[poky] BeagleBoard using GCC 4.6.0
Gary Thomas
gary at mlbassoc.com
Wed Jun 8 12:02:11 PDT 2011
On 06/08/2011 12:21 PM, Darren Hart 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).
>
> Gary,
>
> Thank you for digging into this. Excellent timing as I was looking at
> the same thing - I hadn't looked at the compiler yet as I was in the
> middle of some kernel work and had assumed the problem lay there. I'll
> see if I can try with the older kernel to get this resolved as well.
> Have you tried with various optimization options yet?
Not yet, I've only tried the basic options, etc, to try and see where
things might be going South.
>>
>> 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.
>>
>> 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
>>
>
--
------------------------------------------------------------
Gary Thomas | Consulting for the
MLB Associates | Embedded world
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