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Date:   Wed, 18 Oct 2023 09:56:14 +0200
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Subject: Re: [PATCH v1 1/1] Revert "pinctrl: avoid unsafe code pattern in
 find_pinctrl()"
To:     Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc:     Linus Walleij <linus.walleij@linaro.org>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        linux-gpio@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20231017141806.535191-1-andriy.shevchenko@linux.intel.com>
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From:   Ferry Toth <fntoth@gmail.com>
In-Reply-To: <ZS7_5VGvRnw99gzd@google.com>
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Hi,

(resend due to html reject)

On 17-10-2023 23:43, Dmitry Torokhov wrote:
> Hi Andy,
> 
> On Tue, Oct 17, 2023 at 10:45:39PM +0300, Andy Shevchenko wrote:
>> On Tue, Oct 17, 2023 at 08:59:05PM +0200, Linus Walleij wrote:
>>> On Tue, Oct 17, 2023 at 8:34 PM Andy Shevchenko
>>> <andriy.shevchenko@linux.intel.com> wrote:
>>>> On Tue, Oct 17, 2023 at 08:18:23PM +0200, Linus Walleij wrote:
>>>
>>>>> In the past some file system developers have told us (Ulf will know)
>>>>> that we can't rely on the block device enumeration to identify
>>>>> devices, and requires that we use things such as sysfs or the
>>>>> UUID volume label in ext4 to identify storage.
>>>>
>>>> While I technically might agree with you, this was working for everybody
>>>> since day 1 of support of Intel Merrifield added (circa v4.8), now _user
>>>> space_ is broken.
>>>
>>> Actually, I don't agree with that, just relaying it. I would prefer that we
>>> solve exactly the problem that we are facing here: some random unrelated
>>> code or similar affecting enumeration order of mmc devices.
> 
> Sorry, but the era of static configuration where one has a well defined
> order in which things are probed and numbered has long gone. The right
> answer is either device aliases that provides stable numbering on a
> board that is not dependent on scheduler behavior, mutexes
> implementation (how they deal with writer starvation, etc),
> kernel/driver/subsystem linking order and myriad other things, or
> mounting by UUID. The kernel does not provide any guarantees on the
> stability of device probe and instantiation order.
> 
> If you think about it it is the same issue as legacy GPIO numbering.
> It was convenient some time ago, but now it is no longer suitable or
> sufficient and could change when kernel is uprevved.
> 
>>>
>>> It's not the first time it happens to me, I have several devices that change
>>> this enumeration order depending on whether an SD card is plugged
>>> in or not, and in a *BIG* way: the boot partition on the soldered eMMC
>>> changes enumeration depending on whether an SD card is inserted
>>> or not, and that has never been fixed (because above).
>>
>> This is not the problem I have. I haven't added any SD card, hardware
>> configuration is the same. The solely difference in the whole setup is
>> this revert applied or not.
> 
> Yes, I guess there is a contention on this mutex and the fact that we
> are now taking it once and not twice makes difference in which probes
> happen. If you look at the logs, you will see that even before the patch
> controllers did not enumerate on the order of PCI functions:
> 
> [   36.439057] mmc0: SDHCI controller on PCI [0000:00:01.0] using ADMA
> [   36.450924] mmc2: SDHCI controller on PCI [0000:00:01.3] using ADMA
> [   36.459355] mmc1: SDHCI controller on PCI [0000:00:01.2] using ADMA

You are referring to the order printed in dmesg. But actually

mmc0 = 0000:00:01.0
mmc1 = 0000:00:01.2
mmc2 = 0000:00:01.3

And this has been so for like 8 years. See f.i. 
https://github.com/edison-fw/meta-intel-edison/issues/135
(this is with Yocto, so using systemd, the issue discussed there is not 
related to this but to card detection iirc)

> So you have mmc2 instantiated before mmc1 even before the patch. This
> happens because we now have
> 
> 		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
> 
> in sdhci_driver structure in drivers/mmc/host/sdhci-pci-core.c. It just
> happened that even with asynchronous probing your storage did end up on
> mmc0 originally and you were happy.
> 
> I wonder, could you please post entire dmesg for your system?
> 
>>
>>>>> That said, device trees are full of stuff like this:
>>>>>
>>>>>          aliases {
>>>>>                  serial0 = &uart_AO;
>>>>>                  mmc0 = &sd_card_slot;
>>>>>                  mmc1 = &sdhc;
>>>>>          };
>>>>
>>>> And Rob, AFAIU, is against aliases.
> 
> Rob might not want them, but they are the reality and are present for
> multiple classes of devices and I believe are here to stay.
> 
>>>>
>>>>> Notice how this enumeration gets defined by the aliases.
>>>>>
>>>>> Can you do the same with device properties? (If anyone can
>>>>> answer that question it's Dmitry!)
>>>>
>>>> No, and why should we?
>>>
>>> Because device properties are not device tree, they are just some
>>> Linux thing so we can do whatever we want. Just checking if
>>> Dmitry has some idea that would solve this for good, he usually
>>> replies quickly.
>>
>> OK.
> 
> I think the right answer is "fix the userspace" really in this case. We
> could also try extend of_alias_get_id() to see if we could pass some
> preferred numbering on x86. But this will again be fragile if the
> knowledge resides in the driver and is not tied to a particular board
> (as it is in DT case): there could be multiple controllers, things will
> be shifting board to board...
> 
> Thanks.
>