linux-kernel - Re: [PATCH v12 3/4] PCI/DOE: Expose the DOE features via sysfs

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Date: Mon, 1 Jul 2024 12:27:21 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Alistair Francis <alistair23@...il.com>
CC: <bhelgaas@...gle.com>, <linux-pci@...r.kernel.org>, <lukas@...ner.de>,
	<alex.williamson@...hat.com>, <christian.koenig@....com>, <kch@...dia.com>,
	<gregkh@...uxfoundation.org>, <logang@...tatee.com>,
	<linux-kernel@...r.kernel.org>, <chaitanyak@...dia.com>,
	<rdunlap@...radead.org>, Alistair Francis <alistair.francis@....com>
Subject: Re: [PATCH v12 3/4] PCI/DOE: Expose the DOE features via sysfs

On Wed, 26 Jun 2024 14:59:25 +1000
Alistair Francis <alistair23@...il.com> wrote:

> The PCIe 6 specification added support for the Data Object
> Exchange (DOE).
> When DOE is supported the DOE Discovery Feature must be implemented per
> PCIe r6.1 sec 6.30.1.1. The protocol allows a requester to obtain
> information about the other DOE features supported by the device.
> 
> The kernel is already querying the DOE features supported and cacheing
> the values. Expose the values in sysfs to allow user space to
> determine which DOE features are supported by the PCIe device.
> 
> By exposing the information to userspace tools like lspci can relay the
> information to users. By listing all of the supported features we can
> allow userspace to parse the list, which might include
> vendor specific features as well as yet to be supported features.
> 
> As the DOE Discovery feature must always be supported we treat it as a
> special named attribute case. This allows the usual PCI attribute_group
> handling to correctly create the doe_features directory when registering
> pci_doe_sysfs_group (otherwise it doesn't and sysfs_add_file_to_group()
> will seg fault).
> 
> After this patch is supported you can see something like this when
> attaching a DOE device
> 
> $ ls /sys/devices/pci0000:00/0000:00:02.0//doe*
> 0001:01        0001:02        doe_discovery
> 
> Signed-off-by: Alistair Francis <alistair.francis@....com>
Hi Alistair,

I think I missed an error path issue in earlier reviews.

Suggestion for minimal fix inline. If that is fine feel
free to add

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>

> diff --git a/drivers/pci/doe.c b/drivers/pci/doe.c
> index defc4be81bd4..580370dc71ee 100644
> --- a/drivers/pci/doe.c
> +++ b/drivers/pci/doe.c


> +
> +int pci_doe_sysfs_init(struct pci_dev *pdev)
> +{
> +	struct pci_doe_mb *doe_mb;
> +	unsigned long index;
> +	int ret;
> +
> +	xa_for_each(&pdev->doe_mbs, index, doe_mb) {
> +		ret = pci_doe_sysfs_feature_populate(pdev, doe_mb);

This doesn't feel quite right.  If we wait after a doe_mb features
set succeeds and then an error occurs this code doesn't cleanup and...

> +		if (ret)
> +			return ret;
> +	}
> +
> +	return 0;
> +}
> +#endif
> +
>  static int pci_doe_wait(struct pci_doe_mb *doe_mb, unsigned long timeout)
>  {
>  	if (wait_event_timeout(doe_mb->wq,
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 40cfa716392f..b5db191cb29f 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -16,6 +16,7 @@
>  #include <linux/kernel.h>
>  #include <linux/sched.h>
>  #include <linux/pci.h>
> +#include <linux/pci-doe.h>
>  #include <linux/stat.h>
>  #include <linux/export.h>
>  #include <linux/topology.h>
> @@ -1143,6 +1144,9 @@ static void pci_remove_resource_files(struct pci_dev *pdev)
>  {
>  	int i;
>  
> +	if (IS_ENABLED(CONFIG_PCI_DOE))
> +		pci_doe_sysfs_teardown(pdev);
> +
>  	for (i = 0; i < PCI_STD_NUM_BARS; i++) {
>  		struct bin_attribute *res_attr;
>  
> @@ -1227,6 +1231,12 @@ static int pci_create_resource_files(struct pci_dev *pdev)
>  	int i;
>  	int retval;
>  
> +	if (IS_ENABLED(CONFIG_PCI_DOE)) {
> +		retval = pci_doe_sysfs_init(pdev);
> +		if (retval)

... this doesn't call pci_remove_resource_files() unlike te
other error path in this function which does.

I think just calling that here would be sufficient and inline
with how error cleanup works for the rest of this code.
Personally I prefer driving for a function to have no side effects
but such is life.

> +			return retval;
> +	}
> +
>  	/* Expose the PCI resources from this device as files */
>  	for (i = 0; i < PCI_STD_NUM_BARS; i++) {
>  
> @@ -1661,6 +1671,9 @@ const struct attribute_group *pci_dev_attr_groups[] = {
>  #endif
>  #ifdef CONFIG_PCIEASPM
>  	&aspm_ctrl_attr_group,
> +#endif
> +#ifdef CONFIG_PCI_DOE
> +	&pci_doe_sysfs_group,
>  #endif
>  	NULL,
>  };