Re: [PATCHv2 2/9] hwspinlock/omap: add support for dt nodes

[Mark Rutland]

On Thu, Oct 03, 2013 at 05:12:15AM +0100, Suman Anna wrote:
> Hi Mark,
> 
> > On Fri, Sep 27, 2013 at 05:06:38PM +0100, Kumar Gala wrote:
> >>
> >> On Sep 17, 2013, at 2:30 PM, Suman Anna wrote:
> >>
> >>> HwSpinlock IP is present only on OMAP4 and other newer SoCs,
> >>> which are all device-tree boot only. This patch adds the
> >>> base support for parsing the DT nodes, and removes the code
> >>> dealing with the traditional platform device instantiation.
> >>>
> >>> Signed-off-by: Suman Anna <s-anna@xxxxxx>
> >>> ---
> >>> .../devicetree/bindings/hwlock/omap-hwspinlock.txt | 31 +++++++++++
> >>> arch/arm/mach-omap2/Makefile                       |  3 --
> >>> arch/arm/mach-omap2/hwspinlock.c                   | 60 ----------------------
> >>> drivers/hwspinlock/omap_hwspinlock.c               | 23 +++++++--
> >>> 4 files changed, 50 insertions(+), 67 deletions(-)
> >>> create mode 100644 Documentation/devicetree/bindings/hwlock/omap-hwspinlock.txt
> >>> delete mode 100644 arch/arm/mach-omap2/hwspinlock.c
> >>>
> >>> diff --git a/Documentation/devicetree/bindings/hwlock/omap-hwspinlock.txt b/Documentation/devicetree/bindings/hwlock/omap-hwspinlock.txt
> >>> new file mode 100644
> >>> index 0000000..235b7c5
> >>> --- /dev/null
> >>> +++ b/Documentation/devicetree/bindings/hwlock/omap-hwspinlock.txt
> >>> @@ -0,0 +1,31 @@
> >>> +OMAP4+ HwSpinlock Driver
> >>> +========================
> >>> +
> >>> +Required properties:
> >>> +- compatible:		Currently supports only "ti,omap4-hwspinlock" for
> >>> +				OMAP44xx, OMAP54xx, AM33xx, AM43xx, DRA7xx SoCs
> > 
> > "Currently supports" is not something I expect to see in a binding
> > document. That sounds like a description of the driver rather than the
> > binding.
> > 
> > How similar are these hardware modules? What are the differences?
> 
> The IP is almost the same, they all have the same revision id. The
> number of locks (each represented by a register) though vary from one
> SoC to another (OMAP4, OMAP5, DRA7 have same number of locks, and
> AM33xx/AM43xx have a different number). The number of locks is directly
> read by the driver from a module register. There is no separate .data
> associated with the of_device_id table, so I used a single compatible
> property for all the SoCs.

Ok. Probeability is good, it keeps these simpler :)

I think This can be reworded to say "should contain" rather than "currently
supports only":

- compatible:		Should contain "ti,omap4-hwspinlock" for
			OMAP44xx, OMAP54xx, AM33xx, AM43xx, or DRA7xx SoCs

That way the binding allows for a future backwards-compatible variant, and
doesn't mention the current level of support in Linux.

> 
> > 
> >>> +- reg:			Contains the hwspinlock register address range (base
> >>> +			address and length)
> > 
> > Is there only one register bank for the hwlock module?
> 
> The lock registers start at a certain offset (0x800) within the module
> register space, and the offsets for various registers are identical
> between all SoCs.

What are the other registers within the module? Are they shared with other
devices, or are they simply unused by the hwspinlock driver?

> 
> > 
> >>> +- ti,hwmods:		Name of the hwmod associated with the hwspinlock device
> >>> +
> >>> +Common hwlock properties:
> >>> +The following describes the usage of the common hwlock properties (defined in
> >>> +Documentation/devicetree/bindings/hwlock/hwlock.txt) on OMAP.
> >>> +
> >>> +- hwlock-base-id:	There are currently no OMAP SoCs with multiple
> >>> +			hwspinlock devices. The OMAP driver uses a default
> >>> +			base id value of 0 for the locks present within the
> >>> +			single hwspinlock device on all SoCs.
> > 
> > 
> > Driver details should not leak into bindngs...
> 
> OK, will remove the info on driver details.
> 
> > 
> > As mentioned in the other patch, I don't think this is the way to handle
> > this. I think we need a phandle + args representation.
> 
> This is an optional parameter for now and I was going to revise the
> description based on comments from Kumar Gala on this thread, but I will
> wait and adjust this based on the outcome on the first patch.

Ok.

> 
> > 
> >>> +- hwlock-num-locks:	This property is not required on OMAP SoCs, since the
> >>> +			number of locks present within a device can be deduced
> >>> +			from the SPINLOCK_SYSSTATUS device register.
> > 
> > Huh? Why define this property at all here if we don't need it and don't
> > use it?
> > 
> > The common document should state that specific bindings may use it and
> > should explicitly state if they do, rather than stating they don't...
> 
> Yeah, I wasn't sure how to go about the split between the common file
> and the platform-specific bindings. I will clean this up and revise the
> common bindings.

Ok.

Cheers,
Mark.
> 
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