linux-kernel - Re: [PATCH v5] printk: Add pr_info_show

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Message-ID: <68db835b-4053-4785-f385-9a455bc505e2@android.com>
Date:   Mon, 24 Jul 2017 08:47:38 -0700
From:   Mark Salyzyn <salyzyn@...roid.com>
To:     Pavel Machek <pavel@....cz>
Cc:     linux-kernel@...r.kernel.org, andriy.shevchenko@...ux.intel.com,
        joe@...ches.com, prarit@...hat.com, rjw@...ysocki.net,
        tglx@...utronix.de, Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Kees Cook <keescook@...omium.org>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Mark Salyzyn <salyzyn@...gle.com>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Olof Johansson <olof@...om.net>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH v5] printk: Add pr_info_show_time

On 07/22/2017 02:40 AM, Pavel Machek wrote:
>> For example, the persistent clock that is used to report
>> "Suspended for" message, although very useful, is not present on all
>> platforms.  It is currently standardized for millisecond precision.
> Fix that on your platforms, instead?
>
> 								Pavel

lol :-)

That is a _hardware_ issue. For a vast majority of them, the persistent 
read-only clock requires a LTE, always-on ready to wakeup device for a 
phone call, correction factor from a separate driver. In some cases the 
persistent clock requires a hardware re-init sequence to a pmic 
controller that occurs higher up in the resume chain. For those where it 
is possible, please remember there are 25K different Android devices, 
represented in nearly 2B hands. Feel free to tell all the implementors 
just how important a continuously accessible working 100% tuned accurate 
persistent clock is when _this_ _one_ flawed (ms accuracy, no lte 
correction while asleep) print is the only place which gains from said 
access ;-). I am blue in the face just working with the limited set I 
have influence on.

And yet, add a simple print of realtime clock at suspend and resume 
points higher up in the chain always works regardless of the hardware or 
the driver skills of the vendor building the devices.

-- Mark