Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
In-Reply-To: <20180524190031.GB31019@kroah.com>
References: <20180524175024.19874-1-robh@kernel.org> <20180524175024.19874-2-robh@kernel.org>
 <20180524190031.GB31019@kroah.com>
From:   Rob Herring <robh@kernel.org>
Date:   Thu, 24 May 2018 15:57:54 -0500
Message-ID: <CAL_JsqJK69A3W=YrSfvPetM95CROOJhU1bW1rMEOGtji=t0ORQ@mail.gmail.com>
Subject: Re: [PATCH v2 1/8] driver core: make deferring probe after init optional
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Linus Walleij <linus.walleij@linaro.org>,
        Alexander Graf <agraf@suse.de>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Kevin Hilman <khilman@kernel.org>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        Joerg Roedel <joro@8bytes.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Mark Brown <broonie@kernel.org>,
        Frank Rowand <frowand.list@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        devicetree@vger.kernel.org,
        Architecture Mailman List <boot-architecture@lists.linaro.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@lists.infradead.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, May 24, 2018 at 2:00 PM, Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
> On Thu, May 24, 2018 at 12:50:17PM -0500, Rob Herring wrote:
>> Deferred probe will currently wait forever on dependent devices to probe,
>> but sometimes a driver will never exist. It's also not always critical for
>> a driver to exist. Platforms can rely on default configuration from the
>> bootloader or reset defaults for things such as pinctrl and power domains.
>> This is often the case with initial platform support until various drivers
>> get enabled. There's at least 2 scenarios where deferred probe can render
>> a platform broken. Both involve using a DT which has more devices and
>> dependencies than the kernel supports. The 1st case is a driver may be
>> disabled in the kernel config. The 2nd case is the kernel version may
>> simply not have the dependent driver. This can happen if using a newer DT
>> (provided by firmware perhaps) with a stable kernel version.
>>
>> Subsystems or drivers may opt-in to this behavior by calling
>> driver_deferred_probe_check_init_done() instead of just returning
>> -EPROBE_DEFER. They may use additional information from DT or kernel's
>> config to decide whether to continue to defer probe or not.
>>
>> Cc: Alexander Graf <agraf@suse.de>
>> Signed-off-by: Rob Herring <robh@kernel.org>
>> ---
>>  drivers/base/dd.c      | 17 +++++++++++++++++
>>  include/linux/device.h |  2 ++
>>  2 files changed, 19 insertions(+)
>>
>> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
>> index c9f54089429b..d6034718da6f 100644
>> --- a/drivers/base/dd.c
>> +++ b/drivers/base/dd.c
>> @@ -226,6 +226,16 @@ void device_unblock_probing(void)
>>       driver_deferred_probe_trigger();
>>  }
>>
>> +int driver_deferred_probe_check_init_done(struct device *dev, bool optional)
>> +{
>> +     if (optional && initcalls_done) {
>
> Wait, what's the "optional" mess here?

My intent was that subsystems just always call this function and never
return EPROBE_DEFER themselves. Then the driver core can make
decisions as to what to do (such as the timeout added in the next
patch). Or it can print common error/debug messages. So optional is a
hint to allow subsystems per device control.

>
> The caller knows this value, so why do you need to even pass it in here?

Because regardless of the value, we always stop deferring when/if we
hit the timeout and the caller doesn't know about the timeout. If we
get rid of it, we'd need functions for both init done and for deferred
timeout.

> And bool values that are not obvious are horrid.  I had to go look this
> up when reading the later patches that just passed "true" in this
> variable as I had no idea what that meant.

Perhaps inverting it and calling it "keep_deferring" would be better.
However, the flag is ignored if we have timed out.

>
> So as-is, no, this isn't ok, sorry.
>
> And at the least, this needs some kerneldoc to explain it :)

That part is easy enough to fix.

Rob