Re: [PATCH v2] driver core: Remove device link creation limitation

From: Saravana Kannan <saravanak@google.com>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Dmitry Osipenko <digetx@gmail.com>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Linux PM <linux-pm@vger.kernel.org>,
	Lukas Wunner <lukas@wunner.de>, Jon Hunter <jonathanh@nvidia.com>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	"linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>,
	Thierry Reding <thierry.reding@gmail.com>
Subject: Re: [PATCH v2] driver core: Remove device link creation limitation
Date: Mon, 29 Jul 2019 15:13:34 -0700	[thread overview]
Message-ID: <CAGETcx-g+gbzgy0ZDKdMreRVWqnQyXLmuLRC4g5Zexyj5yThnA@mail.gmail.com> (raw)
In-Reply-To: <CAJZ5v0gSyPn8sZ2jJ+nZ_nu1Y=8+7Pg+pPvKGSijUm_sKitk4Q@mail.gmail.com>

On Mon, Jul 29, 2019 at 3:03 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
>
> On Mon, Jul 29, 2019 at 11:43 PM Saravana Kannan <saravanak@google.com> wrote:
> >
> > On Mon, Jul 29, 2019 at 2:25 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
> > >
> > > On Mon, Jul 29, 2019 at 10:47 PM Saravana Kannan <saravanak@google.com> wrote:
> > > >
> > > > Rafael,
> > > >
> > > > This is the fix you need. Or something link this.
> > > >
> > > > I had asked you to reject DL_FLAG_MANAGED as an input flag if you are
> > > > marking it as internal (in the comments). But looks like you were also
> > > > trying to check for "undefined" bit positions. However, the check
> > > > isn't correct because DL_MANAGED_FLAGS doesn't include (rightfully so)
> > > > DL_FLAG_PM_RUNTIME and DL_FLAG_RPM_ACTIVE .
> > > >
> > > > I tried to write a DL_FLAG_EXTERNAL to include all the external flags,
> > > > but that felt like a maintenance headache that's not worth carrying. I
> > > > think it's simpler to just error out when internal flags being passed
> > > > in and ignore any undefined bit positions.
> > >
> > > Well, IMO it is better to prevent people from passing unrecognized
> > > flags to device_link_add() at all, even if that means some extra
> > > effort when adding new flags.
> >
> > It isn't so much the extra effort that's a concern, but people might
> > miss updating whatever grouping macro we use.
> >
> > >
> > > I'll post an alternative fix shortly.
> >
> > You might want to move the MANAGED_FLAGs and other grouping macros
> > into the header file then? So that if someone is adding new flags,
> > it'll be less likely they'll forget to update the grouping macro?
>
> They would need to update device_link_add() itself, so updating a
> thing next to it does't seem to be so much of an issue.
>
> Moreover, the "grouping macro" is not relevant for any users of the
> API, just for device_link_add() itself, so I'm not sure how much
> better it is to have it in the header.
>
> And, of course, if anyone forgets to update the "grouping macro", they
> will find that the new flags are rejected immediately.

Sounds good.

-Saravana