On Wed, Dec 13, 2017 at 5:57 PM, Gautham R. Shenoy <e...@linux.vnet.ibm.com> wrote: > From: "Gautham R. Shenoy" <e...@linux.vnet.ibm.com> > > 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 <e...@linux.vnet.ibm.com> > ---
This looks better Acked-by: Balbir Singh <bsinghar...@gmail.com> Balbir Singh