[PATCH 3/5] ARM: vexpress: Add DT support in v2m

[dave.martin@linaro.org (Dave Martin)]

On Wed, Nov 16, 2011 at 04:35:15PM +0000, Pawel Moll wrote:

[...]

> > > +  - for Coretile Express A5x2 (V2P-CA5s):
> > > +	compatible = "arm,vexpress-v2p-ca5s", "arm-vexpress";
> > > +  - Coretile Express A9x4 (V2P-CA9):
> > > +	comaptible = "arm,vexpress-v2p-ca9", "arm,vexpress-legacy", "arm-vexpress";
> > > +
> > > +Current Linux implementation requires a "timer" alias pointing
> > > +at a SP804 timer block to be used when tile is not using local
> > > +timer source.
> > 
> > We should specify a list of all the "standard" aliases used by the
> > generic motherboard code here, since these are part of the contract
> > between each board-specific device tree and the motherboard code.
> > 
> > Is "timer" the only one, or are there others?
> 
> One and only. There were more, but I got rid of them.

Are the other alises still used?  If not, we should perhaps get rid of
them, or keep them on an as-needed basis only?

Since alises are by definition a point of standardisation (otherwise
there's no need for an alias) I think they need to be documented alongside
bindings wherever we have them.

> > > diff --git a/arch/arm/mach-vexpress/Kconfig b/arch/arm/mach-vexpress/Kconfig
> > > index 9311484..4c11e90 100644
> > > --- a/arch/arm/mach-vexpress/Kconfig
> > > +++ b/arch/arm/mach-vexpress/Kconfig
> > > @@ -9,4 +9,8 @@ config ARCH_VEXPRESS_CA9X4
> > >  	select ARM_ERRATA_751472
> > >  	select ARM_ERRATA_753970
> > >  
> > 
> > For "non-interactive" config items, can we still please have comments
> > indicating what the item means and how it should be used?
> > 
> > Such comments can be very brief, but having at least something makes the
> > configs easier to understand and maintain, in my view.
> 
> Em, what bits do you refer to? The lines you quoted are not changed...

Hmmm, editing snafu there.

I think I was referring to the ARCH_VEXPRESS_DT item, which is defined
just after the lines I quoted.

> 
> > > diff --git a/arch/arm/mach-vexpress/v2m.c b/arch/arm/mach-vexpress/v2m.c
> > 
> > [...]
> > 
> > > +void __init v2m_dt_init_early(void)
> > > +{
> > > +	struct device_node *node;
> > > +	const __be32 *reg;
> > > +	u32 dt_hbi;
> > > +
> > > +	node = of_find_compatible_node(NULL, NULL, "arm,vexpress-sysreg");
> > > +	BUG_ON(!node);
> > > +	/* The following will become of_iomap() when possible */
> > > +	reg = of_get_property(node, "reg", NULL);
> > > +	BUG_ON(!reg);
> > > +	v2m_sysreg_base = V2M_PERIPH_P2V(be32_to_cpup(reg));
> > > +
> > > +	/* Confirm board type against DT property, if available */
> > > +	if (of_property_read_u32(allnodes, "arm,hbi", &dt_hbi) == 0) {
> > > +		u32 misc = readl(v2m_sysreg_base + V2M_SYS_MISC);
> > > +		u32 id = readl(v2m_sysreg_base + (misc & SYS_MISC_MASTERSITE ?
> > > +				V2M_SYS_PROCID1 : V2M_SYS_PROCID0));
> > > +		u32 hbi = id & SYS_PROCIDx_HBI_MASK;
> > > +
> > > +		if (WARN_ON(dt_hbi != hbi))
> > > +			pr_warning("vexpress: DT HBI (%x) is not matching "
> > > +					"hardware (%x)!\n", dt_hbi, hbi);
> > 
> > Once this code is mature enough, should we panic the kernel here
> > instead?
> 
> I'm not convinced. Actually the first version I wrote was panicking. But
> then I thought that if it works, it works - why should I prevent this?
> The use case is simple - FPGA implementations, being
> mostly-exact-equivalents of the core tiles, will have the logic tile HBI
> here. And to use them you would have to modify the DTS if this code
> panicked. With WARN_ON you'll see the message, but if you know what are
> you doing, that's fine...
> 
> Don't know, really. Any strong feelings about it?

I don't have a strong feeling about it.  Printing a warning is certainly
helpful; by definition we don't really know what to do beyond this
point.

So, the choices are: try to do something reasonable, or panic.

There's no right answer.  "Try to do something reasonable" seems as good
as any other option ... and there's always the possibility that it might
work.

Cheers
---Dave