Hello All,



To understand DMA, I tried to implement sample dma module in x86 machine on (SUSE ). here is the code
<code>



#include <linux/module.h>

#include <linux/init.h>

#include <linux/kernel.h>

#include <linux/dma-mapping.h>

#include <linux/dmapool.h>

#include <linux/device.h>



static char *buffer= NULL;



static struct device *dev= NULL;

dma_addr_t mapping;



static int __init dma_init(void)

{

buffer = kmalloc(10, GFP_KERNEL);

if(buffer == NULL)

{

printk("kernel unbale to allocate memory for buffer\n");

return -1;

}

int ret = -1;

dev = kzalloc(sizeof(*dev), GFP_KERNEL);

if(dev == NULL)

{

kfree(buffer);

return -1;

}





dev_set_name(dev, "asht_dma");

ret = device_register(dev);

printk("device reg ret =%d\n", ret);

if(ret != 0)

{

kfree(buffer);

kfree(dev);

return -1;

}

if(dma_set_mask(dev, 0xffffffff))

{

printk("DMA supports\n");

}

else

{

printk("DMA Not Supported\n");

kfree(buffer);

kfree(dev);

return -1;



}

mapping = dma_map_single(dev, buffer, 10, DMA_TO_DEVICE);

if(mapping == NULL)

{

printk("dma_map_single is failed !!!!!!!!!");

kfree(buffer);

kfree(dev);

return 0;

}



dma_unmap_single(dev, mapping, 10, DMA_TO_DEVICE);





printk("dma modlule inserted\n");

return 0;

}





static void __exit dma_exit(void)

{



kfree(buffer);

//device_unregister(dev);

dma_unmap_single(dev, mapping, 10, DMA_TO_DEVICE);

kfree(dev);

printk("dma modlule removed\n");

}



module_init(dma_init);

module_exit(dma_exit);



MODULE_AUTHOR("ASHT");

MODULE_LICENSE("GPL");

</code>


#dmesg
device reg ret =0
DMA supports
BUG: unable to handle kernel NULL pointer dereference at 00000000
IP: [<c0109c8f>] nommu_map_single+0x36/0x97
*pdpt = 0000000037429001 *pde = 0000000000000000
Oops: 0000 [#1] SMP
last sysfs file: /sys/devices/virtual/net/lo/type
Modules linked in: dma1(N+) binfmt_misc(N) snd_pcm_oss(N) snd_mixer_oss(N) snd_seq(N) snd_seq_device(N) ipv6(N) i915(N) drm(N) af_packet(N) cpufreq_conservative(N) cpufreq_userspace(N) cpufreq_powersave(N) acpi_cpufreq(N) speedstep_lib(N) fuse(N) loop(N) dm_mod(N) snd_hda_intel(N) snd_pcm(N) snd_timer(N) snd_page_alloc(N) snd_hwdep(N) ppdev(N) snd(N) rtc_cmos(N) parport_pc(N) sr_mod(N) intel_agp(N) rtc_core(N) soundcore(N) button(N) agpgart(N) sg(N) i2c_i801(N) parport(N) serio_raw(N) pcspkr(N) rtc_lib(N) dcdbas(N) e1000e(N) cdrom(N) iTCO_wdt(N) i2c_core(N) iTCO_vendor_support(N) usbhid(N) hid(N) ff_memless(N) sd_mod(N) ehci_hcd(N) crc_t10dif(N) uhci_hcd(N) usbcore(N) edd(N) ext3(N) mbcache(N) jbd(N) fan(N) ide_pci_generic(N) ide_core(N) ahci(N) ata_generic(N) libata(N) scsi_mod(N) dock(N) thermal(N) processor(N) thermal_sys(N) hwmon(N)
Supported: No
Pid: 3948, comm: insmod Tainted: G (2.6.27.7-9-pae #1)
EIP: 0060:[<c0109c8f>] EFLAGS: 00010246 CPU: 0
EIP is at nommu_map_single+0x36/0x97
EAX: 00000000 EBX: f7d7f800 ECX: 00000000 EDX: 37dc8a6a
ESI: 37dc8a60 EDI: 00000000 EBP: 0000000a ESP: ee1adee8
DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068
Process insmod (pid: 3948, ti=ee1ac000 task=ee16c530 task.ti=ee1ac000)
Stack: 00000000 00000000 00000000 00000000 00000000 fffffffc 00000000 c050a300
fffffffc 00000000 f8cc5000 f8cc50e3 0000000a 00000001 f8c7e57c fffffffc
c010112b f557c7f4 00000001 f8c7e44c 00000026 00000000 00000000 f8c7e588
Call Trace:
[<f8cc50e3>] dma_init+0xe3/0x16f [dma1]
[<c010112b>] _stext+0x3b/0x127
[<c014ee38>] sys_init_module+0x8a/0x19e
[<c0104c1b>] sysenter_do_call+0x12/0x2f
[<ffffe430>] 0xffffe430
=======================
Code: ec 1c 8b 6c 24 30 85 ed 75 0f ba 21 00 00 00 b8 25 a5 41 c0 e8 ee 36 02 00 85 db 74 51 8b 83 f4 00 00 00 89 ea 31 c9 01 f2 11 f9 <8b> 18 8b 40 04 39 c1 72 3a 77 04 39 da 76 34 83 f8 00 77 05 83
EIP: [<c0109c8f>] nommu_map_single+0x36/0x97 SS:ESP 0068:ee1adee8
---[ end trace 9b56c809dd172d32 ]---


This seems I'm getting OOPS at dma_map_single, Please suggest how to solve this


Regards,
Ashok

Can you use dma_mapping_error on after dma_map_single? What is the result?

Hello archieval,

I used dma_mapping_error like

<code>
mapping = dma_map_single(dev, buffer, 10, DMA_TO_DEVICE);
if(mapping == NULL)
{
printk("dma_map_single is failed !!!!!!!!!");
kfree(buffer);
kfree(dev);
return 0;
}
ret = dma_mapping_error(dev, mapping);
printk("mapping_error =%d\n", ret);

</code>

its still oops while calling dma_map_single,

#dmesg shows

BUG: unable to handle kernel NULL pointer dereference at 00000000
IP: [<c0109c8f>] nommu_map_single+0x36/0x97
*pdpt = 000000002e148001 *pde = 0000000000000000
Oops: 0000 [#1] SMP

in dma_map_single() first argument is struct device *dev is this object initialization okay here in my progeram ??


Regards,
Ashok

Not sure about your initialization, what is the exact device that you are working on? You might want to initialize that depending on the device type. I am just looking on an example file in the linux source, drivers/parport/parport_pc.c in the function:

I actually have no experience on DMA in the kernel, I'm just making guess so most likely I am wrong also sorry.