Re: [PATCH 5.6 019/194] net: Make PTP-specific drivers depend on PTP_1588_CLOCK

From: Sasha Levin
Date: Mon May 18 2020 - 16:25:40 EST


On Mon, May 18, 2020 at 09:13:54PM +0300, Grygorii Strashko wrote:
Hi Greg,

On 18/05/2020 20:35, Greg Kroah-Hartman wrote:
From: Clay McClure <clay@xxxxxxxxxxx>

[ Upstream commit b6d49cab44b567b3e0a5544b3d61e516a7355fad ]

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() but merely
`imply PTP_1588_CLOCK` and found five 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

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

Change them from `imply PTP_1588_CLOCK` [2] to `depends on PTP_1588_CLOCK`.
I'm not using `select PTP_1588_CLOCK` here because PTP_1588_CLOCK has
its own dependencies, which `select` would not transitively apply.

Additionally, remove the `select NET_PTP_CLASSIFY` from CPTS_TI_MOD;
PTP_1588_CLOCK already selects that.

[1]: https://lore.kernel.org/lkml/c04458ed-29ee-1797-3a11-7f3f560553e6@xxxxxx/

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

Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Richard Cochran <richardcochran@xxxxxxxxx>
Cc: Nicolas Pitre <nico@xxxxxxxxxxx>
Cc: Grygorii Strashko <grygorii.strashko@xxxxxx>
Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Fixes: d1cbfd771ce8 ("ptp_clock: Allow for it to be optional")
Signed-off-by: Clay McClure <clay@xxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---

Could you drop this patch, pls?
it's not for stable and can cause build failures.

My bad - now dropped. Sorry!

--
Thanks,
Sasha