linux-kernel - Re: i8k: move driver from char to hwmon

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Date:	Wed, 22 Apr 2015 10:23:04 +0200
From:	Jean Delvare <jdelvare@...e.de>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Pali Rohár <pali.rohar@...il.com>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Steven Honeyman <stevenhoneyman@...il.com>,
	Valdis.Kletnieks@...edu,
	Jochen Eisinger <jochen@...guin-breeder.org>,
	Gabriele Mazzotta <gabriele.mzt@...il.com>,
	linux-kernel@...r.kernel.org, lm-sensors@...sensors.org
Subject: Re: i8k: move driver from char to hwmon

On Sun, 22 Feb 2015 10:11:16 -0800, Guenter Roeck wrote:
> On 02/22/2015 09:44 AM, Pali Rohár wrote:
> > What about CONFIG_DELLDIAG (or DELLSMM or CONFIG_SENSORS_*) for
> > mandatory core & hwmon code and (keep existing) CONFIG_I8K for
> > /proc/i8k?
> 
> One option might be to leave CONFIG_I8K more or less alone
> (it is in arch/x86/Kconfig anyway, which is odd by itself),
> but add something like
> 	select SENSORS_DELL
> 	select I8K_PROC
> to it. Then add new config options SENSORS_DELL and
> I8K_PROC to drivers/hwmon/Kconfig.

On a related note...

Changing Kconfig symbol names is allowed, it has happened a lot in the
past, although we should make it the least painful possible for the
users.

I thought about it earlier as I considered several times the
possibility to rename all CONFIG_SENSORS_* symbols to CONFIG_HWMON_*
for consistency. I never actually took the time to do it, but here's
how I would do it, taking the lm75 driver as an example.

As a first step, I would introduce a hidden symbol that would be
selected automatically by the existing symbol:

 drivers/hwmon/Kconfig  |    4 ++++
 drivers/hwmon/Makefile |    2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

--- linux-4.1-rc0.orig/drivers/hwmon/Kconfig	2015-04-22 09:54:21.965974944 +0200
+++ linux-4.1-rc0/drivers/hwmon/Kconfig	2015-04-22 10:10:16.974551936 +0200
@@ -909,10 +909,14 @@ config SENSORS_LM73
 	  This driver can also be built as a module.  If so, the module
 	  will be called lm73.
 
+config HWMON_LM75
+	tristate
+
 config SENSORS_LM75
 	tristate "National Semiconductor LM75 and compatibles"
 	depends on I2C
 	depends on THERMAL || !THERMAL_OF
+	select HWMON_LM75
 	help
 	  If you say yes here you get support for one common type of
 	  temperature sensor chip, with models including:
--- linux-4.1-rc0.orig/drivers/hwmon/Makefile	2015-04-22 09:54:21.965974944 +0200
+++ linux-4.1-rc0/drivers/hwmon/Makefile	2015-04-22 10:09:03.712048849 +0200
@@ -85,7 +85,7 @@ obj-$(CONFIG_SENSORS_LINEAGE)	+= lineage
 obj-$(CONFIG_SENSORS_LM63)	+= lm63.o
 obj-$(CONFIG_SENSORS_LM70)	+= lm70.o
 obj-$(CONFIG_SENSORS_LM73)	+= lm73.o
-obj-$(CONFIG_SENSORS_LM75)	+= lm75.o
+obj-$(CONFIG_HWMON_LM75)	+= lm75.o
 obj-$(CONFIG_SENSORS_LM77)	+= lm77.o
 obj-$(CONFIG_SENSORS_LM78)	+= lm78.o
 obj-$(CONFIG_SENSORS_LM80)	+= lm80.o

Running "make oldconfig" after that silently selects the new symbol as
needed:

--- .config.old	2015-04-20 10:16:42.645359313 +0200
+++ .config	2015-04-22 10:09:09.358164599 +0200
@@ -2805,6 +2805,7 @@
 CONFIG_SENSORS_LM63=m
 # CONFIG_SENSORS_LM70 is not set
 CONFIG_SENSORS_LM73=m
+CONFIG_HWMON_LM75=m
 CONFIG_SENSORS_LM75=m
 CONFIG_SENSORS_LM77=m
 CONFIG_SENSORS_LM78=m

Then I would let several kernel versions pass. After a year maybe, or 5
kernel versions, we could get rid of the original symbol:

 drivers/hwmon/Kconfig |    4 ----
 1 file changed, 4 deletions(-)

--- linux-4.1-rc0.orig/drivers/hwmon/Kconfig	2015-04-22 10:08:39.017542771 +0200
+++ linux-4.1-rc0/drivers/hwmon/Kconfig	2015-04-22 10:09:57.376149603 +0200
@@ -910,13 +910,9 @@ config SENSORS_LM73
 	  will be called lm73.
 
 config HWMON_LM75
-	tristate
-
-config SENSORS_LM75
 	tristate "National Semiconductor LM75 and compatibles"
 	depends on I2C
 	depends on THERMAL || !THERMAL_OF
-	select HWMON_LM75
 	help
 	  If you say yes here you get support for one common type of
 	  temperature sensor chip, with models including:

Again running "make oldconfig" will do the right thing silently:

--- .config.old	2015-04-22 10:09:09.358164599 +0200
+++ .config	2015-04-22 10:10:02.942263851 +0200
@@ -2806,7 +2806,6 @@
 # CONFIG_SENSORS_LM70 is not set
 CONFIG_SENSORS_LM73=m
 CONFIG_HWMON_LM75=m
-CONFIG_SENSORS_LM75=m
 CONFIG_SENSORS_LM77=m
 CONFIG_SENSORS_LM78=m
 CONFIG_SENSORS_LM80=m

This allows for a transparent migration to the new names from a user's
perspective, as long as they do not jump directly from the original
state to the final state. Maybe something like that can be done for
CONFIG_I8K if you want to rename it.

-- 
Jean Delvare
SUSE L3 Support
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