From: "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@amd.com>
To: Arnd Bergmann <arnd@arndb.de>,
"linaro-acpi@lists.linaro.org" <linaro-acpi@lists.linaro.org>
Cc: "linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"catalin.marinas@arm.com" <catalin.marinas@arm.com>,
"rjw@rjwysocki.net" <rjw@rjwysocki.net>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"will.deacon@arm.com" <will.deacon@arm.com>,
"linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
"lenb@kernel.org" <lenb@kernel.org>,
"Charles Garcia-Tobin" <Charles.Garcia-Tobin@arm.com>
Subject: Re: [Linaro-acpi] [PATCH 2/2] ACPI / scan: Parse _CCA and setup device coherency
Date: Wed, 29 Apr 2015 14:57:10 +0000 [thread overview]
Message-ID: <D1665A4F.19E17%suravee.suthikulpanit@amd.com> (raw)
In-Reply-To: <3246744.xVj4sLRlWl@wuerfel>
On 4/29/15, 09:47, "Arnd Bergmann" <arnd@arndb.de> wrote:
>On Wednesday 29 April 2015 09:45:43 Suravee Suthikulpanit wrote:
>> 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.
>
>Why?
>
> Arnd
Otherwise, it would seem inconsistent with what states in the ACPI spec:
CCA objects are only relevant for devices that can access CPU-visible
memory,
such as devices that are DMA capable. On ARM based systems, the _CCA
object
must be supplied all such devices. On Intel platforms, if the _CCA
object is
not supplied, the OSPM will assume the devices are hardware cache
coherent.
>From the statement above, I interpreted as if it is not present, it would
be non-coherent.
Suravee
next prev parent reply other threads:[~2015-04-29 14:57 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
2015-04-29 14:47 ` [Linaro-acpi] " Arnd Bergmann
2015-04-29 14:57 ` Suthikulpanit, Suravee [this message]
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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