On Thu, Jun 9, 2016 at 5:09 AM, Sudeep Holla <[email protected]> wrote: > > > On 08/06/16 20:31, Jon Mason wrote: >> >> On Wed, Jun 08, 2016 at 09:34:06AM +0100, Sudeep Holla wrote: >>> >>> >>> >>> On 07/06/16 22:08, Jon Mason wrote: >>>> >>>> Query the CPU core clock in the device tree to determine the core clock >>>> speed. >>> >>> >>> How do guarantee that it's the current frequency of the CPU ? >> >> >> I am basing it on the assumption (perhaps incorrect) that the clock in >> the CPU DT corresponds to the one determining the CPU clock rate. And, >> that this clock rate is accurate in describing the speed at which the >> CPU is currently running. >> > > As you already noticed, it's not always correct. > > [..] > >>> >>> What if they just don't have in DT but have DVFS support ? >> >> >> This can be extended to cover DVFS or SMC calls or anything else. >> This was simply a first step to cover what appeared to be the most >> prevalent case. >> > > Using DVFS/CPUFreq makes this DT based approach irrelevant. > >>> Also whey do we need this support when the user-space can query the >>> CPUFreq sysfs which is more accurate and maintains the current running >>> frequency ? >> >> >> This is exactly what x86 is doing to provide its value in >> /proc/cpuinfo. I could easily augment this patch to call >> cpufreq_quick_get(), if it returns 0, then call clk_get_rate(). If >> both return 0, then simply not print out anything (which would cover >> all of the possibilities). Or, I could have it just call >> cpufreq_quick_get() to get the value. >> > > Agree x86 has, may be for legacy reasons. It even has CPUFreq sysfs > entries which is architecture agnostic while /proc/cpuinfo is more > architecture based. So applications that want to be portable across > architectures must choose the generic CPUFreq sysfs path rather than > some x86 based cpuinfo.
Thank you for educating me. I am taking this (and RMK's comment) as any modification to add CPU speed to /proc/cpuinfo is not welcomed, anyone who wants to query this should instead look at cpufreq in sysfs, and any dev who wants to add such a thing should look into writing a driver in drivers/cpufreq/. Thanks, Jon > > -- > Regards, > Sudeep
