From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peng Fan Subject: Re: [RFC V2] xen: interface: introduce pvclk interface Date: Wed, 20 Jan 2016 21:52:34 +0800 Message-ID: <20160120135232.GA10911@linux-7smt.suse> References: <1453278682-8750-1-git-send-email-van.freenix@gmail.com> <1453292827.26343.98.camel@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: Received: from mail6.bemta14.messagelabs.com ([193.109.254.103]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1aLtCD-0003Wd-EM for xen-devel@lists.xenproject.org; Wed, 20 Jan 2016 13:53:13 +0000 Received: by mail-pf0-f177.google.com with SMTP id q63so5334998pfb.1 for ; Wed, 20 Jan 2016 05:53:11 -0800 (PST) Content-Disposition: inline In-Reply-To: <1453292827.26343.98.camel@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Ian Campbell Cc: Stefano Stabellini , George Dunlap , Julien Grall , David Vrabel , xen-devel@lists.xenproject.org List-Id: xen-devel@lists.xenproject.org Hi Ian, Stefano On Wed, Jan 20, 2016 at 12:27:07PM +0000, Ian Campbell wrote: >On Wed, 2016-01-20 at 12:06 +0000, Stefano Stabellini wrote: >> On Wed, 20 Jan 2016, Peng Fan wrote: >> > To my use case, Dom0 and DomU both use device tree, I need to build >> > the mapping table between id and name, since I use name to lookup >> > the clk in backend, like this: >> > "clk =3D __clk_loopkup(clkname); clk_prepare_enable(clk)". Maybe ACPI >> > is another different case. >> = >> Theoretically on systems using ACPI there is no need to fiddle with >> clocks, > >I mentioned ACPI in my replies to v1 more as a placeholder for "other >firmware descriptions than DT", in order that the pv protocol we end up >with does not end up being DT specific, which would be a mistake >irrespective of what may or may not be required for non-DT firmware >descriptions. Thanks for clarifying. Beside this, are you ok with the xenstore node descr= iption in this file? Thanks, Peng. > >Ian. > >> see >> = >> Documentation/arm64/arm-acpi.txt >> = >> = >> "In DT, clocks need to be specified >> and the drivers need to take them into account.=A0=A0In ACPI, the assump= tion >> is that UEFI will leave the device in a reasonable default state, >> including >> any clock settings.=A0=A0If for some reason the driver needs to change a >> clock >> value, this can be done in an ACPI method; all the driver needs to do is >> invoke the method and not concern itself with what the method needs to do >> to change the clock.=A0=A0Changing the hardware can then take place over= time >> by changing what the ACPI method does, and not the driver. >> = >> In DT, the parameters needed by the driver to set up clocks as in the >> example >> above are known as "bindings"; in ACPI, these are known as "Device >> Properties" >> and provided to a driver via the _DSD object." >> = >> = >> However currently we don't have the ability to run ACPI in DomU guests >> on ARM. Even if we had, there is no way to call native ACPI methods from >> any guests other than Dom0, even on x86. We just have to hope that >> clocks don't need to be reset on ACPI systems.