From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dirk Behme Subject: Re: [PATCH v4] xen/arm: Add a clock property Date: Wed, 20 Jul 2016 14:53:44 +0200 Message-ID: <847d3d22-985d-cbe9-3cd9-7c85080fae37@de.bosch.com> References: <1468309605-19522-1-git-send-email-dirk.behme@de.bosch.com> <04d9dbfb-196d-a775-7fbb-526aba8085f4@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-clk-owner@vger.kernel.org To: Geert Uytterhoeven Cc: Julien Grall , "linux-arm-kernel@lists.infradead.org" , Mark Rutland , Michael Turquette , xen-devel@lists.xenproject.org, "devicetree@vger.kernel.org" , Stefano Stabellini , linux-clk , Stephen Boyd List-Id: devicetree@vger.kernel.org On 20.07.2016 14:46, Geert Uytterhoeven wrote: > Hi Julien, > > On Wed, Jul 20, 2016 at 2:10 PM, Julien Grall wrote: >> On 20/07/16 12:49, Geert Uytterhoeven wrote: >>> On Wed, Jul 20, 2016 at 1:01 PM, Julien Grall >>> wrote: >>>> On 20/07/16 10:43, Geert Uytterhoeven wrote: >>>>> On Tue, Jul 12, 2016 at 9:46 AM, Dirk Behme >>>>> wrote: >>>>>> Clocks described by this property are reserved for use by Xen, and the >>>>>> OS >>>>>> must not alter their state any way, such as disabling or gating a >>>>>> clock, >>>>>> or modifying its rate. Ensuring this may impose constraints on parent >>>>>> clocks or other resources used by the clock tree. >>>>>> >>>>>> This property is used to proxy clocks for devices Xen has taken >>>>>> ownership >>>>>> of, such as UARTs, for which the associated clock controller(s) remain >>>>>> under the control of Dom0. >>>>> >>>>> I'm not familiar with using XEN at all, but I'm a bit puzzled... >>>>> >>>>> Can't you just add a clocks property to the (virtual) serial device node >>>>> in DT? >>>>> Then the (virtual) serial device driver can get and enable the clock? >>>> >>>> There is no DT node for the Xen console (hvc). The UART used by Xen will >>>> be >>>> completely removed from the Device tree. >>> >>> Why is it removed? >> >> Because the device is used exclusively by Xen and DOM0 should not touch it >> at all (IRQs and MMIOs are not mapped). > > IMHO then it's Xen's responsability to make sure not to disable the clock(s). > > Who removes the device node from the DT? If Xen, can't it just remember > which clocks were present in removed device nodes? Yes, we are trying this with "moving" the clocks of the removed nodes to the Xen hypervisor node: https://lists.xen.org/archives/html/xen-devel/2016-06/msg02605.html The question discussed here is how to deal with these clocks properly in Linux, then. Best regards Dirk