From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH 2/2] ACPI / scan: Parse _CCA and setup device coherency Date: Wed, 29 Apr 2015 16:03:19 +0200 Message-ID: <5542288.z0SSOZ4xV7@wuerfel> References: <1430315049-4663-1-git-send-email-Suravee.Suthikulpanit@amd.com> <1430315049-4663-3-git-send-email-Suravee.Suthikulpanit@amd.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: In-Reply-To: <1430315049-4663-3-git-send-email-Suravee.Suthikulpanit@amd.com> Sender: linux-kernel-owner@vger.kernel.org To: linux-arm-kernel@lists.infradead.org Cc: Suravee Suthikulpanit , rjw@rjwysocki.net, lenb@kernel.org, catalin.marinas@arm.com, will.deacon@arm.com, al.stone@linaro.org, linaro-acpi@lists.linaro.org, linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, leo.duran@amd.com, hanjun.guo@linaro.org, msalter@redhat.com, grant.likely@linaro.org List-Id: linux-acpi@vger.kernel.org On Wednesday 29 April 2015 08:44:09 Suravee Suthikulpanit wrote: > + device->flags.cca_seen = 1; > + } else if (IS_ENABLED(CONFIG_ACPI_MUST_HAVE_CCA)) { > + /* > + * Architecture has specified that if the device > + * can do DMA, it must have ACPI _CCA object. > + * Here, there could be two cases: > + * 1. Not DMA-able device. > + * 2. DMA-able device, but missing _CCA object. > + * > + * In both cases, we will default to dma non-coherent. > + */ > + cca = 0; > + } else { > + /* > + * If architecture does not specify that device must > + * specify ACPI _CCA (e.g. x86), we default to use > + * dma coherent. > + */ > + cca = 1; > + } > What does it mean here if a device does DMA but is not coherent? Do you have an example of a server that needs this? Can we please make the default for ARM64 cca=1 as well? Arnd