Re: [PATCH v3 1/3] PCI: Make specifying PCI devices in kernel parameters reusable

[Alex Williamson]

On Mon, 18 Jun 2018 13:36:34 -0600
Logan Gunthorpe <logang@xxxxxxxxxxxx> wrote:

> Separate out the code to match a PCI device with a string (typically
> originating from a kernel parameter) from the
> pci_specified_resource_alignment() function into its own helper
> function.
> 
> While we are at it, this change fixes the kernel style of the function
> (fixing a number of long lines and extra parentheses).
> 
> Additionally, make the analogous change to the kernel parameter
> documentation: Separating the description of how to specify a PCI device
> into it's own section at the head of the pci= parameter.
> 
> This patch should have no functional alterations.
> 
> Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
> Reviewed-by: Stephen Bates <sbates@xxxxxxxxxxxx>
> Acked-by: Christian KÃnig <christian.koenig@xxxxxxx>
> ---
>  Documentation/admin-guide/kernel-parameters.txt |  26 +++-
>  drivers/pci/pci.c                               | 153 +++++++++++++++---------
>  2 files changed, 120 insertions(+), 59 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index efc7aa7a0670..760fb2b0b349 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2994,7 +2994,24 @@
>  			See header of drivers/block/paride/pcd.c.
>  			See also Documentation/blockdev/paride.txt.
>  
> -	pci=option[,option...]	[PCI] various PCI subsystem options:
> +	pci=option[,option...]	[PCI] various PCI subsystem options.
> +
> +				Some options herein operate on a specific device
> +				or a set of devices (<pci_dev>). These are
> +				specified in one of the following formats:
> +
> +				[<domain>:]<bus>:<slot>.<func>
> +				pci:<vendor>:<device>[:<subvendor>:<subdevice>]
> +
> +				Note: the first format specifies a PCI
> +				bus/slot/function address which may change
> +				if new hardware is inserted, if motherboard
> +				firmware changes, or due to changes caused
> +				by other kernel parameters. The second format

Nit, is it worth noting that when unspecified, domain is zero?

> +				selects devices using IDs from the
> +				configuration space which may match multiple
> +				devices in the system.
> +
>  		earlydump	[X86] dump PCI config space before the kernel
>  				changes anything
>  		off		[X86] don't probe for the PCI bus
> @@ -3123,11 +3140,10 @@
>  				window. The default value is 64 megabytes.
>  		resource_alignment=
>  				Format:
> -				[<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
> -				[<order of align>@]pci:<vendor>:<device>\
> -						[:<subvendor>:<subdevice>][; ...]
> +				[<order of align>@]<pci_dev>[; ...]
>  				Specifies alignment and device to reassign
> -				aligned memory resources.
> +				aligned memory resources. How to
> +				specify the device is described above.
>  				If <order of align> is not specified,
>  				PAGE_SIZE is used as alignment.
>  				PCI-PCI bridge can be specified, if resource
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 97acba712e4e..bec1bef6f326 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -191,6 +191,88 @@ void __iomem *pci_ioremap_wc_bar(struct pci_dev *pdev, int bar)
>  EXPORT_SYMBOL_GPL(pci_ioremap_wc_bar);
>  #endif
>  
> +/**
> + * pci_dev_str_match - test if a string matches a device
> + * @dev:    the PCI device to test
> + * @p:      string to match the device against
> + * @endptr: pointer to the string after the match
> + *
> + * Test if a string (typically from a kernel parameter) matches a
> + * specified. The string may be of one of two forms formats:
> + *
> + *   [<domain>:]<bus>:<slot>.<func>
> + *   pci:<vendor>:<device>[:<subvendor>:<subdevice>]
> + *
> + * The first format specifies a PCI bus/slot/function address which
> + * may change if new hardware is inserted, if motherboard firmware changes,
> + * or due to changes caused in kernel parameters.
> + *
> + * The second format matches devices using IDs in the configuration
> + * space which may match multiple devices in the system. A value of 0
> + * for any field will match all devices.

I realize this is not a change in behavior, but since we're spelling it
out in a proper comment rather than burying it in the implementation,
using 0 as a wildcard is rather questionable behavior.  It always
surprises me when I read this because pci_match_one_device() uses
PCI_ANY_ID (~0) as a wildcard and as a result of struct pci_device_id
using __u32 for these fields, we actually need to specify ffffffff on
the commandline to get a wildcard match for dynamic ids.  The latter is
tedious to use, but I think it's more correct, and the use of a __u32 is
probably attributed to the fact that 0xffff is only reserved for vendor
ID, the spec doesn't seem to reserve any entries from the vendor's
device ID range.

There's probably really no path to resolve these, but acknowledging the
difference in this comment block might be helpful in the future.

> + *
> + * Returns 1 if the string matches the device, 0 if it does not and
> + * a negative error code if the string cannot be parsed.
> + */
> +static int pci_dev_str_match(struct pci_dev *dev, const char *p,
> +			     const char **endptr)
> +{
> +	int ret;
> +	int seg, bus, slot, func, count;
> +	unsigned short vendor, device, subsystem_vendor, subsystem_device;
> +
> +	if (strncmp(p, "pci:", 4) == 0) {
> +		/* PCI vendor/device (subvendor/subdevice) ids are specified */
> +		p += 4;
> +		ret = sscanf(p, "%hx:%hx:%hx:%hx%n", &vendor, &device,
> +			     &subsystem_vendor, &subsystem_device, &count);
> +		if (ret != 4) {
> +			ret = sscanf(p, "%hx:%hx%n", &vendor, &device, &count);
> +			if (ret != 2)
> +				return -EINVAL;
> +
> +			subsystem_vendor = 0;
> +			subsystem_device = 0;
> +		}
> +
> +		p += count;
> +
> +		if ((!vendor || vendor == dev->vendor) &&
> +		    (!device || device == dev->device) &&
> +		    (!subsystem_vendor ||
> +			    subsystem_vendor == dev->subsystem_vendor) &&
> +		    (!subsystem_device ||
> +			    subsystem_device == dev->subsystem_device))
> +			goto found;
> +
> +	} else {
> +		/* PCI Bus,Slot,Function ids are specified */
> +		ret = sscanf(p, "%x:%x:%x.%x%n", &seg, &bus, &slot,
> +			     &func, &count);
> +		if (ret != 4) {
> +			seg = 0;
> +			ret = sscanf(p, "%x:%x.%x%n", &bus, &slot,
> +				     &func, &count);
> +			if (ret != 3)
> +				return -EINVAL;
> +		}
> +
> +		p += count;
> +
> +		if (seg == pci_domain_nr(dev->bus) &&
> +		    bus == dev->bus->number &&
> +		    slot == PCI_SLOT(dev->devfn) &&
> +		    func == PCI_FUNC(dev->devfn))
> +			goto found;
> +	}
> +
> +	*endptr = p;
> +	return 0;
> +
> +found:
> +	*endptr = p;
> +	return 1;
> +}
>  
>  static int __pci_find_next_cap_ttl(struct pci_bus *bus, unsigned int devfn,
>  				   u8 pos, int cap, int *ttl)
> @@ -5454,10 +5536,10 @@ static DEFINE_SPINLOCK(resource_alignment_lock);
>  static resource_size_t pci_specified_resource_alignment(struct pci_dev *dev,
>  							bool *resize)
>  {
> -	int seg, bus, slot, func, align_order, count;
> -	unsigned short vendor, device, subsystem_vendor, subsystem_device;
> +	int align_order, count;
>  	resource_size_t align = pcibios_default_alignment();
> -	char *p;
> +	const char *p;
> +	int ret;
>  
>  	spin_lock(&resource_alignment_lock);
>  	p = resource_alignment_param;
> @@ -5477,58 +5559,21 @@ static resource_size_t pci_specified_resource_alignment(struct pci_dev *dev,
>  		} else {
>  			align_order = -1;
>  		}
> -		if (strncmp(p, "pci:", 4) == 0) {
> -			/* PCI vendor/device (subvendor/subdevice) ids are specified */
> -			p += 4;
> -			if (sscanf(p, "%hx:%hx:%hx:%hx%n",
> -				&vendor, &device, &subsystem_vendor, &subsystem_device, &count) != 4) {
> -				if (sscanf(p, "%hx:%hx%n", &vendor, &device, &count) != 2) {
> -					printk(KERN_ERR "PCI: Can't parse resource_alignment parameter: pci:%s\n",
> -						p);
> -					break;
> -				}
> -				subsystem_vendor = subsystem_device = 0;
> -			}
> -			p += count;
> -			if ((!vendor || (vendor == dev->vendor)) &&
> -				(!device || (device == dev->device)) &&
> -				(!subsystem_vendor || (subsystem_vendor == dev->subsystem_vendor)) &&
> -				(!subsystem_device || (subsystem_device == dev->subsystem_device))) {
> -				*resize = true;
> -				if (align_order == -1)
> -					align = PAGE_SIZE;
> -				else
> -					align = 1 << align_order;
> -				/* Found */
> -				break;
> -			}
> -		}
> -		else {
> -			if (sscanf(p, "%x:%x:%x.%x%n",
> -				&seg, &bus, &slot, &func, &count) != 4) {
> -				seg = 0;
> -				if (sscanf(p, "%x:%x.%x%n",
> -						&bus, &slot, &func, &count) != 3) {
> -					/* Invalid format */
> -					printk(KERN_ERR "PCI: Can't parse resource_alignment parameter: %s\n",
> -						p);
> -					break;
> -				}
> -			}
> -			p += count;
> -			if (seg == pci_domain_nr(dev->bus) &&
> -				bus == dev->bus->number &&
> -				slot == PCI_SLOT(dev->devfn) &&
> -				func == PCI_FUNC(dev->devfn)) {
> -				*resize = true;
> -				if (align_order == -1)
> -					align = PAGE_SIZE;
> -				else
> -					align = 1 << align_order;
> -				/* Found */
> -				break;
> -			}
> +
> +		ret = pci_dev_str_match(dev, p, &p);
> +		if (ret == 1) {
> +			*resize = true;
> +			if (align_order == -1)
> +				align = PAGE_SIZE;
> +			else
> +				align = 1 << align_order;
> +			break;
> +		} else if (ret < 0) {
> +			pr_info("PCI: Can't parse resource_alignment parameter: pci:%s\n",


The "pci:" prefix on %s doesn't make sense now, it was used above when
the pointer was already advanced past this token, now I believe it would
lead to "pci:pci:xxxx:yyyy" or "pci:xx:yy.z".  Thanks,

Alex