIN_RO(serial_number);  
> > 
> >   
>