Difference dma_alloc_coherent() in x86_32 and x86_64

[tochansky]

Hello!

I have a driver for PCI device which uses CMA framework for allocating 
big coherent blocks of memory for DMA.

Allocation looks like:

typedef struct {
 struct list_head list;
 uint32_t size8;
 void *kaddr;
 dma_addr_t paddr;
} dma_region_t;

LIST_HEAD(region_list);

..

void* AllocDMA( size_t size )
{
 dma_region_t *new_region;
 new_region = kmalloc(sizeof(dma_region_t), GFP_KERNEL);
 new_region->size8 = size;

 new_region->kaddr = dma_alloc_coherent( NULL, size, 
_region->paddr, GFP_KERNEL | GFP_DMA32 );

 list_add(_region->list, _list);
 printk("pcidev: cma_alloc paddr %pad kaddr %p size %d\n", 
_region->paddr, new_region->kaddr, new_region->size8);
 return new_region->kaddr;

}

It works fine on kernel 3.18.26 in 32bit mode.
When I reconfigure same kernel to run in 64bit mode(enabling in 
'menuconfig' option '64-bit kernel') and trying to use this driver with 
it
allocation failed with message in dmesg:
...
[ 1393.835535]  fallback device: swiotlb buffer is full (sz: 8388608 
bytes)
[ 1393.835579] pcidev: cma_alloc paddr 0x880234861220 kaddr  
  (null) size 8388608
...

My kernel command line is: swiotlb=16384 iommu=soft cma=256M


Anyone can explain this strange behavior?


-- 
D

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How to use uio_pci_generic driver.

[Dmitriy Tochansky]

Hello!
I have a problem writing application using uio subsystem.
As described at
http://www.kernel.org/doc/htmldocs/uio-howto.html#uio_pci_generic, I bind
my device to uio. Files in /sys/class/uio/uio0/ appears, dmesg say no
problems.
But when I trying to mmap regions of device file
/sys/class/uio/uio0/.../mapX not created.
A mmap part of code:

uint32_t UioMap(int devnum, int map_num)
{
char *u = (char *) calloc(64, 1);
sprintf(u, /sys/class/uio/uio%d/device/resource%d, devnum, map_num);
int fd = open(u, O_RDONLY);
if(fd  0)
{
fprintf(stderr,Error on open!\n);
return NULL;
}
else fprintf(stderr,fd = %d\n, fd);
void* map_addr = mmap(NULL,
0x80,
PROT_READ,
MAP_SHARED,
fd,
map_num * getpagesize());
if(map_addr == MAP_FAILED)
{
perror(mmap);
}
free(u);
return (uint32_t *) map_addr;
}

Is there any examples of usage uio_pci_generic in realworld?

-- 
Dmitriy
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