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Chapter 16 PC Card

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

16.1 Adding a device

The procedure for adding a new device to the list of supported pccard devices has changed from the system used through FreeBSD 4. In prior versions, editing a file in /etc to list the device was necessary. Starting in FreeBSD 5.0, devices drivers know what devices they support. There is now 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 information in the CIS of 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.

There is a widespread practice of one company developing a reference design for a PC Card product and then selling 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. However, the refinements to the physical card typically are very minor, if any changes are made at all. Often, however, to strengthen their branding of their version of the card, these vendors will place their company name in the human strings in the CIS space, but leave the manufacturer and product ids unchanged.

Because of the above practice, it is a smaller work load for FreeBSD to use the numeric IDs. It also introduces some minor complications into the process of adding IDs 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 from 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. Yet often, these devices will all have the same manufacturer and product id.

The PC Card bus keeps its 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 require that one matches them using 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 that are quite popular. 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 of the pccarddevs files. The first section lists the manufacturer numbers for those 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 those devices that use the string matching method. Finally, C-style comments 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:

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

shows the first few vendor ids. 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. There is the vendor keyword used to denote the kind of line that this is. There is the name of the vendor. This name will be repeated later in the pccarddevs file, as well as used in the driver's match tables, so keep it short and a valid C identifier. There is a numeric ID, in hex, for 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 you can see in the following example:

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

/* Archos */
product ARCHOS ARC_ATAPI    0x0043 MiniCD

the format is similar to the vendor lines. There is the product keyword. Then there is 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. There is then the product id for this card, in hex. As with the vendors, there is 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 as -1. -1 means “match anything you find” 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 we must match with string entries. This sections' format is a little different than 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

We have the familiar product keyword, followed by the vendor name followed by the card name, just as in the second section of the file. However, then we deviate from that format. 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 entries mean that that part of the entry should be ignored. In the example I have picked, there is a bad entry. It should not contain the version number in it 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[] = {
    PCMCIA_CARD(3COM, 3CRWE737A, 0),
    { 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 if you have a different table, the first element of the structure you have a table of be a struct pccard_product.

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. The baz is the expected function number that 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 the pccarddevs file. You may also see PCMCIA_CARD2 and PCMCIA_CARD2_D which are used when you need to match CIS 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

So, to add a new device, one must do the following steps. First, one must 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. You will likely see something like:

        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

as part of the output. The manufacturer and product are the numeric IDs for this product. While the cisvendor and cisproduct are the strings that are present in the CIS that describe this product.

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)

so we are good there. Looking for an entry for this card, we do not find one. 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

we can just add

product BUFFALO WLI2_CF_S11G   0x030c  BUFFALO AirStation ultra 802.11b CF

to pccarddevs. Presently, there is a manual step to regenerate the pccarddevs.h file used to convey these identifiers to the client driver. The following steps must be done before you can use them in the driver:

# cd src/sys/dev/pccard
# make -f Makefile.pccarddevs

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

static const struct pccard_product wi_pccard_products[] = {
    PCMCIA_CARD(3COM, 3CRWE737A, 0),
    { 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 try to see if it recognizes the device. If it does 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 it did not recognize it 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 that you need to worry about. First, you must commit the pccarddevs file to the tree. After you have done that, you must regenerate pccarddevs.h and commit it as a second commit (this is to make sure that the right $FreeBSD$ tag is in the latter file). Finally, you need to commit the additions to the driver.

16.1.5 Submitting a new device

Many people send entries for new devices to the author directly. Please do not do this. Please submit them as a PR and send the author the PR number for his records. This makes sure 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.

This, and other documents, can be downloaded from ftp://ftp.FreeBSD.org/pub/FreeBSD/doc/.

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For questions about this documentation, e-mail <doc@FreeBSD.org>.