linux-kernel - Re: [PATCH 1/3] platform: olpc: mark SPI related data as maybe unused

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Date:   Thu, 16 Mar 2023 18:31:07 +0100
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Hans de Goede <hdegoede@...hat.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Mark Gross <markgross@...nel.org>,
        Thadeu Lima de Souza Cascardo <cascardo@...oscopio.com>,
        Daniel Oliveira Nascimento <don@...t.com.br>,
        Mattia Dongili <malattia@...ux.it>,
        platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] platform: olpc: mark SPI related data as maybe unused

Hans de Goede <hdegoede@...hat.com> writes:

[...]

>>> Exposing modaliases for a non supported way of binding the driver does not really seem useful ?
>> 
>> However binding the device and module loading (uevent) uses sometimes
>> different pieces. Maybe something changed in kernel, but sometime ago
>> certain buses where sending uevent for module loading with one ID (e.g.
>> platform or spi bus) but device matching would be according to OF. Thus
>> if you did not have entries in spi_device_id, the module would not autoload.
>> 
>> It was exactly the case for example here:
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c46ed2281bbe4b84e6f3d4bdfb0e4e9ab813fa9d&context=30&ignorews=0&dt=0
>> 
>> You needed spi_device_id for proper module autoloading.
>> 
>> Unless something change in between in the kernel?
>
> Looks like your right, the spi_uevent() code always emits "spi:xxxxxxx" style modalias even for dt/of enumerated devices:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/spi/spi.c#n398
>
> So the table needs to stay.
>

Yeah, and in fact dropping the spi_device_id table will cause the kernel
to warn that an spi_device_id entry doesn't exist for a given of_device_id
entry since commit 5fa6863ba692 ("spi: Check we have a spi_device_id for
each DT compatible").

Fixing that is not trivial because a lot of drivers are rely on current
behaviour of the SPI core always returning a spi:<dev> modalias. So don't
even have an OF table, even when the SPI devices are instantiated by DT.

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat