On 06/29/2010 10:38 PM, Daniel Walker wrote:
On Tue, 2010-06-29 at 21:03 +0200, Martijn Stolk wrote:
No worries. I wanted to isolate what specifically fixes the problem
myself in order to make a minimal patch. I'm also hoping for some help
regarding information, as I don't have access to official QSD8250
documentation.
I've found the key register that differs between between how it is
initialized for Windows CE and for Linux, and solves the problem for us.
It is the Auxilliary Control Register (cp15, 0, c1, c0, 1).
For Windows CE it is initialized to 0x002C0077
(=0b00000000001011000000000001110111)
For Linux it is initialized to 0x000C0037
(=0b00000000000011000000000000110111)
The following page explains this register for the Cortex-A8, the ARM
core on which the QSD8250 is based:
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0344k/Bgbffjhh.html
The 7th bit (bit 6 on that page) controls the behaviour of the
Invalidate All& by MVA instructions. It needs to be disabled for Linux.
The 22nd bit, however, is in an area marked as "reserved" on that page.
I am very curious what this bit does. Maybe this reserved area is
documented in QSD8250 documentation? Could anyone provide clearity about
this bit?
You found that you needed both of these set? One or the other wasn't
enough.
I'm not sure that we can open talk about what this 22nd bit does, so I'd
just set it like you have it and not worry about it.
Daniel
Here's a table on what I noticed during my tests:
bit: 7 | 22 | remark
1 | 1 | Linux crashes due to segmentation faults
0 | 1 | Linux works fine, no crashes, no segfaults
0 | 0 | Same as above
1 | 0 | Linux doesn't segfault immediately, but seems to only
cause problems
when the device is idling for a second or less (maybe
power management
or something).
Disabling bit 7 solves the segfault issues already. Bit 22 just causes
some mysterious behaviour which I am curious about. We're able to
continue without knowing this of course, but I was hoping you were
allowed to answer a specific question like this. Don't worry if you can't.
Thanks either way for your help.
Regards,
Martijn
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