Re: CPU revision IDs

[Maxime Ripard <maxime.ripard-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>]

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On Fri, Jun 13, 2014 at 10:37:37AM -0400, jonsmirl-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org wrote:
> >> Then I end up with code in the machine file like this...
> >>
> >> find SOC revision
> >> if revision == A
> >>     fix up codec and i2s driver compatible
> >> if revision == B
> >>     fix up HDMI compatible
> >> if revision == C
> >>     fix up whatever
> >> I've seen chips with revision levels of J
> >>
> >> Why do you want this knowledge in the machine file? Why not just add
> >> the test for SOC revision inside the device driver?
> >
> > Because it's going to be a mess anyway. No matter if it's in the
> > driver or the machine code. So at least, that way, we're having it
> > centralized and isolated from the driver's code.
> 
> The mess is always going to be in the driver code. You are just
> changing the the string the driver code selects on...
> 
> if (of_machine_is_compatible("allwinner,sun7i-codec-rev-a")) {
>       fix bug
> }
> 
> if (of_machine_is_compatible("allwinner,sun7i-a20a")) {
>       fix bug
> }

What? Hmmm, nope. Look at how we're doing this for the i2c driver
(drivers/i2c/busses/i2c-mv64xxx.c).

> The mess is not required in the machine file.  Init time code can
> always modify the machine compatible string like this with no side
> effects. It would add 'a'-'j' as appropriate for the CPU.
> 
> Code changes this:
>  compatible = "cubietech,cubietruck", "allwinner,sun7i-a20"
> to:
>  compatible = "cubietech,cubietruck",  "allwinner,sun7i-a20-a",
> "allwinner,sun7i-a20"

Again, this is the machine compatible, and this is orthogonal to the
issue. You should have a different compatible string for the *codec*.

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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