linux-kernel - Re: [PATCH 31/34] spi: remove incorrect of_match

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Message-Id: <e5ebcbac-f445-4a48-a40f-7aa606c7d460@app.fastmail.com>
Date: Thu, 04 Apr 2024 00:19:41 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Andy Shevchenko" <andy.shevchenko@...il.com>,
 Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Cc: "Mark Brown" <broonie@...nel.org>, "Arnd Bergmann" <arnd@...nel.org>,
 linux-kernel@...r.kernel.org,
 "Neil Armstrong" <neil.armstrong@...aro.org>,
 "Kevin Hilman" <khilman@...libre.com>,
 Heiko Stübner <heiko@...ech.de>,
 "Andi Shyti" <andi.shyti@...nel.org>,
 "Krzysztof Kozlowski" <krzysztof.kozlowski@...aro.org>,
 "Jerome Brunet" <jbrunet@...libre.com>,
 "Martin Blumenstingl" <martin.blumenstingl@...glemail.com>,
 "Alim Akhtar" <alim.akhtar@...sung.com>,
 "Li Zetao" <lizetao1@...wei.com>,
 "Jonathan Cameron" <Jonathan.Cameron@...wei.com>,
 "Rob Herring" <robh@...nel.org>,
 "Yang Yingliang" <yangyingliang@...wei.com>,
 "Andy Shevchenko" <andriy.shevchenko@...ux.intel.com>,
 "Luis de Arquer" <luis.dearquer@...rtim.com>,
 "Tudor Ambarus" <tudor.ambarus@...aro.org>,
 "Sam Protsenko" <semen.protsenko@...aro.org>,
 "Peter Griffin" <peter.griffin@...aro.org>,
 "Jaewon Kim" <jaewon02.kim@...sung.com>, linux-spi@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-amlogic@...ts.infradead.org,
 linux-rockchip@...ts.infradead.org, linux-samsung-soc@...r.kernel.org
Subject: Re: [PATCH 31/34] spi: remove incorrect of_match_ptr annotations

On Wed, Apr 3, 2024, at 23:13, Andy Shevchenko wrote:
> Wed, Apr 03, 2024 at 11:05:51PM +0200, Uwe Kleine-König kirjoitti:
>> On Wed, Apr 03, 2024 at 10:56:58AM +0100, Mark Brown wrote:
>> > On Wed, Apr 03, 2024 at 10:06:49AM +0200, Arnd Bergmann wrote:
>> > 
>> > > These appear to all be copied from the same original driver, so fix them at the
>> > > same time by removing the unnecessary of_match_ptr() annotation. As far as I
>> > > can tell, all these drivers are only actually used on configurations that
>> > > have CONFIG_OF enabled.
>> > 
>> > Why are we not fixing of_match_ptr() here, or at least adding the ifdefs
>> > in case someone does end up wanting to run without OF?
>> 
>> Fixing of_match_ptr =
>> 
>> diff --git a/include/linux/of.h b/include/linux/of.h
>> index a0bedd038a05..d980bccffda0 100644
>> --- a/include/linux/of.h
>> +++ b/include/linux/of.h
>> @@ -890,7 +890,7 @@ static inline const void *of_device_get_match_data(const struct device *dev)
>>  	return NULL;
>>  }
>>  
>> -#define of_match_ptr(_ptr)	NULL
>> +#define of_match_ptr(_ptr)	(0 ? (_ptr) : NULL)

This would require removing several hundred "#ifdef CONFIG_OF"
checks around the of_device_id tables at the same time
unfortunately. Most of those are completely unnecessary, so
if we wanted to remove those, we should remove the of_match_ptr()
instances at the same time.

>>  #define of_match_node(_matches, _node)	NULL
>>  #endif /* CONFIG_OF */
>>  
>> ?
>> 
>> Assuming this helps, I agree this would be the better fix.
>
> Why? I mean why do we need to even have this API? It's always
> good to know which devices are supported by the module even
> if you have no need in such support or it's not compiled in.
> One of the reasons why is to be able to google for compatible hardware,
> for example.

As far as I can tell, the of_match_ptr() helper was a historic
mistake, it makes pretty much no sense in its current form.

The version that Uwe proposes would have made sense but we
can't change it now.

      Arnd