From mboxrd@z Thu Jan 1 00:00:00 1970 From: Shuah Khan Subject: RE: [PATCH v4 0/6] ACPI: Add _OST support for ACPI hotplug Date: Tue, 29 May 2012 16:44:56 -0600 Message-ID: <1338331496.2722.18.camel@lorien2> References: <1337826324-16802-1-git-send-email-toshi.kani@hp.com> <1337880880.2718.68.camel@lorien2> <1337888931.16730.393.camel@misato.fc.hp.com> <94F2FBAB4432B54E8AACC7DFDE6C92E346ACC639@ORSMSX101.amr.corp.intel.com> Reply-To: shuahkhan@gmail.com Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: Received: from g1t0029.austin.hp.com ([15.216.28.36]:15400 "EHLO g1t0029.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752176Ab2E2Wo6 (ORCPT ); Tue, 29 May 2012 18:44:58 -0400 In-Reply-To: <94F2FBAB4432B54E8AACC7DFDE6C92E346ACC639@ORSMSX101.amr.corp.intel.com> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: "Moore, Robert" Cc: shuahkhan@gmail.com, Toshi Kani , "lenb@kernel.org" , "linux-acpi@vger.kernel.org" , "bhelgaas@google.com" , "liuj97@gmail.com" , "andi@firstfloor.org" , "linux-kernel@vger.kernel.org" On Tue, 2012-05-29 at 22:27 +0000, Moore, Robert wrote: > > > 2. Calling acpi_get_handle() on _OST prior to executing the method. > > > This will ensure that this method only gets run if it is present > > under > > > the device in question. Coupled with what is already outlined in #1 > > > above, now _OST gets executed only when it is defined under the > > device object. > > > Example case in the existing code, please see > > acpi_processor_ppc_ost() > > > implementation. > > > > Yes, I did look at acpi_processor_ppc_ost() when I implemented the > > function. I believe calling acpi_get_handle() is redundant since > > acpi_ns_get_node() is called within acpi_evaluate_object() as well. > > acpi_evaluate_object() simply returns with AE_NOT_FOUND when _OST > > method does not exist. > > > > This is correct. If _OST does not exist, AE_NOT_FOUND will be returned from evaluate_object. Yes that is correct from the ACPI Spec and implementation point of view. My thinking is that a call to acpi_get_handle() might not penalize the OS as much as acpi_evaluate_object() would on systems that don't actually implement _OST. In other words, acpi_get_handle() might not go as deep as acpi_evaluate_object() would go into the ACPI layer, hence might be a safer measure on platforms that don't actually implement this optional method under all devices included in this patch set. -- Shuah