Re: [Openipmi-developer] [patch 1/1] ipmi: add autosensing of ipmi device on powerpc using device-tree

[Arnd Bergmann <arnd@arndb.de>]

On Friday 08 December 2006 23:50, Benjamin Herrenschmidt wrote:
>=20
> >=20
> > +=A0=A0=A0=A0=A0info->io.regsize=A0=A0=A0=A0=A0=A0=A0=A0=3D resource0.e=
nd - resource0.start + 1;
> > +=A0=A0=A0=A0=A0info->io.regspacing=A0=A0=A0=A0=A0=3D resource1.start -=
 resource0.start;
> >=20
> > Are you sure this is a reliable way to check the register spacing and
> > register size? =A0Register size means "how big is a register (8, 16, 32
> > bits)". =A0Register spacing means (how many bytes are there between
> > registers. =A0If you had two registers that were 8 bits and 4 bytes
> > apart, for instance, I don't believe the above calculations would work.
>=20
> How many registers do we expect here ? Might be better to have one
> resource represent the whole MMIO area, and have a separate property
> that indicates the stride between 2 registers.

I think the current representation is perfect. AFAICS, there are always
two registers, but depending on the HW implementation, they may be
between 1 and 4 bytes wide, and can have a different spacing.

By having two separate areas in the reg property, the driver can
easily determine both the size and the spacing. It will then do
a single ioremap that spans both anyway.

	Arnd <><