On Wed, 30 Jan 2013, Russell King - ARM Linux wrote:
> On Wed, Jan 30, 2013 at 09:21:28AM +0100, walter harms wrote: > > Great hit Joe :) > > > > Sometimes i am really surprised what code can be found > > in the kernal and it is still working. > > Having no clue of the code i suspect somebody tries to > > check is mask outside the range it should read > > PHYS_OFFSET |( SZ_64M - 1) > > maybe someone should tell them that > > 1+1=10 while 1|1=1 > > It does not seem to matter here (or ... ?) > > This PCI host is only used on one platform (ARMCORE). > > For this, PHYS_OFFSET will be a value with only the top few bits of a > 32-bit word set (such as 0xc0000000) - it's certainly not going to have > any bits set below bit 26 on the platform this driver gets used on. > "SZ_64M - 1" is the size of the window that RAM appears. > > So, _either_ logical OR or addition works. > > If we _did_ end up with a PHYS_OFFSET with bits less than bit 26 set > here, we'd have bigger problems - because the base of RAM in PCI space > will not correspond with PHYS_OFFSET and all the DMA mapping stuff breaks. The "problem" is that the computation is done inconsistently within the same file. Sometimes with + and sometimes with |. julia -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
