linux-kernel - Re: [PATCH 1/2] PM: base: power: don't try to use non-existing RTC for storing data

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Date:   Mon, 6 Sep 2021 19:07:37 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Juergen Gross <jgross@...e.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        xen-devel@...ts.xenproject.org,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Stable <stable@...r.kernel.org>
Subject: Re: [PATCH 1/2] PM: base: power: don't try to use non-existing RTC
 for storing data

On Fri, Sep 3, 2021 at 11:02 AM Juergen Gross <jgross@...e.com> wrote:
>
> On 03.09.21 10:56, Greg Kroah-Hartman wrote:
> > On Fri, Sep 03, 2021 at 10:49:36AM +0200, Juergen Gross wrote:
> >> In there is no legacy RTC device, don't try to use it for storing trace
> >> data across suspend/resume.
> >>
> >> Cc: <stable@...r.kernel.org>
> >> Signed-off-by: Juergen Gross <jgross@...e.com>
> >> ---
> >>   drivers/base/power/trace.c | 10 ++++++++++
> >>   1 file changed, 10 insertions(+)
> >>
> >> diff --git a/drivers/base/power/trace.c b/drivers/base/power/trace.c
> >> index a97f33d0c59f..b7c80849455c 100644
> >> --- a/drivers/base/power/trace.c
> >> +++ b/drivers/base/power/trace.c
> >> @@ -13,6 +13,7 @@
> >>   #include <linux/export.h>
> >>   #include <linux/rtc.h>
> >>   #include <linux/suspend.h>
> >> +#include <linux/init.h>
> >>
> >>   #include <linux/mc146818rtc.h>
> >>
> >> @@ -165,6 +166,9 @@ void generate_pm_trace(const void *tracedata, unsigned int user)
> >>      const char *file = *(const char **)(tracedata + 2);
> >>      unsigned int user_hash_value, file_hash_value;
> >>
> >> +    if (!x86_platform.legacy.rtc)
> >> +            return 0;
> >
> > Why does the driver core code here care about a platform/arch-specific
> > thing at all?  Did you just break all other arches?
>
> This file is only compiled for x86. It depends on CONFIG_PM_TRACE_RTC,
> which has a "depends on X86" attribute.

This feature uses the CMOS RTC memory to store data, so if that memory
is not present, it's better to avoid using it.

Please feel free to add

Reviewed-by: Rafael J. Wysocki <rafael@...nel.org>

to this patch or let me know if you want me to take it.