From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (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 9C43C70 for ; Mon, 7 Jun 2021 06:19:22 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id BD91467373; Mon, 7 Jun 2021 08:19:18 +0200 (CEST) Date: Mon, 7 Jun 2021 08:19:18 +0200 From: Christoph Hellwig To: Nick Kossifidis Cc: guoren@kernel.org, anup.patel@wdc.com, palmerdabbelt@google.com, arnd@arndb.de, wens@csie.org, maxime@cerno.tech, drew@beagleboard.org, liush@allwinnertech.com, lazyparser@gmail.com, wefu@redhat.com, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-sunxi@lists.linux.dev, Guo Ren , Christoph Hellwig Subject: Re: [RFC PATCH v2 06/11] riscv: pgtable: Add DMA_COHERENT with custom PTE attributes Message-ID: <20210607061918.GA24060@lst.de> References: <1622970249-50770-1-git-send-email-guoren@kernel.org> <1622970249-50770-10-git-send-email-guoren@kernel.org> <610849b6f66e8d5a9653c9f62f46c48d@mailhost.ics.forth.gr> X-Mailing-List: linux-sunxi@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <610849b6f66e8d5a9653c9f62f46c48d@mailhost.ics.forth.gr> User-Agent: Mutt/1.5.17 (2007-11-01) On Sun, Jun 06, 2021 at 08:22:14PM +0300, Nick Kossifidis wrote: > This patch violates the Privilege Spec section 4.4.1 that clearly states: > > "Bits63–54 are reserved for future standard use and must be zeroed by > software for forward compatibility" > > Standard use means that valid values can only be defined by the Priv. Spec, > not by the vendor (otherwise they'd be marked as "custom use" or "platform > use"), and since they "must" be zeroed by software we 'll be violating the > Privilege Spec if we do otherwise. Yes, that is why I think it is a no-go.