linux-kernel - Re: [PATCH v7 00/17] Introduce ACPI for ARM64 based on ACPI 5.1

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Message-ID: <20150116152541.GG13634@e104818-lin.cambridge.arm.com>
Date:	Fri, 16 Jan 2015 15:25:41 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Will Deacon <Will.Deacon@....com>,
	Tom Lendacky <thomas.lendacky@....com>,
	Mark Rutland <Mark.Rutland@....com>,
	linaro-acpi <linaro-acpi@...ts.linaro.org>,
	Yijing Wang <wangyijing@...wei.com>,
	Rob Herring <robh@...nel.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Timur Tabi <timur@...eaurora.org>,
	ACPI Devel Mailing List <linux-acpi@...r.kernel.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Charles Garcia-Tobin <Charles.Garcia-Tobin@....com>,
	"phoenix.liyi@...wei.com" <phoenix.liyi@...wei.com>,
	Robert Richter <rric@...nel.org>,
	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <Marc.Zyngier@....com>,
	"jcm@...hat.com" <jcm@...hat.com>, Mark Brown <broonie@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"graeme.gregory@...aro.org" <graeme.gregory@...aro.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"hanjun.guo@...aro.org" <hanjun.guo@...aro.org>,
	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Olof Johansson <olof@...om.net>
Subject: Re: [PATCH v7 00/17] Introduce ACPI for ARM64 based on ACPI 5.1

On Fri, Jan 16, 2015 at 03:14:13PM +0000, Arnd Bergmann wrote:
> On Friday 16 January 2015 14:55:45 Will Deacon wrote:
> > On Fri, Jan 16, 2015 at 02:45:30PM +0000, Tom Lendacky wrote:
> > > I have tested ACPI-enablement patches for the amd-xgbe/amd-xgbe-phy
> > > drivers that I'm about to submit upstream with the V7 patch series
> > > on the AMD Seattle server platform. There does not appear to be support
> > > for the _CCA attribute in this patch series. The amd-xgbe driver will
> > > setup the device domain and cache attributes based on the presence of
> > > this attribute, but it requires the arch support to assign the proper
> > > DMA operations in order for it to all work correctly.
> > > 
> > > Overriding the _CCA attribute in the driver, I was able to successfully
> > > test the driver and this patch series.
> > 
> > Hopefully this will all be addressed when the IORT parts of ACPI have
> > settled down (the current proposal allows for these attributes to be
> > described as well as their interaction with things like IOMMUs).
> > 
> > In the meantime, are you falling back to non-coherent DMA? If so, what
> > attributes have you settled on? We need to be really careful not to
> > corrupt data during cache invalidatation when mapping a non-coherent
> > buffer for the CPU.
> 
> I think in case of ACPI we should use cache-coherent as the default,
> as this is what all servers will use for DMA masters.

Last time I heard in some call, it was agreed that _CCA properties
should always be present and Linux should not make any assumption (there
is no safe assumption here). While better options may appear in ACPI,
_CCA is what we currently have.

-- 
Catalin
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