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The simplest network driver

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# 8  
Old 11-23-2011
I have read "Linux Device Drivers", chapter "Network Drivers", and "PCI Drivers".
Thanks Corona688 for your response.

What if there are in kernel space two drivers supporting the same device id?
.probe function would be run for all of them?
# 9  
Old 11-23-2011
I haven't tried it, but my suspicion is that "probe" would be run for everything. Probing is how you detect non-plug-and-play things which don't advertise their presence, so PCI ID's wouldn't seem to apply.

But PCI drivers, usually not needing to probe, mostly don't probe at all. I think the PCI NE2000 network driver can, but has to be forced to do so by module options at load-time because blindly poking around at I/O addresses can be dangerous. Something unexpected might be occupying the bus resources it expects which could lock the PC or worse. On some IBM laptops, BIOS resources were found at addresses lm_sensors was expecting temperature sensors at, causing probes to brick the system!

One PCI ID for two drivers is a rare situation. Plug-and-play is supposed to be one model to one PCI ID, no ambiguity. If there's two drivers for the same ID, whichever gets loaded first wins. If they're built-in, whichever gets checked first on boot wins. Since the order of built-ins is arbitrary, if you want to control the order, you must make the drivers modules.

A rare situation but it still happens. There's two incompatible revisions of the old realtek 8139 network chip and two different linux kernel drivers -- 8139cp and 8139too. If you load the wrong one, it complains, and tells you to load the other in dmesg. Easy when they're modules, impossible when they're not.
Last edited by Corona688; 11-23-2011 at 12:38 PM..
# 10  
Old 11-23-2011
Quote:
Originally Posted by Corona688
I haven't tried it, but my suspicion is that "probe" would be run for everything. Probing is how you detect non-plug-and-play things which don't advertise their presence, so PCI ID's wouldn't seem to apply.
Setup:
- Intel network card
- e1000e standard linux driver in autorun
- myModule; customized e1000e driver by me for debugging reasons

Steps:
- after power on execute 'rmmod e1000e'
- 'insmod myModule'
From my debuging experience I see, that .probe function is fired always after 'insmod myModule' (when e1000e is not present).

Steps
- after power on do not remove 'e1000e' driver
- 'insmod myModule'
Now .probe function from myModule is not executed. Only init_module function operates.

What if I add myModule to autorun? Will .probe function be then executed? I don't know. I have no idea how to add myModule to autorun. Smilie.

I guess .probe is 'must be', because there are important lines like:

Code:
.probe function:
{
 netdev = alloc_etherdev
 SET_MODULE_OWNER(netdev);
  netdev->netdev_ops        = &e1000e_netdev_ops;
 err = register_netdev(netdev);
}

static const struct net_device_ops e1000e_netdev_ops = {
    .ndo_open        = e1000_open,    // e.g. ifconfig up
    .ndo_stop        = e1000_close,    // e.g. ifconfig down
    .ndo_start_xmit        = e1000_xmit_frame,
    .ndo_get_stats        = e1000_get_stats,
    .ndo_tx_timeout        = e1000_tx_timeout,
    .ndo_validate_addr    = eth_validate_addr,
};

Last edited by Chrisdot; 11-23-2011 at 01:29 PM..
# 11  
Old 11-23-2011
Quote:
Originally Posted by Chrisdot
Setup:
- Intel network card
- e1000e standard linux driver in autorun
- myModule; customized e1000e driver by me for debugging reasons

Steps:
- after power on execute 'rmmod e1000e'
- 'insmod myModule'
From my debuging experience I see, that .probe function is fired always after 'insmod myModule' (when e1000e is not present).

Steps
- after power on do not remove 'e1000e' driver
- 'insmod myModule'
Now .probe function from myModule is not executed. Only init_module function operates.
Your experience trumps my guess. Device ID's trump "probe". If you want to override/ignore PCI IDs, check out the PCI NE2000 driver.
Quote:
What if I add myModule to autorun?
To what?

The kernel doesn't care about which thing calls insmod/modprobe.

If you want to never load the intel one, add the intel one to modules.blacklist
# 12  
Old 11-24-2011
I have checked out PCI NE2000 driver:
LXR / The Linux Cross Reference
Do you mean using 'PCI_ANY_ID' ?
Code:
static DEFINE_PCI_DEVICE_TABLE(ne2k_pci_tbl) = {
        { 0x10ec, 0x8029, PCI_ANY_ID, PCI_ANY_ID, 0, 0, CH_RealTek_RTL_8029 },
        { 0x1050, 0x0940, PCI_ANY_ID, PCI_ANY_ID, 0, 0, CH_Winbond_89C940 },
        { 0x11f6, 0x1401, PCI_ANY_ID, PCI_ANY_ID, 0, 0, CH_Compex_RL2000 },
        { 0x8e2e, 0x3000, PCI_ANY_ID, PCI_ANY_ID, 0, 0, CH_KTI_ET32P2 },
        { 0x4a14, 0x5000, PCI_ANY_ID, PCI_ANY_ID, 0, 0, CH_NetVin_NV5000SC },
        { 0x1106, 0x0926, PCI_ANY_ID, PCI_ANY_ID, 0, 0, CH_Via_86C926 },
        { 0x10bd, 0x0e34, PCI_ANY_ID, PCI_ANY_ID, 0, 0, CH_SureCom_NE34 },
        { 0x1050, 0x5a5a, PCI_ANY_ID, PCI_ANY_ID, 0, 0, CH_Winbond_W89C940F },
        { 0x12c3, 0x0058, PCI_ANY_ID, PCI_ANY_ID, 0, 0, CH_Holtek_HT80232 },
        { 0x12c3, 0x5598, PCI_ANY_ID, PCI_ANY_ID, 0, 0, CH_Holtek_HT80229 },
        { 0x8c4a, 0x1980, PCI_ANY_ID, PCI_ANY_ID, 0, 0, CH_Winbond_89C940_8c4a },
        { 0, }

I tried myModule with 'PCI_ANY_ID'. It is visible in dmesg how myModule run .probe for few devices and failed trying to do 'ioremap' (inside .probe routine). Those are:
Code:
Host bridge: Intel Corporation 440FX - 82441FX PMC [Natoma] (rev 02)
Subsystem: Red Hat, Inc Qemu virtual machine
Flags: fast devsel

ISA bridge: Intel Corporation 82371SB PIIX3 ISA [Natoma/Triton II]
Subsystem: Red Hat, Inc Qemu virtual machine
Flags: medium devsel

Only for my Intel newtork card whole .probe routine went well.
Last edited by Chrisdot; 11-24-2011 at 05:56 AM..
# 13  
Old 11-29-2011
No, I don't. It was an option that had to be forced with insmod/modprobe like I said.

I don't see the right messages in that driver, it may be a different one. I'll look for it.

---------- Post updated at 09:48 AM ---------- Previous update was at 09:44 AM ----------

eepro.c has these lines:

Code:
                printk(KERN_WARNING "eepro_init_module: Probe is very dangerous in ISA boards!\n");
                printk(KERN_WARNING "eepro_init_module: Please add \"autodetect=1\" to force probe\n");
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