linux-kernel - Re: [PATCH] soc: imx8m: Probe the SoC driver late

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Message-Id: <4897ec78-b82c-415d-88dd-5092fa009f77@app.fastmail.com>
Date: Wed, 25 Sep 2024 16:31:00 +0000
From: "Arnd Bergmann" <arnd@...db.de>
To: "Marek Vasut" <marex@...x.de>, linux-arm-kernel@...ts.infradead.org
Cc: kernel@...electronics.com,
 "AngeloGioacchino Del Regno" <angelogioacchino.delregno@...labora.com>,
 "Fabio Estevam" <festevam@...il.com>,
 "Jeff Johnson" <quic_jjohnson@...cinc.com>,
 "Neil Armstrong" <neil.armstrong@...aro.org>,
 "Pengutronix Kernel Team" <kernel@...gutronix.de>,
 "Saravana Kannan" <saravanak@...gle.com>,
 "Sascha Hauer" <s.hauer@...gutronix.de>, "Shawn Guo" <shawnguo@...nel.org>,
 imx@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] soc: imx8m: Probe the SoC driver late

On Wed, Sep 25, 2024, at 16:09, Marek Vasut wrote:
> On 9/25/24 6:04 PM, Arnd Bergmann wrote:
>> On Wed, Sep 25, 2024, at 16:00, Marek Vasut wrote:
>>> With driver_async_probe=* on kernel command line, the following trace is
>>> produced because on i.MX8M Plus hardware because the soc-imx8m.c driver
>>> calls of_clk_get_by_name() which returns -EPROBE_DEFER because the clock
>>> driver is not yet probed. This was not detected during regular testing
>>> without driver_async_probe.
>>>
>>> Attempt to fix it by probing the SoC driver late, but I don't think that
>>> is the correct approach here.
>> 
>> I think the correct fix would be to propagate the -EPROBE_DEFER
>> and return that from imx8_soc_init(), so it gets retried again
>> after the clock driver.
> I already tried that, but if I return -EPROBE_DEFER from 
> device_initcall, it doesn't get retriggered . I suspect EPROBE_DEFER 
> works only for proper drivers ?

Right, of course. And unfortunately it can't just register to
the fsl,imx8mm-anatop/fsl,imx8mm-ocotp/... nodes because they
all have a driver already.

On the other hand, making it a late_initcall() defeats the
purpose of the driver because then it can't be used by other
drivers with soc_device_match(), resulting in incorrect
behavior when another driver relies on this to enable
a chip revision specific workaround.

     Arnd