From: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
To: Arnd Bergmann <arnd@arndb.de>, <linux-arm-kernel@lists.infradead.org>
Cc: <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>
Subject: Re: [PATCH 2/2] ACPI / scan: Parse _CCA and setup device coherency
Date: Wed, 29 Apr 2015 09:45:43 -0500 [thread overview]
Message-ID: <5540EE97.70202@amd.com> (raw)
In-Reply-To: <5542288.z0SSOZ4xV7@wuerfel>
On 04/29/2015 09:03 AM, Arnd Bergmann wrote:
> 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
>
Actually, I am trying to implement the logic for when missing _CCA to be
consistent with the behavior when the devicetree entry does not specify
"dma-coherent" property. IIUC, in such case, Linux will default to using
non-coherent DMA.
Thanks,
Suravee
next prev parent reply other threads:[~2015-04-29 14:46 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-29 13:44 [PATCH 0/2] ACPI : Introduce support for _CCA object Suravee Suthikulpanit
2015-04-29 13:44 ` [PATCH 1/2] arm/arm64: ACPI: Introduce CONFIG_ACPI_MUST_HAVE_CCA Suravee Suthikulpanit
2015-04-29 14:04 ` Catalin Marinas
2015-04-29 14:31 ` Suravee Suthikulpanit
2015-04-29 14:42 ` Catalin Marinas
2015-04-29 14:44 ` Suravee Suthikulpanit
2015-04-30 13:47 ` Hanjun Guo
2015-04-30 13:50 ` Will Deacon
2015-04-30 14:14 ` Hanjun Guo
2015-04-30 15:01 ` Lorenzo Pieralisi
2015-04-29 13:44 ` [PATCH 2/2] ACPI / scan: Parse _CCA and setup device coherency Suravee Suthikulpanit
2015-04-29 14:03 ` Arnd Bergmann
2015-04-29 14:45 ` Suravee Suthikulpanit [this message]
2015-04-29 14:47 ` [Linaro-acpi] " Arnd Bergmann
2015-04-29 14:57 ` Suthikulpanit, Suravee
2015-04-29 15:39 ` Al Stone
2015-04-29 16:15 ` Arnd Bergmann
2015-04-29 15:54 ` Arnd Bergmann
2015-05-01 11:06 ` Catalin Marinas
2015-05-08 14:08 ` Arnd Bergmann
2015-05-11 17:10 ` Catalin Marinas
2015-05-11 17:24 ` Robin Murphy
2015-04-29 16:25 ` Arnd Bergmann
2015-04-29 21:53 ` Suravee Suthikulpanit
2015-04-30 8:23 ` [Linaro-acpi] " Arnd Bergmann
2015-04-30 10:41 ` Will Deacon
2015-04-30 10:47 ` Arnd Bergmann
2015-04-30 11:07 ` Will Deacon
2015-04-30 11:24 ` Arnd Bergmann
2015-04-30 11:46 ` Will Deacon
2015-04-30 13:03 ` Arnd Bergmann
2015-04-30 13:13 ` Will Deacon
2015-04-30 13:52 ` Arnd Bergmann
2015-04-30 15:55 ` Catalin Marinas
2015-05-08 14:01 ` Arnd Bergmann
2015-04-30 23:39 ` Suravee Suthikulanit
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