Re: Getting to the bottom of the Dreamcast DMA issue

[Adrian M. <ad...@ne...>]

More on this... 

Code seemed to be failing on this:

if (atomic_xchg(&channel->busy, 1))

atomic_xchg expands out to this:

#define atomic_xchg(v, new) (xchg(&((v)->counter), new))

and in sh xchg expands out to this:

#define xchg(ptr,x)     \
        ((__typeof__(*(ptr)))__xchg((ptr),(unsigned long)(x), sizeof(*(ptr))))

But this has a slightly different format in other archs - eg i386:

#define xchg(ptr,v) ((__typeof__(*(ptr)))__xchg((unsigned long)(v),(ptr),sizeof(*(ptr))))

arm -

#define xchg(ptr,x) \
         ((__typeof__(*(ptr)))__xchg((unsigned long)(x),(ptr),sizeof(*(ptr))))

MIPS

#define xchg(ptr,x) ((__typeof__(*(ptr)))__xchg((unsigned long)(x),(ptr),sizeof(*(ptr))))

So I wondered if it was the reversal of the params that was the issue and did this quick and very dirty hack ---
#define xchg(ptr,x)	\
	((__typeof__(*(ptr)))__xchg((ptr),(unsigned long)(x), sizeof(*(ptr))))

#define xchg_dma(ptr, x)  \
	((__typeof__(*(ptr)))__xchg((unsigned long)(x),(ptr),sizeof(*(ptr))))

and changing atomic_chg to this:

#define atomic_xchg(v, new) (xchg_dma(&((v)->counter), new))


But, as with most quick and dirty hacks, it didn't work...
Linux version 2.6.22-gc2dc1ad5-dirty (adrian@bossclass) (gcc version 3.4.6) #12 PREEMPT Mon Jul 16 23:16:34 BST 2007
console [sercon0] enabled
Booting machvec: Sega Dreamcast
Node 0: start_pfn = 0xc000, low = 0xd000
Zone PFN ranges:
  Normal      49152 ->    53248
early_node_map[1] active PFN ranges
    0:    49152 ->    53248
Built 1 zonelists in Zone order.  Total pages: 4064
Kernel command line: console=ttySC1,115200 panic=3 root=/dev/nfs rw nfsaddrs=192.168.61.55:192.168.61.50:192.168.61.50: earlyprintk=serial
PID hash table entries: 64 (order: 6, 256 bytes)
Using tmu for system timer
Using 12.469 MHz high precision timer.
Console: colour dummy device 80x25
Dentry cache hash table entries: 2048 (order: 1, 8192 bytes)
Inode-cache hash table entries: 1024 (order: 0, 4096 bytes)
Memory: 14104k/16384k available (1499k kernel code, 444k data, 72k init)
PVR=040205c1 CVR=00000000 PRR=00000000
I-cache : n_ways=1 n_sets=256 way_incr=8192
I-cache : entry_mask=0x00001fe0 alias_mask=0x00001000 n_aliases=2
D-cache : n_ways=1 n_sets=512 way_incr=16384
D-cache : entry_mask=0x00003fe0 alias_mask=0x00003000 n_aliases=4
Mount-cache hash table entries: 512
CPU: SH7750
NET: Registered protocol family 16
DMA: Registering DMA API.
DMA: Registering sh_dmac handler (4 channels).
Fault in unaligned fixup: 0000 [#1]
Modules linked in:

Pid : 1, Comm:              swapper
PC is at request_dma+0x2e/0x88
PC  : 8c10d66a SP  : 8c255f30 SR  : 400000f1 TEA : 00000001    Not tainted
R0  : 00000000 R1  : 00000001 R2  : 8c24c538 R3  : 40000001
R4  : 00000084 R5  : 00000084 R6  : 00000004 R7  : 8c24c400
R8  : 8c24c508 R9  : 00000000 R10 : 8c1e22f0 R11 : 8c1b2fec
R12 : 00000000 R13 : 8c1fb370 R14 : 00000000
MACH: 00000000 MACL: 00000108 GBR : 00000000 PR  : 8c10d656

Call trace: 
[<8c1f403a>] pvr2_dma_init+0x12/0x34
[<8c1ea848>] kernel_init+0x90/0x244
[<8c0035e4>] kernel_thread_helper+0x4/0x10
[<8c1ea7b8>] kernel_init+0x0/0x244
[<8c0035e0>] kernel_thread_helper+0x0/0x10

Process: swapper (pid: 1, stack limit = 8c254001)
Stack: (0x8c255f30 to 0x8c256000)
5f20:                                     8c1f403a 00000000 00000000 00000000 
5f40: 00000000 8c1ea848 00000000 00000000 00000000 00000000 00000000 00000000 
5f60: 00000000 00000000 00000000 00000000 00000001 00000000 00000000 00000000 
5f80: 8c0035e4 00000000 00000000 00000000 00000000 00000000 00000000 00000000 
5fa0: 00000000 00000000 00000000 00000000 00000000 8c1ea7b8 00000000 00000000 
5fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 8c255fa0 
5fe0: 8c0035e0 00000000 40000000 00000000 00000000 00000000 00000000 00000000 
Kernel panic - not syncing: Attempted to kill init!
Rebooting in 3 seconds..