Re: [RFC PATCH 3/5] i2c: core: add function to request an alias

[Wolfram Sang <wsa@the-dreams.de>]

[-- Attachment #1: Type: text/plain, Size: 1458 bytes --]


> > > As I said to Laurent, too, I think the risk that a bus is not fully
> > > described is higher than a device which does not respond to a read_byte.
> > > In both cases, we would wrongly use an address in use.
> 
> I don't fully agree with this, I think we shouldn't impose a penalty on
> every user because some device trees don't fully describe the hardware.

I haven't decided yet. However, my general preference is that for a
generic OS like Linux, saftey comes first, then performance. If you have
a fully described DT, then the overhead will be 1 read_byte transaction
per requested alias at probe time. We could talk about using quick_read
to half the overhead. You could even patch it away, if it is too much
for $customer.

> I think we should, at the very least, skip the probe and rely on DT if
> DT explicitly states that all used addresses are listed. We discussed a
> property to report addresses used by devices not described in DT, if
> that property is listed I would prefer trusting DT.

Yeah, we discussed this property and I have no intentions of dropping
it. I haven't though of including it into this series, but it probably
makes sense. We don't have to define much anyhow, just state what
already exists, I guess.

From Documentation/devicetree/bindings/i2c/i2c-ocores.txt:

	dummy@60 {
		compatible = "dummy";
		reg = <0x60>;
	};

I think "dummy" is generic enough to be described in i2c.txt.


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]