linux-kernel - Re: [PATCH v1 4/4] of: platform: Batch fwnode parsing when adding all top level devices

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Date:   Tue, 19 May 2020 12:32:30 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Len Brown <lenb@...nel.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Ji Luo <ji.luo@....com>,
        Linux Samsung SOC <linux-samsung-soc@...r.kernel.org>
Subject: Re: [PATCH v1 4/4] of: platform: Batch fwnode parsing when adding
 all top level devices

Hi

On 19.05.2020 09:11, Marek Szyprowski wrote:
> On 19.05.2020 08:48, Saravana Kannan wrote:
>> On Mon, May 18, 2020 at 11:25 PM Marek Szyprowski
>> <m.szyprowski@...sung.com> wrote:
>>> On 15.05.2020 07:35, Saravana Kannan wrote:
>>>> The fw_devlink_pause() and fw_devlink_resume() APIs allow batching the
>>>> parsing of the device tree nodes when a lot of devices are added. This
>>>> will significantly cut down parsing time (as much a 1 second on some
>>>> systems). So, use them when adding devices for all the top level 
>>>> device
>>>> tree nodes in a system.
>>>>
>>>> Signed-off-by: Saravana Kannan <saravanak@...gle.com>
>>> This patch recently landed in linux-next 20200518. Sadly, it causes
>>> regression on Samsung Exynos5433-based TM2e board:
>>>
>>> ...
>>>
>>> Both issues, the lack of DMA for SPI device and Synchronous abort in 
>>> I2S
>>> probe are new after applying this patch. I'm trying to investigate 
>>> which
>>> resources are missing and why. The latter issue means typically that 
>>> the
>>> registers for the given device has been accessed without enabling the
>>> needed clocks or power domains.
>> Did you try this copy-pasta fix that I sent later?
>> https://lore.kernel.org/lkml/20200517173453.157703-1-saravanak@google.com/ 
>>
>>
>> Not every system would need it (my test setup didn't), but it helps 
>> some cases.
>>
>> If that fix doesn't help, then some tips for debugging the failing 
>> drivers.
>> What this pause/resume patch effectively (not explicitly) does is:
>> 1. Doesn't immediately probe the devices as they are added in
>> of_platform_default_populate_init()
>> 2. Adds them in order to the deferred probe list.
>> 3. Then kicks off deferred probe on them in the order they were added.
>>
>> These drivers are just not handling -EPROBE_DEFER correctly or
>> assuming probe order and that's causing these issues.
>>
>> So, we can either fix that or you can try adding some code to flush
>> the deferred probe workqueue at the end of fw_devlink_resume().
>>
>> Let me know how it goes.
>
> So far it looks that your patch revealed a hidden issue in exynos5433 
> clocks configuration, because adding clk_ignore_unused parameter to 
> kernel command line fixes the boot. I'm still investigating it, so 
> probable you can ignore my regression report. I will let you know asap 
> I finish checking it.
>
Okay, I confirm that the issue is in the Exynos I2S driver and 
Exynos5433 clock provider. I've posted a quick workaround. I'm sorry for 
the noise, your patch is fine.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland