linux-kernel - Re: [PATCH v5 0/7] can: refactoring of can-dev module and of Kbuild

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Date:   Tue, 7 Jun 2022 11:49:30 +0900
From:   Vincent MAILHOL <mailhol.vincent@...adoo.fr>
To:     Oliver Hartkopp <socketcan@...tkopp.net>
Cc:     Marc Kleine-Budde <mkl@...gutronix.de>,
        linux-can <linux-can@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Max Staudt <max@...as.org>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v5 0/7] can: refactoring of can-dev module and of Kbuild

On Tue. 7 Jun. 2022 at 04:43, Oliver Hartkopp <socketcan@...tkopp.net> wrote:
>
> Hi Vincent,
>
> great work!

Thanks!

> On 04.06.22 18:29, Vincent Mailhol wrote:
>
> > * menu after this series *
> >
> > Network device support
> >    symbol: CONFIG_NETDEVICES
> >    |
> >    +-> CAN Device Drivers
> >        symbol: CONFIG_CAN_DEV
> >        |
> >        +-> software/virtual CAN device drivers
> >        |   (at time of writing: slcan, vcan, vxcan)
> >        |
> >        +-> CAN device drivers with Netlink support
> >            symbol: CONFIG_CAN_NETLINK (matches previous CONFIG_CAN_DEV)
> >            |
> >            +-> CAN bit-timing calculation (optional for all drivers)
> >            |   symbol: CONFIG_CAN_BITTIMING
                           ^^^^^^^^^^^^^^^^^^^^
Typo: the symbol is CONFIG_CAN_*CALC*_BITTIMING. I made that typo
twice in the cover letter (once in each diagram). The patches and
their comments remain correct.

> >            |
> >            +-> All other CAN devices not relying on RX offload
> >            |
> >            +-> CAN rx offload
> >                symbol: CONFIG_CAN_RX_OFFLOAD
>
> Is this still true in patch series 5?
>
> If I understood it correctly CONFIG_CAN_BITTIMING and
> CONFIG_CAN_RX_OFFLOAD can be enabled by the user and
> (alternatively/additionally) the selection of "flexcan, m_can, mcp251xfd
> and ti_hecc" enables CONFIG_CAN_RX_OFFLOAD too.
>
> Right?

Yes, this is correct. Maybe what troubles you is the meaning of the
"x --> y" arrow in the graph. I said it denotes that "y depends on x".
Here "depends on" has a loose meaning. It translates to either:
  * Feature Y is encapsulated in Kbuild by some "if X/endif" and won't
show up unless X is selected.
  * Feature Y has a "selects X" tag and will forcibly enable X if selected.

CONFIG_CAN_*CALC*_BITTIMING is on the left side of an arrow starting
from CONFIG_CAN_NETLINK so it "depends" on CONFIG_CAN_NETLINK. On the
other hand, CONFIG_CAN_*CALC*_BITTIMING does not have any arrow
starting from it so indeed, it can be enabled by the user
independently of the other features as long as CONFIG_CAN_NETLINK is
selected.
CONFIG_CAN_RX_OFFLOAD is also on the left side of an arrow starting
from CONFIG_CAN_NETLINK. Furthermore, there is an arrow starting from
CONFIG_CAN_RX_OFFLOAD going to the "rx offload drivers". So those
drivers need CONFIG_CAN_RX_OFFLOAD (which is implemented using the
"selects CONFIG_CAN_RX_OFFLOAD"). However, CONFIG_CAN_RX_OFFLOAD can
be selected independently of the "rx offload drivers" as long as its
CONFIG_CAN_NETLINK dependency is met.

So I think that the diagram is correct. Maybe rephrasing the cover
letter as below would address your concerns?

| Below diagrams illustrate the changes made. The arrow symbol "X --> Y"
| denotes that "Y needs X". Most of the time, it is implemented using "if X"
| and "endif" predicates in X’s Kbuild to encapsulate Y so that Y
| does not show up unless X is selected. The exception is rx
| offload which is implemented by adding a "selects
| CONFIG_CAN_RX_OFFLOAD" tag in Y’s Kbuild.

> >                |
> >                +-> CAN devices relying on rx offload
> >                    (at time of writing: flexcan, m_can, mcp251xfd and ti_hecc)

Yours sincerely,
Vincent Mailhol