>-----Original Message----- >From: Bjorn Helgaas [mailto:bjorn.helgaas@xxxxxx] >Sent: Wednesday, October 25, 2006 4:21 PM >To: Pallipadi, Venkatesh >Cc: linux-acpi@xxxxxxxxxxxxxxx; linux-ia64@xxxxxxxxxxxxxxx >Subject: Re: ia64 acpi-cpufreq driver > >On Monday 23 October 2006 22:46, Pallipadi, Venkatesh wrote: >> >Section 8.4.4.1 (_PCT) of the 3.0 ACPI spec says: >> > >> > OSPM performs processor performance transitions by writing >> > the performance state-specific control value to a Performance >> > Control Register (PERF_CTRL). >> > >> >According to one of our architecture guys, this means we really >> >ought to have an OpRegion driver that encapsulates the >PAL_SET_PSTATE >> >call. >> >> Actually it is slightly different from low_level_read and write. >> Generic ACPI definition of ACPI PERF_CTRL and PERF_STATUS define >> them as if they are registers. But, with FfixedHW, ACPI allows >> architectures to implement this functionality in a native way. > >I'd like to understand this better. Something like the following >patch (not for inclusion, may not even compile) is what I'm >thinking. This seems more in line with the spec intent. > >Apart from details like "bit_width <= 8" vs. "bit_width == 8", >this should be functionally the same. Are you saying it's different >because of those details, or is there a larger difference I don't >understand? > Yes. Something like this will work. I don't think it is the intent of the SPEC. As I understand, FFH in SPEC is intended to be used whenever we have hardware/processor specific interfaces (As described in ACPI 3.0 spec - page 46). Also, it will complicate the code. I think having separate code, even if there is some amount of duplication is there, is better in this case. The reasons: - i386 acpi-cpufreq code has support for both IO port and FFH. Please refer to arch/i386/kernel/cpu/cpufreq/acpi-cpufreq.c in 2.6.19-rc2-mm2, which is a lot different from current git. - FFH in i386 works in a different way from IPF. Specifically, PERF_STATUS is just a register read, and hardware performance feedback is by using different APERF/MPERF MSR. But, in IPF it is done through passing a different type parameter to same PAL_GET_PSTATE calls (will be adding this to IPF driver soon). Thanks, Venki - To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
