From mboxrd@z Thu Jan 1 00:00:00 1970 From: Al Stone Subject: Re: [PATCH 09/12] ACPI: add clarifying comment about processor throttling in HW reduced mode Date: Thu, 21 Nov 2013 16:11:07 -0700 Message-ID: <528E930B.4000206@linaro.org> References: <1384047382-20623-1-git-send-email-al.stone@linaro.org> <4621090.bSNFRSzQnY@vostro.rjw.lan> <528D2F98.6050601@linaro.org> <4444379.hCFxGeZRVi@vostro.rjw.lan> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-ie0-f177.google.com ([209.85.223.177]:43693 "EHLO mail-ie0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754658Ab3KUXLK (ORCPT ); Thu, 21 Nov 2013 18:11:10 -0500 Received: by mail-ie0-f177.google.com with SMTP id tp5so817072ieb.8 for ; Thu, 21 Nov 2013 15:11:09 -0800 (PST) In-Reply-To: <4444379.hCFxGeZRVi@vostro.rjw.lan> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: "Rafael J. Wysocki" Cc: linux-acpi@vger.kernel.org, linaro-acpi@lists.linaro.org, Al Stone On 11/20/2013 05:14 PM, Rafael J. Wysocki wrote: > On Wednesday, November 20, 2013 02:54:32 PM Al Stone wrote: >> On 11/17/2013 03:20 PM, Rafael J. Wysocki wrote: >>> On Saturday, November 09, 2013 06:36:19 PM al.stone@linaro.org wrote: >>>> From: Al Stone >>>> >>>> Signed-off-by: Al Stone >>>> --- >>>> drivers/acpi/processor_throttling.c | 8 ++++++++ >>>> 1 file changed, 8 insertions(+) >>>> >>>> diff --git a/drivers/acpi/processor_throttling.c b/drivers/acpi/processor_throttling.c >>>> index e7dd2c1..200738e 100644 >>>> --- a/drivers/acpi/processor_throttling.c >>>> +++ b/drivers/acpi/processor_throttling.c >>>> @@ -942,6 +942,10 @@ static int acpi_processor_get_fadt_info(struct acpi_processor *pr) >>>> return -EINVAL; >>>> } >>>> >>>> + /* >>>> + * NB: in HW reduced mode, duty_width is always zero >>>> + * so this count may not be what is wanted. >>>> + */ >>>> pr->throttling.state_count = 1 << acpi_gbl_FADT.duty_width; >>>> >>>> /* >>>> @@ -991,6 +995,10 @@ static int acpi_processor_set_throttling_fadt(struct acpi_processor *pr, >>>> /* Used to clear all duty_value bits */ >>>> duty_mask = pr->throttling.state_count - 1; >>>> >>>> + /* >>>> + * NB: in HW reduced mode, duty_offset is always zero >>>> + * so this mask may not be what is wanted. >>>> + */ >>>> duty_mask <<= acpi_gbl_FADT.duty_offset; >>>> duty_mask = ~duty_mask; >>>> } >>> >>> I'm not sure how these comments help to be honest. It looks like >>> pr->throttling.state_count should be 0 in HW reduced mode, shouldn't it? >>> >> >> It should. The comments clarified things for me but perhaps >> they should just note that these values are always zero in >> reduced HW mode. The other option would be to not add any >> comments, of course. Hopefully someone working with reduced >> HW mode would be aware of these changes to the FADT values. >> >> I can go either way; what's the preference? > > I would just avoid making changes until we figure out what to do ultimately > here. That depends on what pr->throttling.state_count is used for and that > part should be hardened against pr->throttling.state_count == 0. Having > done that, we can simply set pr->throttling.state_count = 0 in the HW reduced > mode without adding any comments at all. > > Thanks! > I'll remove this patch for now. I think what makes sense is a separate patch to harden the use of pr->throttling.state_count in processor_throttling.c and processor_thermal.c. I see a couple of places where the values may not make sense when it is zero (regardless of reduced HW mode) but I think I'd like to treat that as a separate issue and think it through some more. -- ciao, al ----------------------------------- Al Stone Software Engineer Linaro Enterprise Group al.stone@linaro.org -----------------------------------