Re: [PATCH v1 5/5] driver core: Set fw_devlink=on by default

From: <Tudor.Ambarus@microchip.com>
To: <saravanak@google.com>
Cc: <gregkh@linuxfoundation.org>, <rafael@kernel.org>,
	<kernel-team@android.com>, <linux-kernel@vger.kernel.org>,
	<Jisheng.Zhang@synaptics.com>, <khilman@baylibre.com>,
	<john.stultz@linaro.org>, <nsaenzjulienne@suse.de>,
	<maz@kernel.org>, <geert@linux-m68k.org>,
	<Nicolas.Ferre@microchip.com>, <Ludovic.Desroches@microchip.com>,
	<alexandre.belloni@bootlin.com>, <Claudiu.Beznea@microchip.com>
Subject: Re: [PATCH v1 5/5] driver core: Set fw_devlink=on by default
Date: Thu, 28 Jan 2021 10:59:24 +0000	[thread overview]
Message-ID: <97a1fe96-ee2c-43cf-58fe-6ed910d3fb2c@microchip.com> (raw)
In-Reply-To: <CAGETcx-sZC4nKi9VKYUgaBnH4Kf3FraKEe+CMXxm_-DWjz9t5w@mail.gmail.com>

Hi, Saravana,

On 1/25/21 8:16 PM, Saravana Kannan wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> On Mon, Jan 25, 2021 at 9:05 AM <Tudor.Ambarus@microchip.com> wrote:
>>
>> Hi, Saravana,
>>
>> On 12/18/20 5:17 AM, Saravana Kannan wrote:
>>> Cyclic dependencies in some firmware was one of the last remaining
>>> reasons fw_devlink=on couldn't be set by default. Now that cyclic
>>> dependencies don't block probing, set fw_devlink=on by default.
>>>
>>> Setting fw_devlink=on by default brings a bunch of benefits (currently,
>>> only for systems with device tree firmware):
>>> * Significantly cuts down deferred probes.
>>> * Device probe is effectively attempted in graph order.
>>> * Makes it much easier to load drivers as modules without having to
>>>   worry about functional dependencies between modules (depmod is still
>>>   needed for symbol dependencies).
>>>
>>> If this patch prevents some devices from probing, it's very likely due
>>> to the system having one or more device drivers that "probe"/set up a
>>> device (DT node with compatible property) without creating a struct
>>> device for it.  If we hit such cases, the device drivers need to be
>>> fixed so that they populate struct devices and probe them like normal
>>> device drivers so that the driver core is aware of the devices and their
>>> status. See [1] for an example of such a case.
>>>
>>> [1] - https://lore.kernel.org/lkml/CAGETcx9PiX==mLxB9PO8Myyk6u2vhPVwTMsA5NkD-ywH5xhusw@mail.gmail.com/
>>> Signed-off-by: Saravana Kannan <saravanak@google.com>
>>
>> next-20210125 fails to boot on at91 sama5d2 platforms. No output is
>> seen, unless earlyprintk is enabled.
>>
>> I have bisected this to commit e590474768f1cc04 ("driver core: Set
>> fw_devlink=on by default").
>>
>> I've attached a log that I'm seeing on a sama5d2_xplained (sama5_defconfig
>> and arch/arm/boot/dts/at91-sama5d2_xplained.dts). I enabled the
>> following logs:
>> 1. The ones in device_links_check_suppliers()
>> 2. The ones in device_link_add()
>> 3. initcall_debug=1
>>
>> There seem to be some probe fails due to the pmc supplier not being ready:
>> calling  at_xdmac_init+0x0/0x18 @ 1
>> platform f0010000.dma-controller: probe deferral - supplier f0014000.pmc not ready
>> platform f0004000.dma-controller: probe deferral - supplier f0014000.pmc not ready
>> initcall at_xdmac_init+0x0/0x18 returned -19 after 19531 usecs
>>
>> calling  udc_driver_init+0x0/0x18 @ 1
>> platform 300000.gadget: probe deferral - supplier f0014000.pmc not ready
>> initcall udc_driver_init+0x0/0x18 returned -19 after 7524 usecs
>>
>> There are others too. I'm checking them.
> 
> Thanks Tudor. I'll look into this within a few days. I'm also looking
> into coming up with a more generic solution.
> 

I've sent a patch addressing this at:
https://lore.kernel.org/lkml/20210128104446.164269-1-tudor.ambarus@microchip.com/T/#u

Can you please take a look?
Cheers,
ta