From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <3B7034A0.C55D871F@snmc.com> Date: Tue, 07 Aug 2001 11:34:09 -0700 From: Daris A Nevil MIME-Version: 1.0 To: Tom Roberts Cc: "Justin (Gus) Hurwitz" , linuxppc-embedded@lists.linuxppc.org Subject: Re: Non-cacheable memory References: <3B70104B.C1E6F8EC@lucent.com> Content-Type: text/plain; charset=us-ascii Sender: owner-linuxppc-embedded@lists.linuxppc.org List-Id: Gus, Tom, Here is the procedure I used to allocate pages and mark them as non-cached in the 2.2.5 kernel (SNMC's QSLinux): mem_addr = __get_free_page(GFP_KERNEL); pte = va_to_pe(&init_task, mem_addr); pte_val(*pte) |= _PAGE_NO_CACHE; flush_tlb_page(current->mm_mmap, mem_addr); I used these pages for SCC buffer descriptors, so they were never returned to the system. I'm not sure if this is the preferred way, but it certainly works. I have not tried this in the 2.4 kernel yet. The functions __get_free_page() and flush_tlb_page() do exist in 2.4.4, but I could not locate va_to_pe() (I think that was a macro in 2.2.5). You may also want to look at the file linux/asm/pgalloc.h, esp. the functions get_pgd_slow() and get_pgd_fast(). Regards, Daris Nevil Tom Roberts wrote: > "Justin (Gus) Hurwitz" wrote: > > Does the current 2_4_devel tree have support for allocating regions of > > non-cachable memory? And, if so, what is the proper (or preferred) way of > > doing this? > > What I did in 2.2.15 was to edit the main startup routine to call my driver > directly so it could "eat up" a region of memory before Linux started its > memory management. I then used a BAT to reference it uncached. Yes, this > is ugly, and requires care in making sure the BAT effective address is > otherwise unused by the kernel, but it works. This is on a MPC7400, and > other PowerPC CPUs might not have BATs available.... -- Daris A Nevil Simple Network Magic Corporation 401 Kentucky Lane McKinney, TX 75069 214-793-7757 dnevil@snmc.com www.snmc.com quickstack.com qslinux.org ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/