From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robert Johnson Subject: PowerPC PPC32 CONFIG_HIGHMEM dependency question Date: Mon, 17 Mar 2014 17:41:25 +0000 Message-ID: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT To: "linux-rt-users@vger.kernel.org" Return-path: Received: from 66-162-147-187.static.twtelecom.net ([66.162.147.187]:51135 "EHLO spibarracuda01.sierraphotonics.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1757101AbaCQRlM convert rfc822-to-8bit (ORCPT ); Mon, 17 Mar 2014 13:41:12 -0400 Received: from SPIEXCHMAIL01.sierraphotonics.com ([192.168.10.45]) by spibarracuda01.sierraphotonics.com with ESMTP id Cy8J333o005Tecy9 for ; Mon, 17 Mar 2014 10:41:11 -0700 (PDT) Content-Language: en-US Sender: linux-rt-users-owner@vger.kernel.org List-ID: I am using an embedded single board computer (SBC) that has a Freescale P2020 processor. The vendor board support package (BSP) for this product currently uses a 3.0.4 Linux kernel. In looking through the RT patch for various Linux kernel versions even up through 3.12.13-rt21, I see that CONFIG_HIGHMEM is not allowed if CONFIG_PREEMPT_RT_FULL is selected (see arch/powerpc/Kconfig). The result for my SBC is that if I enable CONFIG_PREEMPT_RT_FULL in the kernel, I am then only able to access 1GB of RAM instead of the 4GB that is resident. Is there any way to get CONFIG_PREEMPT_RT_FULL to work with CONFIG_HIGHMEM? If I want to use CONFIG_HIGHMEM, should I consider the use of CONFIG_PREEMPT_RTB which does not appear to have a dependency?