From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp-out3.simply.com (smtp-out3.simply.com [94.231.106.210]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2410B7E76B; Thu, 7 Mar 2024 12:42:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=94.231.106.210 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709815344; cv=none; b=i/kdBIgnqEHt3yldHBBNmcgPltRrwRbEjqZxM83IwCW23ikOFHrq/q8cr2f9AqpOJicOUGCfkeueV/8ZLQ5HE+xhyWlXLXXmMho/y08IJqyEGFjkMf7qUd36iv33MZWMDX8ey5nURq/iQx9x5DAPKGZgsFLANwpii5AMNZpgvZI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709815344; c=relaxed/simple; bh=t6HuFttPC1nxD+nyrrov2Y2NoChjRlY3Abi30iwUEyA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=G1Wz96tUieUlgavuoOsXGycrxt1f/q+87S8X1QXld1hdA69FhTei9QfMxg331sBg993JAcg/73zegonD5L73k36ndejscnnNbXRj0fkkYuZDhGz1p060ggOFlwQIopOMg2Z3gCGf5fgmvM99yTG0dERaWIzx5MSHPH3PvtEdyMQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=gaisler.com; spf=pass smtp.mailfrom=gaisler.com; dkim=pass (1024-bit key) header.d=gaisler.com header.i=@gaisler.com header.b=EdsQNeU6; arc=none smtp.client-ip=94.231.106.210 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=gaisler.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gaisler.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=gaisler.com header.i=@gaisler.com header.b="EdsQNeU6" Received: from localhost (localhost [127.0.0.1]) by smtp.simply.com (Simply.com) with ESMTP id 4Tr88819Wpz686f; Thu, 7 Mar 2024 13:42:16 +0100 (CET) Received: from [192.168.0.25] (h-98-128-223-123.NA.cust.bahnhof.se [98.128.223.123]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client did not present a certificate) by smtp.simply.com (Simply.com) with ESMTPSA id 4Tr87z50BGz6821; Thu, 7 Mar 2024 13:42:06 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gaisler.com; s=unoeuro; t=1709815335; bh=AVHNr47rSvulz8LrB0QQznO8Zw2QTzCYetLSkLBWuf4=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=EdsQNeU616Fl0FTZl709rzR8Xv5Qe21y99dZvo+Xe5uc50GnmuOwMEEulTzrVUMQJ NvD9sACX5r2g2QNQ5g7PLCkrSYzBTcIe/JhIaNGEx9Gd/WdWUg2UkBJI+cJAGY2qnl VjaWLmRBcT+SpQVQdcGoKb8OaDg7P1GCNjsi9aEg= Message-ID: <74afd65d-85ed-4ee9-b5f2-a6702f9bc01c@gaisler.com> Date: Thu, 7 Mar 2024 13:42:06 +0100 Precedence: bulk X-Mailing-List: sparclinux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 4/7] sparc32: Do not select ZONE_DMA Content-Language: en-US To: Arnd Bergmann , Sam Ravnborg , "Maciej W. Rozycki" , sparclinux@vger.kernel.org, Randy Dunlap Cc: Miquel Raynal , linux-parport@lists.infradead.org, "David S . Miller" , linux-kernel@vger.kernel.org References: <20240224-sam-fix-sparc32-all-builds-v2-0-1f186603c5c4@ravnborg.org> <20240224-sam-fix-sparc32-all-builds-v2-4-1f186603c5c4@ravnborg.org> <8d5780f5-1047-48d7-a9c9-09b95c7b5604@gaisler.com> <5648dca0-4853-4dfb-91cf-282a656beb1e@app.fastmail.com> <75a4a08d-85c2-4a60-9cbd-90dd50f765a8@app.fastmail.com> <5d97d50a-9d40-4651-8071-073dee5f9aa8@gaisler.com> <001ba36a-9d4c-45c4-b1f2-448824848afc@app.fastmail.com> <5568f26d-9e1a-4530-a086-564659b21666@app.fastmail.com> From: Andreas Larsson In-Reply-To: <5568f26d-9e1a-4530-a086-564659b21666@app.fastmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 2024-03-06 19:19, Arnd Bergmann wrote: > On Wed, Mar 6, 2024, at 17:22, Arnd Bergmann wrote: >> On Wed, Mar 6, 2024, at 16:31, Andreas Larsson wrote: > >> On a relate note, it does seem odd to have such a small >> lowmem area, and I wonder if that could be extended. >> The 192MB lowmem limit comes from >> >> #define SRMMU_MAXMEM 0x0c000000 >> >> but I don't understand if that is a hardware limitation >> or a design choice that can be changed, and if it is >> even valid on leon or only on the old sun machines. > > I had another look and found that this is a result of > > arch/sparc/include/asm/page_32.h:#define PAGE_OFFSET 0xf0000000 > > which gives 3840MiB to userspace addresses, leaving only > 256MiB for kernel lowmem and vmalloc space, which is > less than any other architectures. > > I still don't know the history behind this choice, but I > see this was already configured the same when arch/sparc/ > was originally merged. You can probably change it to a more > sensible 0xc0000000 or 0x80000000 like on other > architectures and run without highmem on anything with > less than 2GB of total RAM. > > How much RAM do Leon machines have typically, or at the > maximum? The amount of RAM can vary greatly between systems, from less that 128 MiB up to 2 GiB. An upcoming design uses the entire 36-bit physical address space and have the possibility of having up to 60 GiB memory. Thanks, Andreas