Chapter 16. PC Card

Table of Contents

This chapter will talk about the FreeBSD mechanisms for writing a device driver for a PC Card or CardBus device. However, at present it just documents how to add a new device to an existing pccard driver.

16.1. Adding a Device

Device drivers know what devices they support. There is a table of supported devices in the kernel that drivers use to attach to a device.

16.1.1. Overview

PC Cards are identified in one of two ways, both based on the Card Information Structure (CIS) stored on the card. The first method is to use numeric manufacturer and product numbers. The second method is to use the human readable strings that are also contained in the CIS. The PC Card bus uses a centralized database and some macros to facilitate a design pattern to help the driver writer match devices to his driver.

Original equipment manufacturers (OEMs) often develop a reference design for a PC Card product, then sell this design to other companies to market. Those companies refine the design, market the product to their target audience or geographic area, and put their own name plate onto the card. The refinements to the physical card are typically very minor, if any changes are made at all. To strengthen their brand, these vendors place their company name in the human readable strings in the CIS space, but leave the manufacturer and product IDs unchanged.

Due to this practice, FreeBSD drivers usually rely on numeric IDs for device identification. Using numeric IDs and a centralized database complicates adding IDs and support for cards to the system. One must carefully check to see who really made the card, especially when it appears that the vendor who made the card might already have a different manufacturer ID listed in the central database. Linksys, D-Link, and NetGear are a number of US manufacturers of LAN hardware that often sell the same design. These same designs can be sold in Japan under names such as Buffalo and Corega. Often, these devices will all have the same manufacturer and product IDs.

The PC Card bus code keeps a central database of card information, but not which driver is associated with them, in /sys/dev/pccard/pccarddevs. It also provides a set of macros that allow one to easily construct simple entries in the table the driver uses to claim devices.

Finally, some really low end devices do not contain manufacturer identification at all. These devices must be detected by matching the human readable CIS strings. While it would be nice if we did not need this method as a fallback, it is necessary for some very low end CD-ROM players and Ethernet cards. This method should generally be avoided, but a number of devices are listed in this section because they were added prior to the recognition of the OEM nature of the PC Card business. When adding new devices, prefer using the numeric method.

16.1.2. Format of pccarddevs

There are four sections in the pccarddevs files. The first section lists the manufacturer numbers for vendors that use them. This section is sorted in numerical order. The next section has all of the products that are used by these vendors, along with their product ID numbers and a description string. The description string typically is not used (instead we set the device’s description based on the human readable CIS, even if we match on the numeric version). These two sections are then repeated for devices that use the string matching method. Finally, C-style comments enclosed in / and / characters are allowed anywhere in the file.

The first section of the file contains the vendor IDs. Please keep this list sorted in numeric order. Also, please coordinate changes to this file because we share it with NetBSD to help facilitate a common clearing house for this information. For example, here are the first few vendor IDs:

vendor FUJITSU			0x0004  Fujitsu Corporation
vendor NETGEAR_2		0x000b  Netgear
vendor PANASONIC		0x0032	Matsushita Electric Industrial Co.
vendor SANDISK			0x0045	Sandisk Corporation

Chances are very good that the NETGEAR_2 entry is really an OEM that NETGEAR purchased cards from and the author of support for those cards was unaware at the time that Netgear was using someone else’s ID. These entries are fairly straightforward. The vendor keyword denotes the kind of line that this is, followed by the name of the vendor. This name will be repeated later in pccarddevs, as well as used in the driver’s match tables, so keep it short and a valid C identifier. A numeric ID in hex identifies the manufacturer. Do not add IDs of the form 0xffffffff or 0xffff because these are reserved IDs (the former is "no ID set" while the latter is sometimes seen in extremely poor quality cards to try to indicate "none"). Finally there is a string description of the company that makes the card. This string is not used in FreeBSD for anything but commentary purposes.

The second section of the file contains the products. As shown in this example, the format is similar to the vendor lines:

/* Allied Telesis K.K. */
product ALLIEDTELESIS LA_PCM	0x0002 Allied Telesis LA-PCM

/* Archos */
product	ARCHOS ARC_ATAPI	0x0043 MiniCD

The product keyword is followed by the vendor name, repeated from above. This is followed by the product name, which is used by the driver and should be a valid C identifier, but may also start with a number. As with the vendors, the hex product ID for this card follows the same convention for 0xffffffff and 0xffff. Finally, there is a string description of the device itself. This string typically is not used in FreeBSD, since FreeBSD’s pccard bus driver will construct a string from the human readable CIS entries, but it can be used in the rare cases where this is somehow insufficient. The products are in alphabetical order by manufacturer, then numerical order by product ID. They have a C comment before each manufacturer’s entries and there is a blank line between entries.

The third section is like the previous vendor section, but with all of the manufacturer numeric IDs set to -1, meaning "match anything found" in the FreeBSD pccard bus code. Since these are C identifiers, their names must be unique. Otherwise the format is identical to the first section of the file.

The final section contains the entries for those cards that must be identified by string entries. This section’s format is a little different from the generic section:

product ADDTRON AWP100		{ "Addtron", "AWP-100&spWireless&spPCMCIA", "Version&sp01.02", NULL }
product ALLIEDTELESIS WR211PCM	{ "Allied&spTelesis&spK.K.", "WR211PCM", NULL, NULL } Allied Telesis WR211PCM

The familiar product keyword is followed by the vendor name and the card name, just as in the second section of the file. Here the format deviates from that used earlier. There is a {} grouping, followed by a number of strings. These strings correspond to the vendor, product, and extra information that is defined in a CIS_INFO tuple. These strings are filtered by the program that generates pccarddevs.h to replace &sp with a real space. NULL strings mean that the corresponding part of the entry should be ignored. The example shown here contains a bad entry. It should not contain the version number unless that is critical for the operation of the card. Sometimes vendors will have many different versions of the card in the field that all work, in which case that information only makes it harder for someone with a similar card to use it with FreeBSD. Sometimes it is necessary when a vendor wishes to sell many different parts under the same brand due to market considerations (availability, price, and so forth). Then it can be critical to disambiguating the card in those rare cases where the vendor kept the same manufacturer/product pair. Regular expression matching is not available at this time.

16.1.3. Sample Probe Routine

To understand how to add a device to the list of supported devices, one must understand the probe and/or match routines that many drivers have. It is complicated a little in FreeBSD 5.x because there is a compatibility layer for OLDCARD present as well. Since only the window-dressing is different, an idealized version will be presented here.

static const struct pccard_product wi_pccard_products[] = {
	{ NULL }

static int
	device_t	dev;
	const struct pccard_product *pp;

	if ((pp = pccard_product_lookup(dev, wi_pccard_products,
	    sizeof(wi_pccard_products[0]), NULL)) != NULL) {
		if (pp->pp_name != NULL)
			device_set_desc(dev, pp->pp_name);
		return (0);
	return (ENXIO);

Here we have a simple pccard probe routine that matches a few devices. As stated above, the name may vary (if it is not foo_pccard_probe() it will be foo_pccard_match()). The function pccard_product_lookup() is a generalized function that walks the table and returns a pointer to the first entry that it matches. Some drivers may use this mechanism to convey additional information about some cards to the rest of the driver, so there may be some variance in the table. The only requirement is that each row of the table must have a struct pccard_product as the first element.

Looking at the table wi_pccard_products, one notices that all the entries are of the form PCMCIA_CARD(foo, bar, baz). The foo part is the manufacturer ID from pccarddevs. The bar part is the product ID. baz is the expected function number for this card. Many pccards can have multiple functions, and some way to disambiguate function 1 from function 0 is needed. You may see PCMCIA_CARD_D, which includes the device description from pccarddevs. You may also see PCMCIA_CARD2 and PCMCIA_CARD2_D which are used when you need to match both CIS strings and manufacturer numbers, in the "use the default description" and "take the description from pccarddevs" flavors.

16.1.4. Putting it All Together

To add a new device, one must first obtain the identification information from the device. The easiest way to do this is to insert the device into a PC Card or CF slot and issue devinfo -v. Sample output:

        cbb1 pnpinfo vendor=0x104c device=0xac51 subvendor=0x1265 subdevice=0x0300 class=0x060700 at slot=10 function=1
            unknown pnpinfo manufacturer=0x026f product=0x030c cisvendor="BUFFALO" cisproduct="WLI2-CF-S11" function_type=6 at function=0

manufacturer and product are the numeric IDs for this product, while cisvendor and cisproduct are the product description strings from the CIS.

Since we first want to prefer the numeric option, first try to construct an entry based on that. The above card has been slightly fictionalized for the purpose of this example. The vendor is BUFFALO, which we see already has an entry:

vendor BUFFALO			0x026f	BUFFALO (Melco Corporation)

But there is no entry for this particular card. Instead we find:

product BUFFALO WLI_PCM_S11	0x0305	BUFFALO AirStation 11Mbps WLAN
product	BUFFALO	LPC3_CLT	0x030a	BUFFALO LPC3-CLT Ethernet Adapter
product BUFFALO WLI_CF_S11G	0x030b	BUFFALO AirStation 11Mbps CF WLAN

To add the device, we can just add this entry to pccarddevs:

product BUFFALO WLI2_CF_S11G	0x030c	BUFFALO AirStation ultra 802.11b CF

Once these steps are complete, the card can be added to the driver. That is a simple operation of adding one line:

static const struct pccard_product wi_pccard_products[] = {
	{ NULL }

Note that I have included a ‘+’ in the line before the line that I added, but that is simply to highlight the line. Do not add it to the actual driver. Once you have added the line, you can recompile your kernel or module and test it. If the device is recognized and works, please submit a patch. If it does not work, please figure out what is needed to make it work and submit a patch. If the device is not recognized at all, you have done something wrong and should recheck each step.

If you are a FreeBSD src committer, and everything appears to be working, then you can commit the changes to the tree. However, there are some minor tricky things to be considered. pccarddevs must be committed to the tree first. Then pccarddevs.h must be regenerated and committed as a second step, ensuring that the right $FreeBSD$ tag is in the latter file. Finally, commit the additions to the driver.

16.1.5. Submitting a New Device

Please do not send entries for new devices to the author directly. Instead, submit them as a PR and send the author the PR number for his records. This ensures that entries are not lost. When submitting a PR, it is unnecessary to include the pccardevs.h diffs in the patch, since those will be regenerated. It is necessary to include a description of the device, as well as the patches to the client driver. If you do not know the name, use OEM99 as the name, and the author will adjust OEM99 accordingly after investigation. Committers should not commit OEM99, but instead find the highest OEM entry and commit one more than that.

Last modified on: March 9, 2024 by Danilo G. Baio