linux-kernel - Re: [PATCH v9 2/3] PCI/DOE: Expose the DOE features via sysfs

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Message-ID: <20231017083421.GA23168@wunner.de>
Date:   Tue, 17 Oct 2023 10:34:21 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     Alistair Francis <alistair23@...il.com>
Cc:     bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        Jonathan.Cameron@...wei.com, 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 v9 2/3] PCI/DOE: Expose the DOE features via sysfs

On Fri, Oct 13, 2023 at 01:41:57PM +1000, Alistair Francis wrote:
> +#ifdef CONFIG_SYSFS
> +static umode_t pci_doe_sysfs_attr_is_visible(struct kobject *kobj,
> +					     struct attribute *a, int n)
> +{
> +	struct pci_dev *pdev = to_pci_dev(kobj_to_dev(kobj));
> +	struct pci_doe_mb *doe_mb;
> +	unsigned long index, j;
> +	void *entry;
> +
> +	xa_for_each(&pdev->doe_mbs, index, doe_mb) {
> +		xa_for_each(&doe_mb->feats, j, entry)
> +			return a->mode;
> +	}
> +
> +	return 0;
> +}

Out of curiosity:  Does this method prevent creation of a
"doe_features" directory for devices which don't have any
DOE mailboxes?

(If it does, a code comment explaining that might be helpful.)


> +const struct attribute_group pci_dev_doe_feature_group = {
> +	.name	= "doe_features",
> +	.attrs	= pci_dev_doe_feature_attrs,
> +	.is_visible = pci_doe_sysfs_attr_is_visible,
> +};

Nit:  Wondering why the "=" is aligned for .name and .attrs
but not for .is_visible?


> +static void pci_doe_sysfs_feature_remove(struct pci_dev *pdev,
> +					 struct pci_doe_mb *doe_mb)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct device_attribute *attrs = doe_mb->sysfs_attrs;
> +	unsigned long i;
> +	void *entry;

Nit:  Inverse Christmas tree?


> +static int pci_doe_sysfs_feature_populate(struct pci_dev *pdev,
> +					  struct pci_doe_mb *doe_mb)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct device_attribute *attrs;
> +	unsigned long num_features = 0;
> +	unsigned long vid, type;
> +	unsigned long i;
> +	void *entry;
> +	int ret;
> +
> +	xa_for_each(&doe_mb->feats, i, entry)
> +		num_features++;
> +
> +	attrs = kcalloc(num_features, sizeof(*attrs), GFP_KERNEL);
> +	if (!attrs)
> +		return -ENOMEM;
> +
> +	doe_mb->sysfs_attrs = attrs;
> +	xa_for_each(&doe_mb->feats, i, entry) {
> +		sysfs_attr_init(&attrs[i].attr);
> +		vid = xa_to_value(entry) >> 8;
> +		type = xa_to_value(entry) & 0xFF;
> +		attrs[i].attr.name = kasprintf(GFP_KERNEL,
> +					       "0x%04lX:%02lX", vid, type);

Nit:  Capital X conversion specifier will result in upper case hex
characters in filename and contents, whereas existing sysfs attributes
such as "vendor", "device" contain lower case hex characters.

Might want to consider lower case x for consistency.


> +void pci_doe_sysfs_teardown(struct pci_dev *pdev)
> +{
> +	struct pci_doe_mb *doe_mb;
> +	unsigned long index;
> +
> +	xa_for_each(&pdev->doe_mbs, index, doe_mb) {
> +		pci_doe_sysfs_feature_remove(pdev, doe_mb);
> +	}

Nit:  Curly braces not necessary.


> @@ -1153,6 +1154,10 @@ static void pci_remove_resource_files(struct pci_dev *pdev)
>  {
>  	int i;
>  
> +	if (IS_ENABLED(CONFIG_PCI_DOE)) {
> +		pci_doe_sysfs_teardown(pdev);
> +	}

Nit:  Curly braces not necessary.


> @@ -1230,6 +1235,12 @@ 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)
> +			return retval;
> +	}
> +
>  	/* Expose the PCI resources from this device as files */
>  	for (i = 0; i < PCI_STD_NUM_BARS; i++) {

I think this needs to be added to pci_create_sysfs_dev_files() instead.

pci_create_resource_files() only deals with creation of resource files,
as the name implies, which is unrelated to DOE features.

Worse, pci_create_resource_files() is also called from
pci_dev_resource_resize_attr(), i.e. every time user space
writes to the "resource##n##_resize" attributes.

Similarly, the call to pci_doe_sysfs_teardown() belongs in
pci_remove_sysfs_dev_files().

Thanks,

Lukas