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Old 09-07-2011, 04:43 AM   #1
leechaotang
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How to emulate a PCI device in Linux

Hi,

I want to emulate a PCI express device in Linux, how should I do it?

i.e. there is no real hardware PCI express in system, but I want Linux to act as there is a
PCI express device there. How to do it?

Thanks!

Mark
 
Old 09-07-2011, 01:18 PM   #2
frieza
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first of all, what kind of device are you trying to emulate and for what purpose?
i've never tried doing this myself but i would start by looking at how other hardware device drivers access hardware as well as download a few emulators such as qemu to figure out how they emulate hardware, learn how to write a kernel module that emulates the hardware device and produces a device node in /dev
but how you do it depends on what you are doing and your purpose.
 
Old 09-10-2011, 05:38 AM   #3
robvoo
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Hi frieza,

You should first think about the following, how do you want to interface to your PCI device?
It is possible to create a stub driver which you can access with device operations like
(read, write, mmap, ioctls) from user space.

Don't know if it is possible to emulate a real pci device with a kernel module
because this is handled by the PCI subsystem.

What is the purpose of the simulated device?

Regards Rob
 
Old 09-16-2011, 02:40 AM   #4
osmiy
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Lightbulb Try to create dummy PCI bus.
As far as I tried, the simplest way is to create the dummy PCI bus with custom read/write handlers.

See the `pci_scan_bus` usage.

I tried that code for x86 platform.

Code:
   #define MY_PCI_DOMAIN_NUM 0x0001
   #define MY_PCI_BUS_NUM 0x00

   struct pci_bus my_pci_bus = NULL;
   struct pci_sysdata my_pci_sd;

   memset (&my_pci_sd, 0 sizeof (my_pci_sd));
   my_pci_sd.domain = MY_PCI_DOMAIN_NUM;
   my_pci_sd.node = -1;

   memset (&my_pci_ops, 0, sizeof (my_pci_ops));
   my_pci_ops.read = my_pci_read;
   my_pci_ops.write = my_pci_write;

   my_pci_bus = pci_scan_bus(MY_PCI_BUS_NUM, &my_pci_ops, NULL);

   if (my_pci_bus)
   {
      printk (KERN_INFO "Successfully created MY PCI bus");
   }
You should implement the `my_pci_read` and `my_pci_write` to emulate PCI device responses, according to the PCI standard.

I'm not sure that is right solution, but it works on my side.
 
Old 03-18-2015, 05:34 AM   #5
neel.basu
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Registered: Mar 2015
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I know the thread is old. But I have to create a fake PCI device with custom read/write function. I am trying to replicate this example and hitting errors. Can you please post an working demo ?

I was getting compilation errors on
Code:
struct pci_bus my_pci_bus = NULL;
so I changed that to
Code:
struct pci_bus my_pci_bus = {};
This is my current code

Code:
#define MY_PCI_DOMAIN_NUM 0x0001
#define MY_PCI_BUS_NUM 0x00

#include <linux/pci.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/init.h>
#include <linux/module.h>

int pci_read(struct pci_bus *bus, unsigned int devfn, int where, int size, u32 *val){
  return 0;
}
int pci_write(struct pci_bus *bus, unsigned int devfn, int where, int size, u32 val){
  return 0;
}

struct pci_ops my_pci_ops = {};

int pci_bus_match(struct device *dev, struct device_driver *drv){
  return 0;
}

struct bus_type pci_bus_type = {
       name:	"pci",
       match:	pci_bus_match,
};

extern struct bus_type pci_bus_type;

MODULE_LICENSE("Dual BSD/GPL");

struct pci_bus my_pci_bus = {};
struct pci_sysdata my_pci_sd;
// 
// memset (&my_pci_sd, 0 sizeof (my_pci_sd));
// my_pci_sd.domain = MY_PCI_DOMAIN_NUM;
// my_pci_sd.node = -1;
// 


static int hello_init(void){
    struct pci_bus* my_pci_bus;
    
    printk(KERN_ALERT "Hello, world\n");
    memset (&my_pci_ops, 0, sizeof (my_pci_ops));
    my_pci_ops.read = pci_read;
    my_pci_ops.write = pci_write;
    
    my_pci_bus = pci_scan_bus(MY_PCI_BUS_NUM, &my_pci_ops, NULL);
    if(my_pci_bus){
      printk(KERN_INFO "Successfully created MY PCI bus");
    }
    return 0;
}

static void hello_exit(void)
{
    printk(KERN_ALERT "Goodbye, cruel world\n");
}

module_init(hello_init);
module_exit(hello_exit);
after I do `sudo insmod pci` I don not get any new device in lspci. and dmesg is full of traces

Code:
[15516.161020] BUG: unable to handle kernel NULL pointer dereference at           (null)
[15516.164054] IP: [<ffffffff813ba983>] pci_create_root_bus+0x73/0x440
[15516.165495] PGD 106bc6067 PUD 1230ed067 PMD 0 
[15516.166922] Oops: 0000 [#1] SMP 
[15516.168340] Modules linked in: pci(OE+) cdc_acm uas usb_storage vhost_net vhost macvtap macvlan fuse ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat nf_nat_ipv4 nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack xt_CHECKSUM iptable_mangle tun bridge stp llc ip6table_filter ip6_tables ebtable_nat ebtables bnep bluetooth vfat fat uvcvideo videobuf2_vmalloc videobuf2_core videobuf2_memops v4l2_common videodev media rtsx_pci_ms memstick rtsx_pci_sdmmc mmc_core kvm_amd kvm hp_wmi sparse_keymap crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel arc4 rt2800pci rt2800mmio rt2800lib rt2x00pci rt2x00mmio rt2x00lib hp_accel eeprom_93cx6 lis3lv02d mac80211 input_polldev cfg80211 crc_ccitt microcode joydev serio_raw k10temp snd_hda_codec_idt snd_hda_codec_generic rtsx_pci mfd_core
[15516.169995]  video
[15516.169996]  snd_hda_codec_hdmi
[15516.169996]  snd_hda_intel
[15516.169997]  snd_hda_controller
[15516.169998]  snd_hda_codec
[15516.169999]  snd_hwdep
[15516.169999]  snd_seq
[15516.170000]  snd_seq_device
[15516.170001]  snd_pcm
[15516.170001]  rfkill
[15516.170002]  i2c_piix4
[15516.170003]  acpi_cpufreq
[15516.170003]  snd_timer
[15516.170004]  snd
[15516.170006]  soundcore
[15516.170007]  shpchp
[15516.170008]  wmi
[15516.170008]  hp_wireless
[15516.170009]  binfmt_misc
[15516.170010]  nfsd
[15516.170010]  auth_rpcgss
[15516.170011]  nfs_acl
[15516.170012]  lockd
[15516.170013]  grace
[15516.170014]  sunrpc
[15516.170014]  radeon
[15516.170015]  r8169
[15516.170016]  mii
[15516.170017]  i2c_algo_bit
[15516.170018]  drm_kms_helper
[15516.170018]  ttm
[15516.170019]  drm
[15516.170020]  [last unloaded: hello_printk]

[15516.170024] CPU: 3 PID: 1738 Comm: insmod Tainted: G           OE  3.18.7-100.fc20.x86_64 #1
[15516.170026] Hardware name: Hewlett-Packard HP Pavilion g6 Notebook PC/184A, BIOS F.26 02/21/2013
[15516.170028] task: ffff88014ada6220 ti: ffff880103854000 task.ti: ffff880103854000
[15516.170030] RIP: 0010:[<ffffffff813ba983>] 
[15516.170033]  [<ffffffff813ba983>] pci_create_root_bus+0x73/0x440
[15516.170035] RSP: 0018:ffff880103857bf8  EFLAGS: 00010286
[15516.170037] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
[15516.170038] RDX: ffff88000ffaf870 RSI: 0000000000000000 RDI: ffff88000ffafc00
[15516.170039] RBP: ffff880103857c98 R08: 0000000000000000 R09: ffff8801a8801500
[15516.170040] R10: 000000000ffaf801 R11: ffff8801038579ce R12: ffff88000ffaf800
[15516.170041] R13: 0000000000000000 R14: ffffffffa0851710 R15: 0000000000000000
[15516.170044] FS:  00007f1bc7f75740(0000) GS:ffff8801aed80000(0000) knlGS:00000000f45ffb40
[15516.170045] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[15516.170046] CR2: 0000000000000000 CR3: 0000000133833000 CR4: 00000000000407e0
[15516.170048] Stack:
[15516.170048]  000000000000000c
[15516.170050]  0000000000000006
[15516.170050]  ffff880103857c88
[15516.170051]  ffff880103857cb0

[15516.170052]  ffff8801a8801c00
[15516.170053]  ffffffff813b8131
[15516.170054]  ffff880057c68920
[15516.170054]  ffff880103857cb0

[15516.170056]  ffffffff81cac360
[15516.170056]  ffff880103857cb0
[15516.170057]  ffffffff81cac360
[15516.170057]  0000000000000000

[15516.170059] Call Trace:

[15516.170065]  [<ffffffff813b8131>] ? pci_add_resource_offset+0x31/0x70

[15516.170071]  [<ffffffff813bb7c8>] pci_scan_bus+0x78/0xc0

[15516.170075]  [<ffffffffa084f030>] ? pci_bus_match+0x10/0x10 [pci]

[15516.170079]  [<ffffffffa084f06d>] hello_init+0x3d/0x60 [pci]

[15516.170083]  [<ffffffff81002144>] do_one_initcall+0xd4/0x210

[15516.170088]  [<ffffffff811cf192>] ? __vunmap+0xc2/0x110

[15516.170093]  [<ffffffff811152ab>] load_module+0x1cab/0x2730

[15516.170096]  [<ffffffff81110f00>] ? store_uevent+0x70/0x70

[15516.170101]  [<ffffffff8120ef70>] ? kernel_read+0x50/0x80

[15516.170106]  [<ffffffff81115ee6>] SyS_finit_module+0xa6/0xd0

[15516.170112]  [<ffffffff8174cfa9>] system_call_fastpath+0x12/0x17
[15516.170114] Code: 
[15516.170115] c4 
[15516.170115] 0f 
[15516.170116] 84 
[15516.170116] 21 
[15516.170117] 03 
[15516.170118] 00 
[15516.170118] 00 
[15516.170119] 4c 
[15516.170119] 89 
[15516.170120] a8 
[15516.170120] c8 
[15516.170121] 00 
[15516.170121] 00 
[15516.170122] 00 
[15516.170122] 4c 
[15516.170123] 89 
[15516.170123] b0 
[15516.170124] b8 
[15516.170124] 00 
[15516.170125] 00 
[15516.170126] 00 
[15516.170126] 49 
[15516.170127] 63 
[15516.170127] c7 
[15516.170128] 49 
[15516.170128] 89 
[15516.170129] 84 
[15516.170129] 24 
[15516.170130] 80 
[15516.170130] 00 
[15516.170131] 00 
[15516.170132] 00 
[15516.170132] 41 
[15516.170133] 88 
[15516.170133] 84 
[15516.170134] 24 
[15516.170134] d8 
[15516.170135] 00 
[15516.170135] 00 
[15516.170136] 00 
[15516.170136] 44 
[15516.170137] 89 
[15516.170137] fe 
[15516.170138] <41> 
[15516.170139] 8b 
[15516.170139] 7d 
[15516.170140] 00 
[15516.170140] e8 
[15516.170141] b4 
[15516.170141] 8a 
[15516.170142] 00 
[15516.170142] 00 
[15516.170143] 48 
[15516.170144] 85 
[15516.170144] c0 
[15516.170145] 74 
[15516.170145] 3f 
[15516.170146] f6 
[15516.170146] 05 
[15516.170147] ba 
[15516.170147] cc 
[15516.170148] 94 
[15516.170148] 00 
[15516.170149] 04 

[15516.170150] RIP 
[15516.170153]  [<ffffffff813ba983>] pci_create_root_bus+0x73/0x440
[15516.170154]  RSP <ffff880103857bf8>
[15516.170155] CR2: 0000000000000000
[15516.179558] ---[ end trace d99a70d9357a4b3b ]---
Thank You
Last edited by neel.basu; 03-18-2015 at 06:16 AM.
 
  


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