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

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Date:   Thu, 16 Mar 2023 15:13:25 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     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
Cc:     Javier Martinez Canillas <javierm@...hat.com>
Subject: Re: [PATCH 1/3] platform: olpc: mark SPI related data as maybe unused

Hi,

On 3/16/23 15:07, Krzysztof Kozlowski wrote:
> On 16/03/2023 13:50, Hans de Goede wrote:
>> Hi Krzysztof,
>>
>> On 3/12/23 14:26, Krzysztof Kozlowski wrote:
>>> The driver can be compile tested as built-in making certain data unused:
>>>
>>>   drivers/platform/olpc/olpc-xo175-ec.c:737:35: error: ‘olpc_xo175_ec_id_table’ defined but not used [-Werror=unused-const-variable=]
>>>
>>> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>>> ---
>>>  drivers/platform/olpc/olpc-xo175-ec.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/platform/olpc/olpc-xo175-ec.c b/drivers/platform/olpc/olpc-xo175-ec.c
>>> index 4823bd2819f6..04573495ef5a 100644
>>> --- a/drivers/platform/olpc/olpc-xo175-ec.c
>>> +++ b/drivers/platform/olpc/olpc-xo175-ec.c
>>> @@ -734,7 +734,7 @@ static const struct of_device_id olpc_xo175_ec_of_match[] = {
>>>  };
>>>  MODULE_DEVICE_TABLE(of, olpc_xo175_ec_of_match);
>>>  
>>> -static const struct spi_device_id olpc_xo175_ec_id_table[] = {
>>> +static const struct spi_device_id olpc_xo175_ec_id_table[] __maybe_unused = {
>>>  	{ "xo1.75-ec", 0 },
>>>  	{}
>>>  };
>>>  MODULE_DEVICE_TABLE(spi, olpc_xo175_ec_id_table);
>>
>> The whole presence of the olpc_xo175_ec_id_table[] seems to make little sense.
>>
>> This should be referenced by:
>>
>> static struct spi_driver olpc_xo175_ec_spi_driver = {
>>
>> Like this:
>>
>>         .probe          = olpc_xo175_ec_probe,
>>         .remove         = olpc_xo175_ec_remove,
>> +       .id_table       = olpc_xo175_ec_id_table,
> 
> Yes, it should.
> 
>>
>> Otherwise those ids cannot be used to load the driver the non DT/of way. Since the driver assumingly does actually bind already this means that it is only used the DT/of way and it seems to me that the whole olpc_xo175_ec_id_table[] can be removed entirely.
>>
>> 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.

Can you do a v2 (of just this patch) adding an id_table entry to olpc_xo175_ec_spi_driver rather then using __maybe_unused ?

Regards,

Hans