[PATCH] net: Select PTP_1588_CLOCK in PTP-specific drivers

[Clay McClure <clay@daemons.net>]

Commit d1cbfd771ce8 ("ptp_clock: Allow for it to be optional") changed
all PTP-capable Ethernet drivers from `select PTP_1588_CLOCK` to `imply
PTP_1588_CLOCK`, "in order to break the hard dependency between the PTP
clock subsystem and ethernet drivers capable of being clock providers."
As a result it is possible to build PTP-capable Ethernet drivers without
the PTP subsystem by deselecting PTP_1588_CLOCK. Drivers are required to
handle the missing dependency gracefully.

Some PTP-capable Ethernet drivers (e.g., TI_CPSW) factor their PTP code
out into separate drivers (e.g., TI_CPTS_MOD). The above commit also
changed these PTP-specific drivers to `imply PTP_1588_CLOCK`, making it
possible to build them without the PTP subsystem. But as Grygorii
Strashko noted in [1]:

On Wed, Apr 22, 2020 at 02:16:11PM +0300, Grygorii Strashko wrote:

> Another question is that CPTS completely nonfunctional in this case and
> it was never expected that somebody will even try to use/run such
> configuration (except for random build purposes).

In my view, enabling a PTP-specific driver without the PTP subsystem is
a configuration error made possible by the above commit. Kconfig should
not allow users to create a configuration with missing dependencies that
results in "completely nonfunctional" drivers.

I audited all network drivers that call ptp_clock_register() and found
six that look like PTP-specific drivers that are likely nonfunctional
without PTP_1588_CLOCK:

    NET_DSA_MV88E6XXX_PTP
    NET_DSA_SJA1105_PTP
    MACB_USE_HWSTAMP
    CAVIUM_PTP
    TI_CPTS_MOD
    PTP_1588_CLOCK_IXP46X

Note how they all reference PTP or timestamping in their name; this is a
clue that they depend on PTP_1588_CLOCK.

Change these drivers back [2] to `select PTP_1588_CLOCK`. Note that this
requires also selecting POSIX_TIMERS, a transitive dependency of
PTP_1588_CLOCK.

[1]: https://lkml.org/lkml/2020/4/22/1056

[2]: NET_DSA_SJA1105_PTP had never declared any type of dependency on
PTP_1588_CLOCK (`imply` or otherwise); adding it here seems appropriate.

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
Cc: Grygorii Strashko <grygorii.strashko@ti.com>
Fixes: d1cbfd771ce8 ("ptp_clock: Allow for it to be optional")
Signed-off-by: Clay McClure <clay@daemons.net>
---
 drivers/net/dsa/mv88e6xxx/Kconfig    | 3 ++-
 drivers/net/dsa/sja1105/Kconfig      | 2 ++
 drivers/net/ethernet/cadence/Kconfig | 3 ++-
 drivers/net/ethernet/cavium/Kconfig  | 3 ++-
 drivers/net/ethernet/ti/Kconfig      | 2 +-
 drivers/net/ethernet/xscale/Kconfig  | 3 ++-
 6 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/net/dsa/mv88e6xxx/Kconfig b/drivers/net/dsa/mv88e6xxx/Kconfig
index 6435020d690d..6e8250599eb1 100644
--- a/drivers/net/dsa/mv88e6xxx/Kconfig
+++ b/drivers/net/dsa/mv88e6xxx/Kconfig
@@ -25,7 +25,8 @@ config NET_DSA_MV88E6XXX_PTP
 	default n
 	depends on NET_DSA_MV88E6XXX_GLOBAL2
 	imply NETWORK_PHY_TIMESTAMPING
-	imply PTP_1588_CLOCK
+	select PTP_1588_CLOCK
+	select POSIX_TIMERS
 	help
 	  Say Y to enable PTP hardware timestamping on Marvell 88E6xxx switch
 	  chips that support it.
diff --git a/drivers/net/dsa/sja1105/Kconfig b/drivers/net/dsa/sja1105/Kconfig
index 0fe1ae173aa1..84349b6c8c44 100644
--- a/drivers/net/dsa/sja1105/Kconfig
+++ b/drivers/net/dsa/sja1105/Kconfig
@@ -20,6 +20,8 @@ tristate "NXP SJA1105 Ethernet switch family support"
 config NET_DSA_SJA1105_PTP
 	bool "Support for the PTP clock on the NXP SJA1105 Ethernet switch"
 	depends on NET_DSA_SJA1105
+	select PTP_1588_CLOCK
+	select POSIX_TIMERS
 	help
 	  This enables support for timestamping and PTP clock manipulations in
 	  the SJA1105 DSA driver.
diff --git a/drivers/net/ethernet/cadence/Kconfig b/drivers/net/ethernet/cadence/Kconfig
index 53b50c24d9c9..bc792c334903 100644
--- a/drivers/net/ethernet/cadence/Kconfig
+++ b/drivers/net/ethernet/cadence/Kconfig
@@ -36,7 +36,8 @@ config MACB_USE_HWSTAMP
 	bool "Use IEEE 1588 hwstamp"
 	depends on MACB
 	default y
-	imply PTP_1588_CLOCK
+	select PTP_1588_CLOCK
+	select POSIX_TIMERS
 	---help---
 	  Enable IEEE 1588 Precision Time Protocol (PTP) support for MACB.
 
diff --git a/drivers/net/ethernet/cavium/Kconfig b/drivers/net/ethernet/cavium/Kconfig
index 6a700d34019e..bae58c488792 100644
--- a/drivers/net/ethernet/cavium/Kconfig
+++ b/drivers/net/ethernet/cavium/Kconfig
@@ -54,7 +54,8 @@ config	THUNDER_NIC_RGX
 config CAVIUM_PTP
 	tristate "Cavium PTP coprocessor as PTP clock"
 	depends on 64BIT && PCI
-	imply PTP_1588_CLOCK
+	select PTP_1588_CLOCK
+	select POSIX_TIMERS
 	---help---
 	  This driver adds support for the Precision Time Protocol Clocks and
 	  Timestamping coprocessor (PTP) found on Cavium processors.
diff --git a/drivers/net/ethernet/ti/Kconfig b/drivers/net/ethernet/ti/Kconfig
index 89cec778cf2d..1177953790c5 100644
--- a/drivers/net/ethernet/ti/Kconfig
+++ b/drivers/net/ethernet/ti/Kconfig
@@ -92,7 +92,7 @@ config TI_CPTS_MOD
 	depends on TI_CPTS
 	default y if TI_CPSW=y || TI_KEYSTONE_NETCP=y || TI_CPSW_SWITCHDEV=y
 	select NET_PTP_CLASSIFY
-	imply PTP_1588_CLOCK
+	select PTP_1588_CLOCK
 	default m
 
 config TI_K3_AM65_CPSW_NUSS
diff --git a/drivers/net/ethernet/xscale/Kconfig b/drivers/net/ethernet/xscale/Kconfig
index 98aa7b8ddb06..82d4ec3c6398 100644
--- a/drivers/net/ethernet/xscale/Kconfig
+++ b/drivers/net/ethernet/xscale/Kconfig
@@ -30,7 +30,8 @@ config IXP4XX_ETH
 config PTP_1588_CLOCK_IXP46X
 	tristate "Intel IXP46x as PTP clock"
 	depends on IXP4XX_ETH
-	depends on PTP_1588_CLOCK
+	select PTP_1588_CLOCK
+	select POSIX_TIMERS
 	default y
 	help
 	  This driver adds support for using the IXP46X as a PTP
-- 
2.20.1