[poky] BeagleBoard using GCC 4.6.0

[Darren Hart]

On 06/08/2011 11:20 AM, Saul Wold wrote:
> On 06/08/2011 10:43 AM, Gary Thomas wrote:
>> Now that Poky is using GCC 4.6.0, has anyone actually checked the
>> operation on the BeagleBoard? I suspect that you'll find that the
>> EHCI USB does not work. I can't really check here as I don't trust
>> the EHCI on my BeagleBoard rev C3 (not xM).
>>
>> That said, I've tried this new compiler (previously reported) on
>> my own OMAP/3530 board which uses the same 2.6.37 kernel (just not
>> the linux-yocto version). When I build my kernel with GCC 4.5.2,
>> it works perfectly, but fails with GCC 4.6.0 (I trust the hardware).
>>
>> I've isolated it down to at least the function 'ehci_hub_control'
>> (but I suspect the problem is more fundamental). Comparing the code
>> generated by the two compilers with the same source tree, this function
>> is dramatically different. I can see why it's failing, I just don't
>> know why the compiler is doing what it's doing.
>>
> 
> Gary,
> 
> I am not sure if Khem Raj is on this list, so I am forwarding it to him, 
> he might have some insight.

By switching GCCVERSION to 4.5.1, a kernel that previously failed to
bring up the USB hub on the beagleboard xM (and the ethernet port) with
4.6.0, now successfully does so. Unfortunatley, the framebuffer device
fails now. Any hints from the compiler crowd on things to try? Or output
we can collect to help resolve this?

--
Darren

> 
> Sau!
> 
> 
>> The lines at drivers/usb/host/ehci-hub.c:841
>> case GetPortStatus:
>> if (!wIndex || wIndex > ports)
>> goto error;
>> wIndex--;
>> status = 0;
>> temp = ehci_readl(ehci, status_reg);
>>
>> are being compiled very differently.
>>
>> With GCC 4.5.2:
>> 0xc0229810 <ehci_hub_control+672>: cmp r3, #0 ; 0x0
>> 0xc0229814 <ehci_hub_control+676>: beq 0xc0229df8 <ehci_hub_control+2184>
>> 0xc0229818 <ehci_hub_control+680>: cmp r3, r0
>> 0xc022981c <ehci_hub_control+684>: bgt 0xc0229df8 <ehci_hub_control+2184>
>> 0xc0229820 <ehci_hub_control+688>: sub r8, r3, #1 ; 0x1
>> 0xc0229824 <ehci_hub_control+692>: ldr r5, [r7, #4]
>> 0xc0229828 <ehci_hub_control+696>: uxth r8, r8
>> 0xc022982c <ehci_hub_control+700>: dmb sy
>>
>> With GCC 4.6.0:
>> 0xc0221630 <ehci_hub_control+808>: cmp r3, #0 ; 0x0
>> 0xc0221634 <ehci_hub_control+812>: beq 0xc0221d7c <ehci_hub_control+2676>
>> 0xc0221638 <ehci_hub_control+816>: cmp r3, r0
>> 0xc022163c <ehci_hub_control+820>: bgt 0xc0221d7c <ehci_hub_control+2676>
>> 0xc0221640 <ehci_hub_control+824>: sub r7, r3, #1 ; 0x1
>> 0xc0221644 <ehci_hub_control+828>: add r3, r11, #16 ; 0x10
>> 0xc0221648 <ehci_hub_control+832>: add r3, r8, r3, lsl #2
>> 0xc022164c <ehci_hub_control+836>: uxth r7, r7
>> 0xc0221650 <ehci_hub_control+840>: ldrb r5, [r3, #5]
>> 0xc0221654 <ehci_hub_control+844>: ldrb r2, [r3, #4]
>> 0xc0221658 <ehci_hub_control+848>: orr r5, r2, r5, lsl #8
>> 0xc022165c <ehci_hub_control+852>: ldrb r2, [r3, #6]
>> 0xc0221660 <ehci_hub_control+856>: ldrb r3, [r3, #7]
>> 0xc0221664 <ehci_hub_control+860>: orr r5, r5, r2, lsl #16
>> 0xc0221668 <ehci_hub_control+864>: orr r5, r5, r3, lsl #24
>> 0xc022166c <ehci_hub_control+868>: dmb sy
>>
>> As you can see, the old compiler accesses the ehci status register
>> in a single access, the new compiler dances around and makes multiple
>> accesses, which in the end get very incorrect data (I think that this
>> register is like many which clear bits on reads).
>>
>> Any ideas where I can go with this? I'm really trying to keep up with
>> Poky/Yocto, but this move to GCC 4.6.0 has broken my ARM targets :-(
>> I do have PowerPC targets as well - they seem fine (from limited testing)
>> with the new compiler.
>>
>> Note: if you want to see the whole function disassembly, look at
>> http://www.mlbassoc.com/poky/ehci_hub_control-disassembly-gcc-4.5.2
>> http://www.mlbassoc.com/poky/ehci_hub_control-disassembly-gcc-4.6.0
>>
>> Thanks
>>
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-- 
Darren Hart
Intel Open Source Technology Center
Yocto Project - Linux Kernel