>Subject: Re: [PATCH 1/2] powerpc/85xx: fix problem that prevents >PHYS_64BIT from configurable > > >On Feb 16, 2012, at 6:10 AM, Li Yang wrote: > >> Fix the problem that large physical address support cannot be disabled >> when some platforms which only provides 36-bit support are selected. >> According to the philosophy of kernel config enabling a platform >> support doesn't mean the kernel is only running on that platform. >> Remove the auto selection of PHYS_64BIT option for these platforms. >> They will need to use a 36bit default config that selects PHYS_64BIT >> explicitly. >> >> The reason why we need to keep PHYS_64BIT option configurable is that >> enabling it cause negative performance impact on various aspects like >> TLB miss and physical address manipulating. We should not enable it >> unless really needed, e.g. use large memory of 4GB or bigger. >> >> Signed-off-by: Li Yang <le...@freescale.com> >> --- >> arch/powerpc/platforms/85xx/Kconfig | 6 ------ >> 1 files changed, 0 insertions(+), 6 deletions(-) > >Nak, this isn't correct. > >For some of these platforms like P2041RDB, P3041DS, P3060QDS, P4080DS, & >P5020DS only a 36-bit physical address map is supported by u-boot and the >device tree. This was a decision that was made to NOT support 32-bit >address map for these boards and accept the performance implication of it >to reduce the # of builds, etc.
Ok. Although personally I don't think # of builds matters that much. > >Additionally, outside of maybe P2041RDB I believe the majority of these >boards ship with 4G of DDR (but that off the top of my head) and thus >require the 36-bit / PHYS_64BIT support to be enabled. I know that current support of DPAA boards requires 36-bit. But I don't think they need to select the PHYS_64BIT option directly and make it not configurable. It's conflicting with the logic that enabling a platform support doesn't mean the kernel is only running on that platform. Btw: what's your recommendations on solving this? - Leo _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
