linux-kernel - Re: [PATCH 1/5] of: introduce of_graph_get_remote

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Message-ID: <1486389834.3005.55.camel@pengutronix.de>
Date:   Mon, 06 Feb 2017 15:03:54 +0100
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Rob Herring <robh@...nel.org>
Cc:     David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Sean Paul <seanpaul@...omium.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Archit Taneja <architt@...eaurora.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Inki Dae <inki.dae@...sung.com>,
        Joonyoung Shim <jy0922.shim@...sung.com>,
        Seung-Woo Kim <sw0312.kim@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Kukjin Kim <kgene@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Javier Martinez Canillas <javier@....samsung.com>,
        Stefan Agner <stefan@...er.ch>,
        Alison Wang <alison.wang@...escale.com>,
        Xinliang Liu <z.liuxinliang@...ilicon.com>,
        Rongrong Zou <zourongrong@...il.com>,
        Xinwei Kong <kong.kongxinwei@...ilicon.com>,
        Chen Feng <puck.chen@...ilicon.com>,
        CK Hu <ck.hu@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Marek Vasut <marex@...x.de>,
        Mark Yao <mark.yao@...k-chips.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Liviu Dudau <liviu.dudau@....com>,
        Mali DP Maintainers <malidp@...s.arm.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Carlo Caione <carlo@...one.org>,
        Kevin Hilman <khilman@...libre.com>,
        Rob Clark <robdclark@...il.com>, Jyri Sarha <jsarha@...com>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Eric Anholt <eric@...olt.net>,
        Russell King <rmk+kernel@...linux.org.uk>
Subject: Re: [PATCH 1/5] of: introduce of_graph_get_remote_node

On Mon, 2017-02-06 at 07:54 -0600, Rob Herring wrote:
> On Mon, Feb 6, 2017 at 4:32 AM, Philipp Zabel <p.zabel@...gutronix.de> wrote:
> > Hi Rob,
> >
> > thanks for this clean-up series! I was not aware how far the duplication
> > has spread over time.
> >
> > On Fri, 2017-02-03 at 21:36 -0600, Rob Herring wrote:
> >> The OF graph API leaves too much of the graph walking to clients when
> >> in many cases the driver doesn't care about accessing the port or
> >> endpoint nodes. The drivers typically just want the device connected via
> >> a particular graph connection. of_graph_get_remote_node provides this
> >> functionality.
> >>
> >> Signed-off-by: Rob Herring <robh@...nel.org>
> >> ---
> >>  drivers/of/base.c        | 28 ++++++++++++++++++++++++++++
> >>  include/linux/of_graph.h |  8 ++++++++
> >>  2 files changed, 36 insertions(+)
> >>
> >> diff --git a/drivers/of/base.c b/drivers/of/base.c
> >> index d4bea3c797d6..ea18ab16b92c 100644
> >> --- a/drivers/of/base.c
> >> +++ b/drivers/of/base.c
> >> @@ -2469,3 +2469,31 @@ struct device_node *of_graph_get_remote_port(const struct device_node *node)
> >>       return of_get_next_parent(np);
> >>  }
> >>  EXPORT_SYMBOL(of_graph_get_remote_port);
> >> +
> >> +struct device_node *of_graph_get_remote_node(const struct device_node *node,
> >> +                                          int port, int endpoint)
> >
> > I think this should have a documentation comment, similar to the
> > of_graph_get_endpoint_by_regs one, as it is not really clear from the
> > function name that the returned device node is the parent (or
> > grandparent) device node containing the remote port to the specified
> > node & port & endpoint.
> > Also it might be interesting to the user that -1 is a wildcard value for
> > port / endpoint.
> 
> I really want to not allow using a wildcard here. Drivers should know
> what port they want (or iterate over all of them). It didn't look like
> any drivers were depending on the wildcard, but were just using -1 for
> "no reg property" when really that should 0. Of course, I may have
> missed something.
> 
> I guess I could enforce port/endpoint > 0 here as there's no existing users.

That sounds reasonable. If it works for all users, enforcing >= 0 should
be fine, but in that case I'd change the parameters to be unsigned.

regards
Philipp