linux-kernel - Re: [PATCH 3/3] intel_pstate: add module and kernel command line parameter to ignore ACPI

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Message-ID: <20141120132317.00ad7210@kcaccard-desk.amr.corp.intel.com>
Date:	Thu, 20 Nov 2014 13:23:17 -0800
From:	Kristen Carlson Accardi <kristen@...ux.intel.com>
To:	ethan <ethan.kernel@...il.com>
Cc:	Ethan Zhao <ethan.zhao@...cle.com>,
	"<dirk.j.brandewie@...el.com>" <dirk.j.brandewie@...el.com>,
	"<viresh.kumar@...aro.org>" <viresh.kumar@...aro.org>,
	"<rjw@...ysocki.net>" <rjw@...ysocki.net>,
	"<corbet@....net>" <corbet@....net>,
	"<linux-doc@...r.kernel.org>" <linux-doc@...r.kernel.org>,
	"<linux-kernel@...r.kernel.org>" <linux-kernel@...r.kernel.org>,
	"<linux-pm@...r.kernel.org>" <linux-pm@...r.kernel.org>,
	"<joe.jin@...cle.com>" <joe.jin@...cle.com>,
	"<brian.maly@...cle.com>" <brian.maly@...cle.com>
Subject: Re: [PATCH 3/3] intel_pstate: add module and kernel command line
 parameter to ignore ACPI _PPC

On Thu, 20 Nov 2014 08:57:34 +0800
ethan <ethan.kernel@...il.com> wrote:

> 
> 
> > 在 2014年11月20日，03:05，Kristen Carlson Accardi <kristen@...ux.intel.com> 写道：
> > 
> > On Tue, 18 Nov 2014 17:37:06 +0900
> > Ethan Zhao <ethan.zhao@...cle.com> wrote:
> > 
> >> Add kernel command line parameter
> >> intel_pstate = ignore_acpi_ppc
> >> and module parameter
> >> ignore_acpi_ppc = 1
> >> to allow driver to ignore the ACPI _PPC existence even for Sun x86 servers.
> >> These parameter could be used for debug\test\workaround etc purpose.
> >> 
> >> Signed-off-by: Ethan Zhao <ethan.zhao@...cle.com>
> > 
> > What if we used a more generic parameter like "force" that would bypass
> > any vendor specific checks and just load anyway?  This way we don't have
> > to add new parameters everything some new thing shows up that we want to
> > ignore.
> > 
> To be honest, I prefer more generic parameter. But to avoid the possible negative affect 
> To another vendors. I back to this way.

Well, your parameter can still impact other vendors as it is.  it
is pretty typical to assume that using a parameter like "force" means
you know what you are doing and accept the risks.  Especially if its
documented as such.

> 
> Thanks,
> Ethan
> >> ---
> >> Documentation/kernel-parameters.txt | 3 +++
> >> drivers/cpufreq/intel_pstate.c      | 8 +++++++-
> >> 2 files changed, 10 insertions(+), 1 deletion(-)
> >> 
> >> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> >> index 4c81a86..f502b85 100644
> >> --- a/Documentation/kernel-parameters.txt
> >> +++ b/Documentation/kernel-parameters.txt
> >> @@ -1446,6 +1446,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
> >>               disable
> >>                 Do not enable intel_pstate as the default
> >>                 scaling driver for the supported processors
> >> +               ignore_acpi_ppc
> >> +             Ignore the existence of ACPI method _PPC for Sun x86 servers
> >> +             and load the driver.
> >> 
> >>    intremap=    [X86-64, Intel-IOMMU]
> >>            on    enable Interrupt Remapping (default)
> >> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> >> index 7c5faea..388387b 100644
> >> --- a/drivers/cpufreq/intel_pstate.c
> >> +++ b/drivers/cpufreq/intel_pstate.c
> >> @@ -870,6 +870,7 @@ static struct cpufreq_driver intel_pstate_driver = {
> >> };
> >> 
> >> static int __initdata no_load;
> >> +static unsigned int  ignore_acpi_ppc;
> >> 
> >> static int intel_pstate_msrs_not_valid(void)
> >> {
> >> @@ -990,7 +991,7 @@ static bool intel_pstate_platform_pwr_mgmt_exists(void)
> >>            intel_pstate_no_acpi_pss())
> >>            return true;
> >>        if (!strncmp(hdr.oem_id, v_info->oem_id, ACPI_OEM_ID_SIZE) &&
> >> -            intel_pstate_has_acpi_ppc())
> >> +            intel_pstate_has_acpi_ppc() && !ignore_acpi_ppc)
> >>            return true;
> >>    }
> >> 
> >> @@ -1066,11 +1067,16 @@ static int __init intel_pstate_setup(char *str)
> >> 
> >>    if (!strcmp(str, "disable"))
> >>        no_load = 1;
> >> +    if (!strcmp(str, "ignore_acpi_ppc"))
> >> +        ignore_acpi_ppc = 1;
> >>    return 0;
> >> }
> >> early_param("intel_pstate", intel_pstate_setup);
> >> #endif
> >> 
> >> +module_param(ignore_acpi_ppc, uint, 0644);
> >> +MODULE_PARM_DESC(ignore_acpi_ppc,
> >> +    "value 0 or non-zero. non-zero -> ignore ACPI _PPC and load this driver");
> >> MODULE_AUTHOR("Dirk Brandewie <dirk.j.brandewie@...el.com>");
> >> MODULE_DESCRIPTION("'intel_pstate' - P state driver Intel Core processors");
> >> MODULE_LICENSE("GPL");
> > 

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