From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mark Rutland Subject: Re: [PATCH 19/19] Documentation: ACPI for ARM64 Date: Tue, 29 Jul 2014 12:28:24 +0100 Message-ID: <20140729112824.GM2576@leverpostej> References: <1406206825-15590-1-git-send-email-hanjun.guo@linaro.org> <1406206825-15590-20-git-send-email-hanjun.guo@linaro.org> <20140728100654.GC24078@leverpostej> <20140728164459.GD32359@quad.lixom.net> <20140729102940.GB18250@cbox> <20140729105543.GL2576@leverpostej> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: Content-Disposition: inline In-Reply-To: <20140729105543.GL2576@leverpostej> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Christoffer Dall Cc: Mark Brown , Catalin Marinas , Will Deacon , Lv Zheng , "rob.herring@linaro.org" , Lorenzo Pieralisi , Daniel Lezcano , Robert Moore , "linux-acpi@vger.kernel.org" , "grant.likely@linaro.org" , Charles Garcia-Tobin , Robert Richter , Jason Cooper , Arnd Bergmann , Marc Zyngier , Liviu Dudau , Bjorn Helgaas , "linux-arm-kernel@lists.infradead.org" , "graeme.gregory@linaro.org" , Randy Dunlap , Rafael J List-Id: linux-acpi@vger.kernel.org T24gVHVlLCBKdWwgMjksIDIwMTQgYXQgMTE6NTU6NDNBTSArMDEwMCwgTWFyayBSdXRsYW5kIHdy b3RlOgo+IE9uIFR1ZSwgSnVsIDI5LCAyMDE0IGF0IDExOjI5OjQwQU0gKzAxMDAsIENocmlzdG9m ZmVyIERhbGwgd3JvdGU6Cj4gPiBPbiBNb24sIEp1bCAyOCwgMjAxNCBhdCAwOTo0NDo1OUFNIC0w NzAwLCBPbG9mIEpvaGFuc3NvbiB3cm90ZToKPiA+ID4gT24gTW9uLCBKdWwgMjgsIDIwMTQgYXQg MTE6MDY6NTRBTSArMDEwMCwgTWFyayBSdXRsYW5kIHdyb3RlOgo+ID4gCj4gPiBbLi4uXQo+ID4g Cj4gPiA+ID4gPgo+ID4gPiA+ID4gPiArUmVsYXRpb25zaGlwIHdpdGggRGV2aWNlIFRyZWUKPiA+ ID4gPiA+ID4gKy0tLS0tLS0tLS0tLS0tLS0tLS0tLS0tLS0tLS0tCj4gPiA+ID4gPiA+ICsKPiA+ ID4gPiA+ID4gK0FDUEkgc3VwcG9ydCBpbiBkcml2ZXJzIGFuZCBzdWJzeXN0ZW1zIGZvciBBUk12 OCBzaG91bGQgbmV2ZXIgYmUgbXV0dWFsbHkKPiA+ID4gPiA+ID4gK2V4Y2x1c2l2ZSB3aXRoIERU 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X19fX19fX19fX19fX19fXwpsaW51eC1hcm0ta2VybmVsIG1haWxpbmcgbGlzdApsaW51eC1hcm0t a2VybmVsQGxpc3RzLmluZnJhZGVhZC5vcmcKaHR0cDovL2xpc3RzLmluZnJhZGVhZC5vcmcvbWFp bG1hbi9saXN0aW5mby9saW51eC1hcm0ta2VybmVsCg== From mboxrd@z Thu Jan 1 00:00:00 1970 From: mark.rutland@arm.com (Mark Rutland) Date: Tue, 29 Jul 2014 12:28:24 +0100 Subject: [PATCH 19/19] Documentation: ACPI for ARM64 In-Reply-To: <20140729105543.GL2576@leverpostej> References: <1406206825-15590-1-git-send-email-hanjun.guo@linaro.org> <1406206825-15590-20-git-send-email-hanjun.guo@linaro.org> <20140728100654.GC24078@leverpostej> <20140728164459.GD32359@quad.lixom.net> <20140729102940.GB18250@cbox> <20140729105543.GL2576@leverpostej> Message-ID: <20140729112824.GM2576@leverpostej> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tue, Jul 29, 2014 at 11:55:43AM +0100, Mark Rutland wrote: > On Tue, Jul 29, 2014 at 11:29:40AM +0100, Christoffer Dall wrote: > > On Mon, Jul 28, 2014 at 09:44:59AM -0700, Olof Johansson wrote: > > > On Mon, Jul 28, 2014 at 11:06:54AM +0100, Mark Rutland wrote: > > > > [...] > > > > > > > > > > > > > +Relationship with Device Tree > > > > > > +----------------------------- > > > > > > + > > > > > > +ACPI support in drivers and subsystems for ARMv8 should never be mutually > > > > > > +exclusive with DT support at compile time. > > > > > > + > > > > > > +At boot time the kernel will only use one description method depending on > > > > > > +parameters passed from the bootloader. > > > > > > > > > > Possibly overriden by kernel bootargs. And as debated for quite a > > > > > while earlier this year, acpi should still default to off -- if a DT > > > > > and ACPI are both passed in, DT should at this time be given priority. > > > > > > > > Why? I really don't see the logic in doing that. > > > > > > Seems like I am replying to your emails in reverse order. > > > > > > > Currently the kernel can only boot using DT, so DT will be used even if > > > > ACPI is present. In the presence of ACPI support in the kernel, ACPI > > > > would be used on said systems. > > > > > > For all the reasons we hashed out earlier this year: We can't trust that > > > vendors will know how to do ACPI from day one, so instead of loading up the > > > kernel with lots of quirks and workarounds, we'll default to not using it until > > > we're at a point where things look mature enough. > > > > > > The alternative is to keep this patch set out of the kernel. We can do that > > > too, but I don't think that really helps anyone. > > > > > > > From the discussions at the last Linaro Connect, this was seen as > > > > important for virtual machines which want to provide ACPI services to > > > > guests while still being able to boot DT-only kernels. I'll leave it to > > > > Grant, Rob, and Christoffer to cover that. > > > > > > Ok, waiting to see what they have to say then. > > > > > > > Hmm, a virtual machine implementaion may provide either a DT or ACPI (or > > both). I think the point at Linaro Connect was that for a first cut, > > there is no obvious need to provide ACPI to VMs and to be spec > > compliant, server kernels must be able to boot with DT-only. In most > > cases such systems will only access a few limited emulated devices > > (UART, GIC, RTC, flash controller) and VirtIO devices, which should just > > work using DT only. > > > > People are talking about adding ACPI for VM guests as well for various > > reasons (device passthrough for example) in which case I would always > > expect people to run UEFI inside their guests too (perhaps this is not > > 100% true in the case of Xen fast-boot scenarios though) and I would > > expect Linux to only see the little stub DT and ACPI. > > > > Does this clarify anything or add futher to the confusion? > > I was under the impression that there was a case where we'd have a DT > with HW description in a VM which also had ACPI tables, to enable a > kernel without ACPI support to boot in said VM (albeit with reduced > functionality). > > I may have got confused since the VM standards discussion at LCA-14. I took a look at the video [1,2] of said session [3], and it looks like I was the one arguing for the case of full description in both DT and ACPI, so either I was confused or I've forgotten some hallway discussion. I think my reasoning was somewhat flawed; if the hypervisor defaults to providing DT, with an option to use ACPI in certain cases (where not all guests would be expected to work), then that would cover the "grab an iso, it just works?" use case for Linux images while allowing for the cases where people want ACPI in the VM. The only issue with that would be catering for OSs which support ACPI but not DT or whose DT support is not Linux-compatible. Thanks, Mark. [1] http://www.youtube.com/watch?v=Qh3SX3p3B74 [2] http://people.linaro.org/linaro-connect/lca14/videos/03-03-Monday/LCA14-101-%20ARM%20VM%20Standards.mp4 [3] http://lca-14.zerista.com/event/member/102395