Message-ID: <20250210100307.GA2966@pendragon.ideasonboard.com>
Date: Mon, 10 Feb 2025 12:03:07 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: "zhangzekun (A)" <zhangzekun11@...wei.com>
Cc: Oleksij Rempel <o.rempel@...gutronix.de>, robh@...nel.org,
	saravanak@...gle.com, justin.chen@...adcom.com,
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	cristian.marussi@....com, arm-scmi@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-media@...r.kernel.org,
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	chenjun102@...wei.com
Subject: Re: [PATCH 1/9] of: Add warpper function
 of_find_node_by_name_balanced()

Hi Zekun,

On Mon, Feb 10, 2025 at 02:47:28PM +0800, zhangzekun (A) wrote:
> > I think we all agree that of_find_node_by_name() is miused, and that it
> > shows the API isn't optimal. What we have different opinions on is how
> > to make the API less error-prone. I think adding a new
> > of_find_node_by_name_balanced() function works around the issue and
> > doesn't improve the situation much, I would argue it makes things even
> > more confusing.
> > 
> > We have only 20 calls to of_find_node_by_name() with a non-NULL first
> > argument in v6.14-rc1:
> > 
> > arch/powerpc/platforms/chrp/pci.c:      rtas = of_find_node_by_name (root, "rtas");
> > 
> > The 'root' variable here is the result of a call to
> > 'of_find_node_by_path("/")', so I think we could pass a null pointer
> > instead to simplify things.
> > 
> > arch/powerpc/platforms/powermac/pic.c:          slave = of_find_node_by_name(master, "mac-io");
> > 
> > Here I believe of_find_node_by_name() is called to find a *child* node
> > of 'master'. of_find_node_by_name() is the wrong function for that.
> > 
> > arch/sparc/kernel/leon_kernel.c:        np = of_find_node_by_name(rootnp, "GAISLER_IRQMP");
> > arch/sparc/kernel/leon_kernel.c:                np = of_find_node_by_name(rootnp, "01_00d");
> > arch/sparc/kernel/leon_kernel.c:        np = of_find_node_by_name(nnp, "GAISLER_GPTIMER");
> > arch/sparc/kernel/leon_kernel.c:                np = of_find_node_by_name(nnp, "01_011");
> > 
> > Here too the code seems to be looking for child nodes only (but I
> > couldn't find a DT example or binding in-tree, so I'm not entirely
> > sure).
> > 
> > drivers/clk/ti/clk.c:   return of_find_node_by_name(from, tmp);
> > 
> > Usage here seems correct, the reference-count decrement is intended.
> > 
> > drivers/media/i2c/max9286.c:    i2c_mux = of_find_node_by_name(dev->of_node, "i2c-mux");
> > drivers/media/platform/qcom/venus/core.c:       enp = of_find_node_by_name(dev->of_node, node_name);
> > drivers/net/dsa/bcm_sf2.c:      ports = of_find_node_by_name(dn, "ports");
> > drivers/net/dsa/hirschmann/hellcreek_ptp.c:     leds = of_find_node_by_name(hellcreek->dev->of_node, "leds");
> > drivers/net/ethernet/broadcom/asp2/bcmasp.c:    ports_node = of_find_node_by_name(dev->of_node, "ethernet-ports");
> > drivers/net/ethernet/marvell/prestera/prestera_main.c:  ports = of_find_node_by_name(sw->np, "ports");
> > drivers/net/pse-pd/tps23881.c:  channels_node = of_find_node_by_name(priv->np, "channels");
> > drivers/regulator/scmi-regulator.c:     np = of_find_node_by_name(handle->dev->of_node, "regulators");
> > drivers/regulator/tps6594-regulator.c:          np = of_find_node_by_name(tps->dev->of_node, multi_regs[multi].supply_name);
> > 
> > Incorrect usage, as far as I understand all those drivers are looking
> > for child nodes only.
> > 
> > drivers/of/unittest.c:          found = of_find_node_by_name(nd->overlay, "test-unittest16");
> > drivers/of/unittest.c:          found = of_find_node_by_name(nd->overlay, "test-unittest17");
> > drivers/of/unittest.c:          found = of_find_node_by_name(nd->overlay, "test-unittest18");
> > drivers/of/unittest.c:          found = of_find_node_by_name(nd->overlay, "test-unittest19");
> > 
> > Here too I think only child nodes are meant to be considered.
> > 
> > of_find_node_by_name() is very much misused as most callers want to find
> > child nodes, while of_find_node_by_name() will walk the whole DT from a
> > given starting point.
> > 
> > I think the right fix here is to
> > 
> > - Replace of_find_node_by_name(root, ...) with
> >    of_find_node_by_name(NULL, ...) in arch/powerpc/platforms/chrp/pci.c
> >    (if my understanding of the code is correct).
> 
> For arch/powerpc/platforms/chrp/pci.c, noticing that there is a comment 
> in setup_peg2():
>   /* keep the reference to the root node */
> 
> It might can not be convert to of_find_node_by_name(NULL, ...), and the 
> origin use of of_find_node_by_name() put the ref count which want to be 
> kept.

But the reference is dropped by of_find_node_by_name(). Unless I'm
missing something, dropping the lien

	struct device_node *root = of_find_node_by_path("/");

and changing

	rtas = of_find_node_by_name (root, "rtas");

to

	rtas = of_find_node_by_name (NULL, "rtas");

will not change the behaviour of the code.

> > 
> > - Replace of_find_node_by_name() with of_get_child_by_name() in callers
> >    that need to search immediate children only (I expected that to be the
> >    majority of the above call sites)
>
> Since there is no enough information about these DT nodes, it would take 
> time to prove if it is OK to make such convert.

It will take a bit of time, yes. I'm afraid time is needed to improve
things :-) In most cases, as DT bindings are available, it shouldn't be
very difficult.

> > 
> > - If there are other callers that need to find indirect children,
> >    introduce a new of_get_child_by_name_recursive() function.
> > 
> > At that point, the only remaining caller of of_find_node_by_name()
> > (beside its usage in the for_each_node_by_name() macro) will be
> > drivers/clk/ti/clk.c, which uses the function correctly.
> > 
> > I'm tempted to then rename of_find_node_by_name() to
> > __of_find_node_by_name() to indicate it's an internal function not meant
> > to be called except in special cases. It could all be renamed to
> > __of_find_next_node_by_name() to make its behaviour clearer.
> >
> 
> The actual code logic of of_find_node_by_name() is more suitable to be 
> used in a loop.So,rename of_find_node_by_name() to 
> __of_find_next_node_by_name() seems to be a good idea.

-- 
Regards,

Laurent Pinchart

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