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Date: Wed, 7 Dec 2022 09:19:15 -0800 From: Randy Dunlap <rdunlap@...radead.org> To: Arnd Bergmann <arnd@...db.de>, Peter Rosin <peda@...ntia.se>, Linus Torvalds <torvalds@...ux-foundation.org> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Andrew Morton <akpm@...ux-foundation.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v2] mux: remove the Kconfig question for the subsystem On 12/7/22 00:41, Arnd Bergmann wrote: > On Tue, Dec 6, 2022, at 23:20, Randy Dunlap wrote: >> On 7/4/17 01:22, Peter Rosin wrote: >>> The MULTIPLEXER question in the Kconfig might be confusing and is >>> of dubious value. Remove it. This makes consumers responsible for >>> selecting MULTIPLEXER, which they already do. >>> >>> Signed-off-by: Peter Rosin <peda@...ntia.se> >> >> >> How does a user enable any of the 4 drivers in drivers/mux/Kconfig unless >> some other totally unrelated driver has just happened to select MULTIPLEXER >> so that the mux driver menu is visible to them? > > We have this mechanism for a few subsystems, LEDS_CLASS/NEW_LEDS and > CRYPTO being more common examples. > > The idea clearly is that there is no need for the subsystem if no > drivers call into it. This works if every single driver calling > \(devm_\|\)mux_control_get also results in 'select MULTIPLEXER' > in Kconfig, and none of them ever uses 'depends on MULTIPLEXER'. > I think this is used correctly most of the time in mainline: > git grep '\<\(mux/consumer.h\|MULTIPLEXER\)\>' indicates that > PHY_J721E_WIZ and MTD_PHYSMAP_BT1_ROM may not actually need it, > but that is fairly harmless. Yes, sure. > For the other subsystems I mentioned, there are occasionally > problems with missing 'select' that tend to be a pain to find, > compared to subsystems consistently using 'depends on', which > show up as link failures in randconfig builds. I find that various drivers mixing the use of "select" and "depends on" is problematic. However, there was no answer for the original question: How does a user enable the 4 Kconfig symbols in drivers/mux/Kconfig if some other random driver has not selected MULTIPLEXER? I.e.: config MUX_ADG792A tristate "Analog Devices ADG792A/ADG792G Multiplexers" config MUX_ADGS1408 tristate "Analog Devices ADGS1408/ADGS1409 Multiplexers" config MUX_GPIO tristate "GPIO-controlled Multiplexer" config MUX_MMIO tristate "MMIO/Regmap register bitfield-controlled Multiplexer" OK, MUX_MMIO is selected from some other drivers, but if that is not done, how can the first 3 be enabled by a user? thanks. -- ~Randy
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