From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 31A581007D3 for ; Fri, 17 Feb 2012 12:27:46 +1100 (EST) Subject: Re: [PATCH 1/2] powerpc/85xx: fix problem that prevents PHYS_64BIT from configurable Mime-Version: 1.0 (Apple Message framework v1257) Content-Type: text/plain; charset=us-ascii From: Kumar Gala In-Reply-To: <1329394210-1014-1-git-send-email-leoli@freescale.com> Date: Thu, 16 Feb 2012 19:27:41 -0600 Message-Id: References: <1329394210-1014-1-git-send-email-leoli@freescale.com> To: Li Yang Cc: linuxppc-dev@ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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. >=20 > 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. >=20 > Signed-off-by: Li Yang > --- > 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. 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. - k