On Fri, Jul 26, 2019 at 3:50 PM Park, Aiden <[email protected]> wrote: > > On Fri, Jul 26, 2019 at 10:00 AM Park, Aiden <[email protected]> wrote: > > > > > > Slim Bootloader already calibrated TSC and provides it to U-Boot. > > > Therefore, U-Boot does not have to re-calibrate TSC. > > > Configuring tsc_base and clock_rate makes x86 tsc_timer driver bypass > > > TSC calibration and use the provided TSC frequency. > > > - Get TSC frequency from performance info hob > > > - Set tsc_base and clock_rate for tsc_timer driver > > > > I'm still not convinced to have this. As kernel followed by U-Boot we thrust > > hardware more than something else. > > One more layer in between is usually an additional point to be error-prone. > > > > So, if something we may get directly from hardware, I consider better to > > get it > > from there. > > > > Of course, data structures can be left for sake of self-documentation. > > > Basically, Providing known information to a payload is Slim Bootloader > architecture concept. Slim Bootloader does initialize chipset and hardware > as much as it can, and provides useful information to a payload in HOBs > to minimize hardware re-initialization in a payload, make it generic > and make it light-weight. > > TSC frequency is specific to CPU or chipset, and the way to get exact TSC > frequency also varies depending on CPU. > ex) checking cpuid, platform info MSR, perf MSR for LFM/HFM/Turbo Mode, or > FSB. > All these consideration has already done in Slim Bootloader on each CPUs. > > I think that U-Boot tsc_timer also considers this case, and that's why > tsc_timer skips calibration in its probing time if tsc_base and clock_rate are > already configured. > > Kernel uses many timers like TSC, APIC timer, 8254 timer, HPET and so on. > I also understand kernel trusts hardware and re-calibrate them because all > these timers may not be properly configured in boot firmware stage. > But, HOB information including TSC must be trusted between Slim Bootloader > and its payload(U-Boot) in Slim Bootloader architecture.
Okay, I didn't remember if this is described in documentation. If it's not, please, add a section and put there somelike you expleined to me here. -- With Best Regards, Andy Shevchenko _______________________________________________ U-Boot mailing list [email protected] https://lists.denx.de/listinfo/u-boot
