Re: Regarding recently Added TPM2.0 support to the Nuvoton i2c driver

[George Wilson <ltcgcw-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

On Wed, Jul 27, 2016 at 11:42:29AM -0600, Jason Gunthorpe wrote:
> > Should not the device tree tell you what is actually *there* and let the
> > driver code decide what is compatible?  Rather than the firmware trying to
> > make a guess as to which Nuvoton device id to try to match in the Nuvoton
> > driver code?
> 
> Yes, that is what I suggested:
> 
> > >>>   compatible = "nuvoton,npct650", "nuvoton,npct601"
> 
> Today's kernel has no idea what 650 is, but since the DT says it is
> compatible with the 601 then today's kernel will bind to it. 601 is
> the kernel documented compatible tag for that specific I2C
> API.

So in this case, early firmware would simply pass the additional
compatible string.

> Perhaps we should add 6xx as the generic flavor? I'm not as clear on
> what DT maintainers think about that, but there is precedent.

We thought about suggesting that too.  However,
http://elinux.org/Device_Tree_Usage advises:

  Warning: Don't use wildcard compatible values, like
  "fsl,mpc83xx-uart" or similar. Silicon vendors will invariably
  make a change that breaks your wildcard assumptions the moment
  it is too late to change it. Instead, choose a specific silicon
  implementations and make all subsequent silicon compatible with
  it.

It looks like the driver's compatible table is on the right track and
we need to make our platform's device tree conform to its expectations.

-- 
George Wilson
IBM Linux Technology Center
Security Development


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