Am 01.01.2011 20:21, schrieb Dirk Behme:
On 01.01.2011 19:47, Alexander Holler wrote:
Am 01.01.2011 19:25, schrieb Dirk Behme:
On 01.01.2011 18:52, Alexander Holler wrote:
Hello,
Am 01.01.2011 13:04, schrieb Dirk Behme:
On 22.12.2010 12:04, Alexander Holler wrote:
gcc 4.5.1 seems to ignore (at least some) volatile definitions, avoid that as done in the kernel.
Reading C99 6.7.3 8 and the comment 114) there, I think it is a bug of that gcc version to ignore the volatile type qualifier used e.g. in __arch_getl(). Anyway, using a definition as in the kernel headers avoids such optimizations when gcc 4.5.1 is used.
Maybe the headers as used in the current linux-kernel should be used, but to avoid large changes, I've just added a small change to the current headers.
Do you like to test the patch in the attachment? I named it 'v4'.
After some thinking and testing, it seems to me that the volatile optimization issue this patch shall fix is only with the readx() macros. So the idea is to drop all writex() changes done in the v3 version of this patch. With dropping the writex() changes, we would drop all issues we discussed with e.g. the GCC statement-expression and the do while workaround, too.
I've come across a bug which reads as the problem might be fixed in gcc 4.5.2:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45052
I will test gcc 4.5.2 in the next days.
Have you been able to test v4 of the patch I sent with gcc 4.5.1?
No, sorry, I don't have a test case for consequent write* and I will have to write one.
?
If I remember correctly, the test case for this patch was compiling U-Boot with 4.5.1 and then check
a) if it boots at Beagle (correct clock.c) b) if NAND works ok (correct omap_gpmc.c)
?
No. None of those must fail when the compiler optimizes consequent write* to one write* because the compiler ignores the volatile keyword. I've only found the problem with consequent read* (in clock.c), but there might be problems with consequent write* somewhere else too. So if you remove the change for those write* some other problems might arise and just through booting a kernel those might not be found. So I think it would be dangerous to remove the change for write* when using gcc 4.5.x
And because the patch fixes only write* and read* some stuff in u-boot which uses volatile in another context might still fail, therefore I vote to use the current kernel headers where other things besides read* and write* are using those barriers too.
Regards,
Alexander