[PATCH] i2c: mux: Fix the crash when the i2c-arbitrator node is present

[Abbarapu, Venkatesh]

[AMD Official Use Only - AMD Internal Distribution Only]

Hi Heiko,


> -----Original Message-----
> From: Heiko Schocher <hs at denx.de>
> Sent: Wednesday, May 28, 2025 3:05 PM
> To: Abbarapu, Venkatesh <venkatesh.abbarapu at amd.com>; u-boot at lists.denx.de;
> Simon Glass <sjg at chromium.org>
> Cc: Simek, Michal <michal.simek at amd.com>; trini at konsulko.com; git (AMD-Xilinx)
> <git at amd.com>
> Subject: Re: [PATCH] i2c: mux: Fix the crash when the i2c-arbitrator node is present
>
> Hello Venkatesh,
>
> On 28.05.25 05:12, Venkatesh Yadav Abbarapu wrote:
> > Observing the crash when we add the i2c-arbitrator node in the device
>
> Which crash?

Observing crash like below
U-Boot 2025.01 (May 22 2025 - 12:32:01 +0000)
CPU:   ZynqMP
Silicon: v3
Chip:  xck24
Model: ZynqMP SC K24 RevA
Board: Xilinx ZynqMP
DRAM:  2 GiB
initcall failed at call 0000000008037364 (err=-22)
### ERROR ### Please RESET the board ###


>
> > tree as per the DT bindings. The issue is with the child node of
> > i2c-arbitrator at 72 i.e., i2c at f1950000->i2c-arbitrator at 72->i2c-arb, as
> > the arbitrator uses the uclass of mux(UCLASS_I2C_MUX) and the mux
> > uclass driver checks for the "reg" property using the
> > i2c_mux_child_post_bind() function, if it won't find the "reg"
> > property it will return -EINVAL which is leading to the crash.
> > So, add the logic to check whether the  child node has the "reg"
> > property, if the "reg" property exists then read the "reg" and update the channel.
> >
> > https://www.kernel.org/doc/Documentation/devicetree/bindings/i2c/i2c-a
> > rb.txt
> >
> > Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu at amd.com>
> > ---
> >   drivers/i2c/muxes/i2c-mux-uclass.c | 11 +++++++----
> >   1 file changed, 7 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/i2c/muxes/i2c-mux-uclass.c
> > b/drivers/i2c/muxes/i2c-mux-uclass.c
> > index d1999d21feb..b18999c1fe3 100644
> > --- a/drivers/i2c/muxes/i2c-mux-uclass.c
> > +++ b/drivers/i2c/muxes/i2c-mux-uclass.c
> > @@ -40,11 +40,14 @@ static int i2c_mux_child_post_bind(struct udevice *dev)
> >     struct i2c_mux_bus *plat = dev_get_parent_plat(dev);
> >     int channel;
> >
> > -   channel = dev_read_u32_default(dev, "reg", -1);
>
> Shouldn;t this function return -1 (the default value), if property "reg" is not present?
> (And also if dev_ofnode(dev) is not valid?)
>
> Seems we should look into this function and may fix the problem there?
>
> Aha, this comes from
>
> drivers/core/read.c
> int dev_read_u32_default(const struct udevice *dev, const char *propname,
>                           int def)
> {
>          return ofnode_read_u32_default(dev_ofnode(dev), propname, def); }
>
> with drivers/core/ofnode.c
> u32 ofnode_read_u32_default(ofnode node, const char *propname, u32 def) {
>          assert(ofnode_valid(node));
>          ofnode_read_u32_index(node, propname, 0, &def);
>
>          return def;
> }
>
> added Simon.
>
> @Simon: may proper fix would be to check in ofnode_read_u32_default()
>          if propname exists, and if not return default value?
>          May also return with default value if node is not valid?
>
>          What do you think?
>
>          Thanks!
>
>
> > -   if (channel < 0)
> > -           return -EINVAL;
> > -   plat->channel = channel;
> > +   ofnode node = dev_ofnode(dev);
> >
> > +   if (ofnode_has_property(node, "reg")) {
>
> If we fix it in this code, you can here simply return immediately if "reg" propertyis
> missing, so you can save the identation level, and patch looks cleaner.
>
> > +           channel = dev_read_u32_default(dev, "reg", -1);
> > +           if (channel < 0)
> > +                   return -EINVAL;
> > +           plat->channel = channel;
> > +   }
> >     return 0;
> >   }
> >
> >
>
> Thanks!

Thanks
Venkatesh
>
> bye,
> Heiko
> --
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