linux-kernel - Re: [PATCH] PCI: s390: Expose the UID as an arch specific PCI slot attribute

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Message-ID: <20250926142714.GB17059@p1gen4-pw042f0m.boeblingen.de.ibm.com>
Date: Fri, 26 Sep 2025 16:27:14 +0200
From: Benjamin Block <bblock@...ux.ibm.com>
To: Niklas Schnelle <schnelle@...ux.ibm.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, Lukas Wunner <lukas@...ner.de>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Gerd Bayer <gbayer@...ux.ibm.com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Julian Ruess <julianr@...ux.ibm.com>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>,
        Ramesh Errabolu <ramesh@...ux.ibm.com>, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH] PCI: s390: Expose the UID as an arch specific PCI slot
 attribute

> diff --git a/arch/s390/include/asm/pci.h b/arch/s390/include/asm/pci.h
> index 41f900f693d92522ff729829e446b581977ef3ff..23eed78d9dce72ef466679f31c78aca52ba00f99 100644
> --- a/arch/s390/include/asm/pci.h
> +++ b/arch/s390/include/asm/pci.h
> @@ -207,6 +207,10 @@ extern const struct attribute_group zpci_ident_attr_group;
>  			    &pfip_attr_group,		 \
>  			    &zpci_ident_attr_group,
>  
> +extern const struct attribute_group zpci_slot_attr_group;
> +
> +#define ARCH_PCI_SLOT_GROUPS (&zpci_slot_attr_group)

I don't know the history exactly, but this can't be easily extended like the
other group above `ARCH_PCI_DEV_GROUPS`.

    (&zpci_slot_attr_group,  \
     &zpci_slot_attr_group_b)

Won't compile. The way `ARCH_PCI_DEV_GROUPS` does it, attaching a different
group is just adding a new line.

> diff --git a/arch/s390/pci/pci_sysfs.c b/arch/s390/pci/pci_sysfs.c
> index 0ee0924cfab7e5d22468fb197ee78cac679d8c13..997dff3796094680d9a3f0b6eb27a89fa1ed30b2 100644
> --- a/arch/s390/pci/pci_sysfs.c
> +++ b/arch/s390/pci/pci_sysfs.c
> @@ -178,6 +178,17 @@ static ssize_t index_show(struct device *dev,
>  }
>  static DEVICE_ATTR_RO(index);
>  
> +static ssize_t zpci_uid_slot_show(struct pci_slot *slot, char *buf)
> +{
> +	struct zpci_dev *zdev = container_of(slot->hotplug, struct zpci_dev,
> +					     hotplug_slot);
> +
> +	return sysfs_emit(buf, "0x%x\n", zdev->uid);

Do we need a special case for when `uid` is 0? That would imply the uid is
invalid, right? Would we want to return an error in that case (-EINVAL, or
smth)? 

Also, do we want to use the same format as in `zpci_setup_bus_resources()`
with the 4 leading 0's (`0x%04x`)?

> +}
> +
> +static struct pci_slot_attribute zpci_slot_attr_uid =
> +	__ATTR(uid, 0444, zpci_uid_slot_show, NULL);

__ATTR_RO()?

-- 
Best Regards, Benjamin Block        /        Linux on IBM Z Kernel Development
IBM Deutschland Research & Development GmbH    /   https://www.ibm.com/privacy
Vors. Aufs.-R.: Wolfgang Wendt         /        Geschäftsführung: David Faller
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