[maemo-developers] ARM MMU questions

[From: Simon Pickering]

>> If I try to name my memory section FRAMEBUFFER (same code, just changing
>> the name in the command file), I'm back to the original problematic sort
>> of output:

<snip>

> Well it makes sense this is really a special case since (at least on
> 770) you don't want to map just any random memory, you want to map
> _framebuffer_ memory (i.e. specific memory preallocated in bootloader
> and used by omapfb driver). It doesn't explain why the mapping should be
> done differently on DSP side but it is definitely handled as a special
> case in kernel so it needs special keyword. With different name you get
> some random memory not related to video (thus you need to do additional
> copy to real video memory on ARM side).

Of course, I'd just not realised that the name of the memory section 
was used to perform the framebuffer sharing. I had expected to have to 
make an explicit call to the DSP memory ioctl to do this. It hopefully 
makes life easier. I'll have to try modifying my N800 framebuffer test 
code to remove the (duplicate) ioctl calls I was making and see if that 
produces any different results.

>> Another thing I need to look at is whether I can share some large shared
>> memory regions on the 770 at higher addresses in the DSP memory map (to
>> be used by mplayer to avoid memcpy operations on frames).
>
> Well that would be nice but most probably you need continuous physical
> (not virtual) memory for this so the frame can be used as real video
> memory = transferable via DMA to external video chip.

This is probably not such a big issue - the idea here is to share some 
memory buffers between mplayer and the DSP so mplayer can fill them 
(and then use them to calculate the next frames, etc.) and the DSP can 
be told to display the data in one of these buffers (after it performs 
colourspace conversion and scaling). There will be some memcpys on the 
DSP side (from shared memory to framebuffer), but hopefully this will 
be fast enough as the DSP does not have to do anything else.

With that said, I've just been trying to use large (0x200000 8-bit 
bytes) buffers on the 770, and am getting a new error:

MEMORY {

    PAGE 0:     EXTMEM9:  origin = 0x600000, len = 0x200000
}


SECTIONS {
         sharedmem_mmap_buffer > EXTMEM9 /*must start at beginning of page */

}

with a 0x100000 (16-bit) byte array on the DSP-side (i.e. two pages and TLBs).

dsp_dld output:

device sharedmem is requesting for TADD.
starting TADD process for device sharedmem.
loading /lib/dsp/modules/sharedmem.o.
mapping external memory: adr = 0x600000, size = 0x200000
adding _task_sharedmem(@11a004) into system.
receiving signal 17
poll error
sending SIGBUS signal to all task users...
killing pid 1045.
killing pid 1043.
killing pid 1044.
killing pid 1143.
Failed to stop some DSP user processes.
rmdev pcm2
rmdev aacdec
rmdev amrnb
rmdev amrwb
rmdev mp3dec
rmdev mpeg4dec
rmdev videofb
rmdev mp2dec
rmdev pcm_rec
rmdev aep
rmdev g711_enc
rmdev g711_dec
rmdev ilbc_enc
rmdev ilbc_dec
rmdev demo_console
rmdev demo_fb
rmdev hellotimer
rmdev framebuffer
rmdev sharedmem
releasing resources for DSP
DSP reset
releasing external memory map: adr = 0x100000
releasing external memory map: adr = 0x028000
releasing external memory map: adr = 0x300000
releasing external memory map: adr = 0x400000
releasing external memory map: adr = 0x600000
status = 3
restarting.

and dmesg:

[96562.654235] omapdsp: mapping in ARM MMU, v=0xe0600000, p=0x10400000, 
sz=0x100000
[96562.654541] omapdsp: mapping in ARM MMU, v=0xe0700000, p=0x10500000, 
sz=0x100000
[96563.865417] dsp_taskmod_busy(): sharedmem is in ADDREQ
[96563.865509] omapdsp: tasks are busy.
[96563.865600] omapdsp: unmapping in ARM MMU, v=0xe0100000, sz=0x100000
[96563.865814] omapdsp: freeing 0x100000 bytes @ adr 0xc2b00000
[96563.865875] omapdsp: unmapping in ARM MMU, v=0xe0200000, sz=0x100000
[96563.866058] omapdsp: freeing 0x100000 bytes @ adr 0xc2a00000
[96563.866088] omapdsp: unmapping in ARM MMU, v=0xe0028000, sz=0x1000
[96563.866149] omapdsp: freeing 0x1000 bytes @ adr 0xc2456000
[96563.866210] omapdsp: unmapping in ARM MMU, v=0xe0300000, sz=0x100000
[96563.866333] omapfb_unregister_client(): success
[96563.866394] omapdsp: unmapping in ARM MMU, v=0xe0400000, sz=0x100000
[96563.866607] omapdsp: freeing 0x100000 bytes @ adr 0xc2900000
[96563.866668] omapdsp: unmapping in ARM MMU, v=0xe0500000, sz=0x10000
[96563.866729] omapdsp: freeing 0x10000 bytes @ adr 0xc2410000
[96563.866790] omapdsp: unmapping in ARM MMU, v=0xe0510000, sz=0x10000
[96563.866851] omapdsp: freeing 0x10000 bytes @ adr 0xc2400000
[96563.866912] omapdsp: unmapping in ARM MMU, v=0xe0520000, sz=0x10000
[96563.866973] omapdsp: freeing 0x10000 bytes @ adr 0xc28f0000
[96563.867034] omapdsp: unmapping in ARM MMU, v=0xe0530000, sz=0x10000
[96563.867095] omapdsp: freeing 0x10000 bytes @ adr 0xc28e0000
[96563.867156] omapdsp: unmapping in ARM MMU, v=0xe0540000, sz=0x10000
[96563.867218] omapdsp: freeing 0x10000 bytes @ adr 0xc28d0000
[96563.867248] omapdsp: unmapping in ARM MMU, v=0xe0550000, sz=0x10000
[96563.867340] omapdsp: freeing 0x10000 bytes @ adr 0xc28c0000
[96563.867370] omapdsp: unmapping in ARM MMU, v=0xe0560000, sz=0x10000
[96563.867462] omapdsp: freeing 0x10000 bytes @ adr 0xc2460000
[96563.867523] omapdsp: unmapping in ARM MMU, v=0xe0570000, sz=0x10000
[96563.867584] omapdsp: freeing 0x10000 bytes @ adr 0xc2470000
[96563.867645] omapdsp: unmapping in ARM MMU, v=0xe0600000, sz=0x100000
[96563.867889] omapdsp: freeing 0x100000 bytes @ adr 0xc0400000
[96563.867950] omapdsp: unmapping in ARM MMU, v=0xe0700000, sz=0x100000
[96563.868194] omapdsp: freeing 0x100000 bytes @ adr 0xc0500000
[96563.869567] omapdsp: mapping in ARM MMU, v=0xe0fff000, p=0x13c00000, 
sz=0x1000
[96563.910156] omapdsp: mapping in ARM MMU, v=0xe0100000, p=0x12900000, 
sz=0x100000
[96563.910430] omapdsp: mapping in ARM MMU, v=0xe0200000, p=0x12a00000, 
sz=0x100000
[96563.910766] omapdsp: mapping in ARM MMU, v=0xe0028000, p=0x13521000, 
sz=0x1000
[96563.910888] omapdsp: frame buffer export
[96563.910949] omapdsp: mapping in ARM MMU, v=0xe0300000, p=0x13d00000, 
sz=0x100000
[96563.911132] omapfb_notifier_cb(): event = READY
[96563.911224] omapfb_register_client(): success
[96563.911468] omapdsp: mapping in ARM MMU, v=0xe0400000, p=0x12b00000, 
sz=0x100000
[96563.911682] omapdsp: mapping in ARM MMU, v=0xe0500000, p=0x128c0000, 
sz=0x10000
[96563.911773] omapdsp: mapping in ARM MMU, v=0xe0510000, p=0x128d0000, 
sz=0x10000
[96563.911834] omapdsp: mapping in ARM MMU, v=0xe0520000, p=0x128e0000, 
sz=0x10000
[96563.911926] omapdsp: mapping in ARM MMU, v=0xe0530000, p=0x128f0000, 
sz=0x10000
[96563.912017] omapdsp: mapping in ARM MMU, v=0xe0540000, p=0x12400000, 
sz=0x10000
[96563.912109] omapdsp: mapping in ARM MMU, v=0xe0550000, p=0x12410000, 
sz=0x10000
[96563.912200] omapdsp: mapping in ARM MMU, v=0xe0560000, p=0x12600000, 
sz=0x10000
[96563.912292] omapdsp: mapping in ARM MMU, v=0xe0570000, p=0x10690000, 
sz=0x10000

After the mapping we get something along these lines:

[96404.687469] omapdsp: DSP has been already configured. do unconfig!

and it tries to unmap and start again. After a couple of failures we 
get a reboot.

I need to look into why the DSP task is hanging and see what the kernel 
messages indicate. Something to keep me occupied :)

Cheers,


Simon