From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sudeep Holla Subject: Re: [PATCH v7 8/8] PCC: Enable PCC only when needed Date: Tue, 21 Jul 2015 16:28:43 +0100 Message-ID: <55AE652B.7030409@arm.com> References: <55AD042D.9040204@arm.com> <4609299.WWrJ4WHTsa@vostro.rjw.lan> <55AE0F7B.8010804@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from foss.arm.com ([217.140.101.70]:60503 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932618AbbGUP2r (ORCPT ); Tue, 21 Jul 2015 11:28:47 -0400 In-Reply-To: Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: "Rafael J. Wysocki" Cc: Sudeep Holla , "Rafael J. Wysocki" , Ashwin Chaugule , "jaswinder.singh@linaro.org" , "linux-pm@vger.kernel.org" , "linux-acpi@vger.kernel.org" , "linaro-acpi@lists.linaro.org" , "patches@linaro.org" , "viresh.kumar@linaro.org" Hi Rafael, On 21/07/15 15:34, Rafael J. Wysocki wrote: > Hi Sudeep, > > On Tue, Jul 21, 2015 at 11:23 AM, Sudeep Holla wrote: >> >> >> On 20/07/15 23:04, Rafael J. Wysocki wrote: >>> >>> On Monday, July 20, 2015 03:22:37 PM Sudeep Holla wrote: >>>> >>>> >>>> On 09/07/15 19:04, Ashwin Chaugule wrote: >>>>> >>>>> CPPC is the first client to make use of the PCC Mailbox channel. So >>>>> enable it only when CPPC is also enabled. >>>>> >>>> This sounds like a reverse dependency to me. So if there's some client >>>> unrelated to CPPC using PCC, CPPC_LIB needs to be selected to enable PCC >>>> ? >>> >>> >>> No. The other client will need to select PCC too. >> >> >> Yes the PCC users/clients selecting PCC is fine and that's already >> done(i.e. ACPI_CPPC_LIB selects PCC). I still don't understand the need >> for this change, also how will other clients possibly select PCC which >> now depends on CPPC_LIB ? e.g. if we have >> >> config ACPI_XYZ_LIB >> select PCC >> >> config ACPI_XYZ >> select ACPI_XYZ_LIB >> >> Won't this shout warning: (ACPI_XYZ_LIB && ACPI_CPPC_LIB) selects PCC >> which has unmet direct dependencies (MAILBOX && ACPI && ACPI_CPPC_LIB) >> if ACPI_CPPC_LIB is not selected ? > > That depends on the "depends on" clauses used. Selecting itself > doesn't cause any dependencies to appear. > Agreed and I am absolutely fine with that. But if you look at this patch, it does config PCC bool "Platform Communication Channel Driver" depends on ACPI && ACPI_CPPC_LIB I am fine with ACPI_CPPC_LIB selecting PCC which is already done in earlier patch. I am against making PCC depend on ACPI_CPPC_LIB. Lets assume it's fine to do that. Now if another feature XYZ as in my example say on x86 selects PCC then you will *get warnings* as we will not able to select PCC without selecting ACPI_CPPC_LIB after this patch and x86 will never select ACPI_CPPC_LIB. I did test something like my XYZ example and it did trigger the warning as I suspected. I am sorry either I am missing to understand again or unable to express the problem here :( >> OK, for now we enable ACPI_CPPC_LIB on ARM64 and not on x86. When x86 >> has a PCC client how will that select PCC without ACPI_CPPC_LIB. Sorry >> if I am missing to understand something. > > Presumably, the new feature will have a Kconfig option associated with > it and it will do "select PCC" too. > As I say I am fine with that and no arguments there. Regards, Sudeep