Re: [PATCH net-next v3] ethernet: fix PTP_1588_CLOCK dependencies

From: Shannon Nelson
Date: Wed Aug 04 2021 - 16:53:14 EST

On 8/4/21 4:57 AM, Arnd Bergmann wrote:
From: Arnd Bergmann <arnd@xxxxxxxx>

The 'imply' keyword does not do what most people think it does, it only
politely asks Kconfig to turn on another symbol, but does not prevent
it from being disabled manually or built as a loadable module when the
user is built-in. In the ICE driver, the latter now causes a link failure:

aarch64-linux-ld: drivers/net/ethernet/intel/ice/ice_main.o: in function `ice_eth_ioctl':
ice_main.c:(.text+0x13b0): undefined reference to `ice_ptp_get_ts_config'
ice_main.c:(.text+0x13b0): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `ice_ptp_get_ts_config'
aarch64-linux-ld: ice_main.c:(.text+0x13bc): undefined reference to `ice_ptp_set_ts_config'
ice_main.c:(.text+0x13bc): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `ice_ptp_set_ts_config'
aarch64-linux-ld: drivers/net/ethernet/intel/ice/ice_main.o: in function `ice_prepare_for_reset':
ice_main.c:(.text+0x31fc): undefined reference to `ice_ptp_release'
ice_main.c:(.text+0x31fc): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `ice_ptp_release'
aarch64-linux-ld: drivers/net/ethernet/intel/ice/ice_main.o: in function `ice_rebuild':

This is a recurring problem in many drivers, and we have discussed
it several times befores, without reaching a consensus. I'm providing
a link to the previous email thread for reference, which discusses
some related problems.

To solve the dependency issue better than the 'imply' keyword, introduce a
separate Kconfig symbol "CONFIG_PTP_1588_CLOCK_OPTIONAL" that any driver
can depend on if it is able to use PTP support when available, but works
fine without it. Whenever CONFIG_PTP_1588_CLOCK=m, those drivers are
then prevented from being built-in, the same way as with a 'depends on
PTP_1588_CLOCK || !PTP_1588_CLOCK' dependency that does the same trick,
but that can be rather confusing when you first see it.

Since this should cover the dependencies correctly, the IS_REACHABLE()
hack in the header is no longer needed now, and can be turned back
into a normal IS_ENABLED() check. Any driver that gets the dependency
wrong will now cause a link time failure rather than being unable to use
PTP support when that is in a loadable module.

However, the two recently added ptp_get_vclocks_index() and
ptp_convert_timestamp() interfaces are only called from builtin code with
ethtool and socket timestamps, so keep the current behavior by stubbing
those out completely when PTP is in a loadable module. This should be
addressed properly in a follow-up.

As Richard suggested, we may want to actually turn PTP support into a
'bool' option later on, preventing it from being a loadable module
altogether, which would be one way to solve the problem with the ethtool

Fixes: 06c16d89d2cb ("ice: register 1588 PTP clock device object for E810 devices")
Cc: Richard Cochran <richardcochran@xxxxxxxxx>
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
Changes in v3:
- rewrite to introduce a new PTP_1588_CLOCK_OPTIONAL symbol
- use it for all driver, not just Intel's
- change IS_REACHABLE() to IS_ENABLED() in the header

Changes in v2:
- include a missing patch hunk
- link to a previous discussion with Richard Cochran
drivers/net/dsa/mv88e6xxx/Kconfig | 1 +
drivers/net/dsa/ocelot/Kconfig | 2 +
drivers/net/ethernet/amd/Kconfig | 2 +-
drivers/net/ethernet/broadcom/Kconfig | 6 +--
drivers/net/ethernet/cadence/Kconfig | 1 +
drivers/net/ethernet/cavium/Kconfig | 4 +-
drivers/net/ethernet/freescale/Kconfig | 2 +-
drivers/net/ethernet/hisilicon/Kconfig | 2 +-
drivers/net/ethernet/intel/Kconfig | 14 +++---
drivers/net/ethernet/mellanox/mlx4/Kconfig | 2 +-
.../net/ethernet/mellanox/mlx5/core/Kconfig | 2 +-
drivers/net/ethernet/mellanox/mlxsw/Kconfig | 2 +-
drivers/net/ethernet/mscc/Kconfig | 2 +
drivers/net/ethernet/oki-semi/pch_gbe/Kconfig | 1 +
drivers/net/ethernet/pensando/Kconfig | 2 +-


drivers/net/ethernet/qlogic/Kconfig | 2 +-
diff --git a/drivers/net/ethernet/pensando/Kconfig b/drivers/net/ethernet/pensando/Kconfig
index 202973a82712..3f7519e435b8 100644
--- a/drivers/net/ethernet/pensando/Kconfig
+++ b/drivers/net/ethernet/pensando/Kconfig
@@ -20,7 +20,7 @@ if NET_VENDOR_PENSANDO
config IONIC
tristate "Pensando Ethernet IONIC Support"
depends on 64BIT && PCI
- depends on PTP_1588_CLOCK || !PTP_1588_CLOCK
+ depends on PTP_1588_CLOCK_OPTIONAL
select DIMLIB

Acked-by: Shannon Nelson <snelson@xxxxxxxxxxx>