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Mon, 06 Apr 2020 04:59:18 -0700 (PDT) X-Gm-Message-State: AGi0PuZ4/vkj/vsXu0eVlrN5FrKfl2LF84F5QDpuyzeHp2vyswSQsK3A jxs+UVIm7yl7m8bmaPKwSYenkIrDKnTMKXPkk9o= X-Google-Smtp-Source: APiQypJz0OEtYujbR7iine9xuBKkfeyqVPQ+jUYZluuEMFR3kYewPuo9cQnrkW3MDy1Ob3mb/SNfyjoQ8u1U3xEBTgs= X-Received: by 2002:a05:6602:1550:: with SMTP id h16mr18761797iow.171.1586174358002; Mon, 06 Apr 2020 04:59:18 -0700 (PDT) MIME-Version: 1.0 References: <20200404073047.17898-1-ardb@kernel.org> <20200406110401.GA4650@red-moon.cambridge.arm.com> <20200406113235.GB4650@red-moon.cambridge.arm.com> In-Reply-To: <20200406113235.GB4650@red-moon.cambridge.arm.com> From: Ard Biesheuvel Date: Mon, 6 Apr 2020 13:59:07 +0200 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] arm64: iort: take _DMA methods into account for named components To: Lorenzo Pieralisi X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200406_045919_055276_97D41788 X-CRM114-Status: GOOD ( 21.34 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Catalin Marinas , Will Deacon , robin.murphy@arm.com, Linux ARM Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, 6 Apr 2020 at 13:32, Lorenzo Pieralisi wrote: > > On Mon, Apr 06, 2020 at 01:16:15PM +0200, Ard Biesheuvel wrote: > > On Mon, 6 Apr 2020 at 13:04, Lorenzo Pieralisi > > wrote: > > > > > > On Sat, Apr 04, 2020 at 09:30:47AM +0200, Ard Biesheuvel wrote: > > > > Where IORT nodes for named components can describe simple DMA limits > > > > expressed as the number of address bits a device can driver, _DMA methods > > > > in AML can express more complex topologies, involving DMA translation in > > > > particular. > > > > > > > > Currently, we only take this _DMA method into account if it appears on a > > > > ACPI device node describing a PCIe root complex, but it is perfectly > > > > acceptable to attach them to named components as well, so let's ensure > > > > we take them into account in those cases too. > > > > > > ACPI spec v6.3, 6.2.4 _DMA: > > > > > > "_DMA is only defined under devices that represent buses" > > > > > > > Sure. But ACPI0004 module devices are also bus nodes, so that > > statement does not exclude named components that are defined under > > such a module device. > > Yes. _DMA is valid only if a _CRS is present, ACPI0004 does not seem > to _require_ a _CRS to be considered valid. > How is that relevant? Any node that has a _DMA must have a _CRS as well. Some nodes that don't have a _DMA may not have a _CRS either. But that does not disqualify a ACPI0004 that *does* have both from being considered a bus node, no? Or is that not what you are saying? > It is an example. Better to make the _DMA definition more robust > and linked to ACPI0004, for instance. > If there is wording in the spec that says that only APCI0004 or PNP0A03/PNP0A08 should be considered to be bus nodes, then we should probably do that. But I wonder if that is really the intent, and whether vendors could denote bus nodes using their own HID namespace instead. > > > This should probably be updated and _DMA usage clarified - we can't > > > leave it open to interpretation. > > > > > > > Clarification is always better. > > Yes, we should be able to get this in as an Errata, better to be clear > given that it is something that will be used extensively across > platforms. > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel