Re: [PATCH v2 1/3] mfd: core: Make a best effort attempt to match devices with the correct of_nodes

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Hi,

Am 2020-06-24 08:41, schrieb Lee Jones:
On Tue, 23 Jun 2020, Frank Rowand wrote:

On 2020-06-11 14:10, Lee Jones wrote:
> Currently, when a child platform device (sometimes referred to as a
> sub-device) is registered via the Multi-Functional Device (MFD) API,
> the framework attempts to match the newly registered platform device
> with its associated Device Tree (OF) node.  Until now, the device has
> been allocated the first node found with an identical OF compatible
> string.  Unfortunately, if there are, say for example '3' devices
> which are to be handled by the same driver and therefore have the same
> compatible string, each of them will be allocated a pointer to the
> *first* node.

As you mentioned elsewhere in this thread, this series "fixes" the
problem related to the "stericsson,ab8500-pwm" compatible.

I know, I said I would drop discussion of that compatible, but bear
with me for a second.  :-)

The "problem" is that the devices for multiple mfd child nodes with
the same compatible value of "stericsson,ab8500-pwm" will all have
a pointer to the first child node.  At the moment the same child
of_node being used by more than one device does not cause any
incorrect behavior.

Just in case the driver for "stericsson,ab8500-pwm" is modified
in a way that the child of_node needs to be distinct for each
device, and that changes gets back ported, it would be useful
to have Fixes: tags for this patch series.

So, at your discretion (and I'll let you worry about the correct
Fixes: tag format), this series fixes:

bad76991d7847b7877ae797cc79745d82ffd9120 mfd: Register ab8500 devices using the newly DT:ed MFD API

This patch isn't actually broken.

The issue is the DTB, which [0] addresses.

[0]
https://lkml.kernel.org/lkml/20200622083432.1491715-1-lee.jones@xxxxxxxxxx/

Now, I'm confused; because this patch doesn't use the reg property
but a different node name. I'd actually prefer this for any MFD
driver which has multiple nodes of the same compatible string. See
my reasoning here [1]. But until now, no one has responded. Thus,
I'd rather see a OF_MFD_CELL_NAME() which matches the node name
instead of the OF_MFD_CELL_REG() macro.

This would also circumvent the fact that the unit-address has one
number space. Eg. it is not possible to have:

mfd {
  compatible = "mfd,compatible";

  gpio@0 {
    reg = <0>;
  };
  gpio@1 {
    reg = <1>;
  };
  pwm@0 {
    reg = <0>;
  };
};

Although Rob mentioned to maybe relax that, but I sill fail to see
the advantage to have an arbitrary reg property instead of a unique
node name.

[1] https://lore.kernel.org/linux-devicetree/0709f20bc61afb6656bc57312eb69f56@xxxxxxxx/

--
-michael



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