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 _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
