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

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Date:	Wed, 2 Oct 2013 23:12:15 -0500
From:	Suman Anna <s-anna@...com>
To:	Mark Rutland <mark.rutland@....com>
CC:	Kumar Gala <galak@...eaurora.org>,
	Ohad Ben-Cohen <ohad@...ery.com>,
	Tony Lindgren <tony@...mide.com>,
	Benoit Cousson <bcousson@...libre.com>,
	Paul Walmsley <paul@...an.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCHv2 2/9] hwspinlock/omap: add support for dt nodes

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@...com>
>>> ---
>>> .../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.

> 
>>> +- 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.

> 
>>> +- 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.

> 
>>> +- 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.

Thanks
Suman
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