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On POWERNV platform, the fields for pstates in the Power Management Status Register (PMSR) and the Power Management Control Register (PMCR) are 8-bits wide. On POWER8 the pstates are negatively numbered while on POWER9 they are positively numbered. The device-tree exports pstates as 32-bit entries. The device-tree implementation sign-extends the 8-bit pstate values to obtain the corresponding 32-bit entry. Eg: On POWER8, a pstate value 0x82 [-126] is represented in the device-tree as 0xfffffff82 while on POWER9, the same value 0x82 [130] is represented in the device-tree as 0x00000082. The powernv-cpufreq driver implementation represents pstates using the integer type. In multiple places in the driver, the code interprets the pstates extracted from the PMSR as a signed byte and assigns it to a integer variable to get the sign-extention. On POWER9 platforms which have greater than 128 pstates, this results in the driver performing incorrect sign-extention, and thereby treating a legitimate pstate (say 130) as an invalid pstates (since it is interpreted as -126). This patch fixes the issue by implementing a helper function to extract Pstates from PMSR register, and correctly sign-extend it to be consistent with the values provided by the device-tree. Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com> Acked-by: Balbir Singh <bsingharora@gmail.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.