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

[Sasha Levin]

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