linux-kernel - Re: [PATCH 2/4] iio: dac: ad5755: mark OF related data as maybe unused

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Message-ID: <20230311183121.577eb52b@jic23-huawei>
Date:   Sat, 11 Mar 2023 18:31:21 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Marek Vasut <marek.vasut@...il.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        Robert Eshleman <bobbyeshleman@...il.com>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] iio: dac: ad5755: mark OF related data as maybe
 unused

On Sat, 11 Mar 2023 13:25:33 +0100
Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org> wrote:

> On 11/03/2023 13:22, Jonathan Cameron wrote:
> > On Sat, 11 Mar 2023 12:14:55 +0100
> > Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org> wrote:
> >   
> >> The driver can be compile tested with !CONFIG_OF making certain data
> >> unused (of_device_id is not used for device matching):  
> > 
> > It should be used for device matching I think, so I'd rather see
> > it assigned for that purpose than hiding the issue.  
> 
> That would require testing and changes. The device matching is via SPI
> table which has device data. Probably adding OF matching would require
> bigger changes to for handling the match data.
> 
> This was intentional design in this driver, so we are not hiding here
> anything.

I doubt it was intentional. Mostly people do this because the magic
fallbacks to find the spi_device_id entry work.

If we'd noticed at review time it would not have gone in like this.
Note that the spi_match_id() use of_modalias_node() which has stripped the
vendor id off the compatible then matches against the spi_device_id
table.

So it 'should' just work.  Now ideally we'd switch to
spi_get_device_match_data() but that needs more significant changes.
Though simple enough ones that review would be enough.

Just need to use pointers to the ad75755_chip_info_tbl entries
rather than the enum in both the spi id table and the of one - this
avoids the issue with the enum value of 0 counting as a failed match.

> 
> > 
> >   
> >>
> >>   drivers/iio/dac/ad5755.c:865:34: error: ‘ad5755_of_match’ defined but not used [-Werror=unused-const-variable=]  
> 
> >   
> 
> Best regards,
> Krzysztof
>