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
