From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lithops.sigma-star.at (mailout.nod.at [116.203.167.152]) (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 07B042D839F; Wed, 10 Sep 2025 19:37:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=116.203.167.152 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757533063; cv=none; b=G5PHlblLW/36WGMXbZ7ChXNm0tfkzQ/YZAHm/maY+o696RMgzGFgHxfEgJ6jvidxnyGfZmi3NB38qP554d90iOK5CQItJo/0atGoxYPsjzrfYR6WLIUIpsijiN1gxdhzBCBb8YL0DuiydOOyAfBhFeLzPxOxjeZPxtxMirERQEU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757533063; c=relaxed/simple; bh=Kvy79l38OjgXam56LG4SBUALLkxIDxyLLpk0bImYB5k=; h=Date:From:To:Cc:Message-ID:In-Reply-To:References:Subject: MIME-Version:Content-Type; b=ZQGKD8iMEiGgiIw5Z0Cepw+3ucV0RujC1KjQPqfnmk4lngmZ7rb8e9i6JJmYxPxaglM7r5zgOHMEHNyzYLqAaBAAtX+kS4W3Uhux42PhhOeIBQ1qY89bkBnwq9dBECP0K0GlmkAHo1yA6RXkCJu2YtJ2/VPsdu1WTcuJKT7uTaU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=nod.at; spf=fail smtp.mailfrom=nod.at; arc=none smtp.client-ip=116.203.167.152 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=nod.at Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=nod.at Received: from localhost (localhost [127.0.0.1]) by lithops.sigma-star.at (Postfix) with ESMTP id E33972C14AA; Wed, 10 Sep 2025 21:37:38 +0200 (CEST) Received: from lithops.sigma-star.at ([127.0.0.1]) by localhost (lithops.sigma-star.at [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id mZ4QcxbfF_Ic; Wed, 10 Sep 2025 21:37:38 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by lithops.sigma-star.at (Postfix) with ESMTP id 274732BA98D; Wed, 10 Sep 2025 21:37:38 +0200 (CEST) Received: from lithops.sigma-star.at ([127.0.0.1]) by localhost (lithops.sigma-star.at [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id Q1j44iMB0ybE; Wed, 10 Sep 2025 21:37:38 +0200 (CEST) Received: from lithops.sigma-star.at (lithops.sigma-star.at [195.201.40.130]) by lithops.sigma-star.at (Postfix) with ESMTP id D9D02CE340; Wed, 10 Sep 2025 21:37:37 +0200 (CEST) Date: Wed, 10 Sep 2025 21:37:37 +0200 (CEST) From: Richard Weinberger To: Christophe Leroy Cc: Arnd Bergmann , ksummit , linux-kernel , linux-arm-kernel , linuxppc-dev , linux-mips , linux-mm , imx , Lucas Stach , Linus Walleij , Geert Uytterhoeven , Ankur Arora , David Hildenbrand , Mike Rapoport , Lorenzo Stoakes , Matthew Wilcox , Andrew Morton , "Liam R. Howlett" , vbabka , Suren Baghdasaryan , Ira Weiny , Nishanth Menon , heiko , Alexander Sverdlin , "Chester A. Unal" , Sergio Paracuellos , Andreas Larsson Message-ID: <1586788245.22320.1757533057730.JavaMail.zimbra@nod.at> In-Reply-To: References: <4ff89b72-03ff-4447-9d21-dd6a5fe1550f@app.fastmail.com> <497308537.21756.1757513073548.JavaMail.zimbra@nod.at> Subject: Re: [TECH TOPIC] Reaching consensus on CONFIG_HIGHMEM phaseout Precedence: bulk X-Mailing-List: imx@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Mailer: Zimbra 8.8.12_GA_3807 (ZimbraWebClient - FF141 (Linux)/8.8.12_GA_3809) Thread-Topic: Reaching consensus on CONFIG_HIGHMEM phaseout Thread-Index: BY4xIXfJeETYMNF0Cnq/68k1mYFqTg== Christophe, ----- Urspr=C3=BCngliche Mail ----- > Von: "Christophe Leroy" > Can you tell which PPC32 model/family you are using ? Is it mpc85xx or > and/or other variants ? Maybe we can look at keeping CONFIG_HIGHMEM or > find alternatives for that subset of PPC32 only. Off the head, MPC8343 and QorIQ P1022. >=20 > Could you also elaborate a bit on the kind of issues you forsee or fear > with applications and FPGA device drivers. Unfortunately, applications in this area often make certain assumptions about the amount or layout of memory. This becomes a bigger problem when using FPGA device drivers of questionable quality, which share memory between the kernel, userspace, and the device itself. These are mostly out-of-tree drivers, so that's my horse to ride,=20 I'm just mentally preparing myself for "interesting" bugs that will need to be sorted out. > FWIW I sent out today a patch that removes CONFIG_HIGHMEM complely on > powerpc in order to get a better view of the impacted areas and allow > people to test what it looks like on their system without > CONFIG_HIGHMEM. See [1]. Oh, that was fast. :-) Thanks, //richard