Quoting Viresh Kumar (2015-10-08 00:48:28) > On 07-10-15, 21:12, Arnd Bergmann wrote: > > I think it clearly makes sense to have a fixed length for each of these > > members: > > > > either 32 bit is enough to represent all possible values, then > > there is no need to make them 'long' on 64-bit architectures, or 32 bit > > is not enough and then the code is broken on 32-bit architectures today > > and should be fixed. > > I agree. > > But I am not 100% sure why it was done this way to start with. > Probably this is the logic behind that: > - Max clock rate supported by a u32 is ~ 4.295 GHz > - People expected that, we will not reach this rate for 32 bit systems > but for 64 bit ones. > - If above is true, then making it u64 for all will generate not very > optimized code for 32bit systems, as we need to fetch two 32bit > values everytime then. > - And making it u32 for 64 bit systems wouldn't be great as well, as > we need to mask out half of the read value. > > Ofcourse, Mike and Stephen can correct me here :)
I chose unsigned long for the common clock framework _implemenation_, because the long-standing clk.h _api_ returns this type for clk_get_rate and passes this type in for clk_set_rate and clk_round_rate. > > > In my patch, I assumed that if 32-bit architectures work fine today, then > > we don't need more range on 64-bit architectures either. > > The problem here is that we haven't fixed it properly. > - clock framework expects it to be unsigned long > - DT is sending a 64 bit value in Hz > - But we are storing and exposing it in u32 Don't forget cpufreq is using unsigned int for KHz. > > That's weird, isn't it? Yes it is. > > So, either we update clock API and other similar APIs to u64 or u32 > (which may not be the right thing to do), Or we keep it unsigned long > here as well and add debugfs_create_ulong(). This comes up every now and then. I'm still trying to figure out if sub-Hertz quantities should be considered (e.g. representing freqs in milliHertz). Regards, Mike > > -- > viresh -- 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/
