Re: [PATCH V4 2/4] DRIVERS: IRQCHIP: CROSSBAR: Add support for Crossbar IP

[Mark Rutland <mark.rutland@arm.com>]

On Thu, Nov 14, 2013 at 04:41:41PM +0000, Sricharan R wrote:
> Hi Mark,
> 
> On Thursday 14 November 2013 07:42 PM, Mark Rutland wrote:
> > On Thu, Nov 14, 2013 at 12:18:48PM +0000, Sricharan R wrote:
> >> Some socs have a large number of interrupts requests to service
> >> the needs of its many peripherals and subsystems. All of the
> >> interrupt lines from the subsystems are not needed at the same
> >> time, so they have to be muxed to the irq-controller appropriately.
> >> In such places a interrupt controllers are preceded by an CROSSBAR
> >> that provides flexibility in muxing the device requests to the controller
> >> inputs.
> >>
> >> This driver takes care a allocating a free irq and then configuring the
> >> crossbar IP as a part of the mpu's irqchip callbacks. crossbar_init should
> >> be called right before the irqchip_init, so that it is setup to handle the
> >> irqchip callbacks.
> >>
> >> Cc: Thomas Gleixner <tglx@linutronix.de>
> >> Cc: Linus Walleij <linus.walleij@linaro.org>
> >> Cc: Santosh Shilimkar <santosh.shilimkar@ti.com>
> >> Cc: Russell King <linux@arm.linux.org.uk>
> >> Cc: Tony Lindgren <tony@atomide.com>
> >> Cc: Rajendra Nayak <rnayak@ti.com>
> >> Cc: Marc Zyngier <marc.zyngier@arm.com>
> >> Cc: Grant Likely <grant.likely@linaro.org>
> >> Cc: Rob Herring <rob.herring@calxeda.com>
> >> Signed-off-by: Sricharan R <r.sricharan@ti.com>
> >> Acked-by: Kumar Gala <galak@codeaurora.org> (for DT binding portion)
> >> Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
> >> ---
> >>  [V2] Addressed Thomas Gleixner <tglx@linutronix.de> comments
> >>       and renamed the bindings as per Kumar Gala <galak@codeaurora.org>
> >>       comments.
> >>  [V3] Changed static inline const to static inline int and removed
> >>       unnecessary variable initialization as per
> >>       Thomas Gleixner <tglx@linutronix.de>. Updated commit tags
> >>  [V4] Renamed crossbar_init as irqcrossbar_init as per
> >>       Rajendra Nayak <rnayak@ti.com> suggestion.
> >>
> >>  .../devicetree/bindings/arm/omap/crossbar.txt      |   27 +++
> >>  drivers/irqchip/Kconfig                            |    8 +
> >>  drivers/irqchip/Makefile                           |    1 +
> >>  drivers/irqchip/irq-crossbar.c                     |  206 ++++++++++++++++++++
> >>  include/linux/irqchip/irq-crossbar.h               |   11 ++
> >>  5 files changed, 253 insertions(+)
> >>  create mode 100644 Documentation/devicetree/bindings/arm/omap/crossbar.txt
> >>  create mode 100644 drivers/irqchip/irq-crossbar.c
> >>  create mode 100644 include/linux/irqchip/irq-crossbar.h
> >>
> >> diff --git a/Documentation/devicetree/bindings/arm/omap/crossbar.txt b/Documentation/devicetree/bindings/arm/omap/crossbar.txt
> >> new file mode 100644
> >> index 0000000..fb88585
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/arm/omap/crossbar.txt
> >> @@ -0,0 +1,27 @@
> >> +Some socs have a large number of interrupts requests to service
> >> +the needs of its many peripherals and subsystems. All of the
> >> +interrupt lines from the subsystems are not needed at the same
> >> +time, so they have to be muxed to the irq-controller appropriately.
> >> +In such places a interrupt controllers are preceded by an CROSSBAR
> >> +that provides flexibility in muxing the device requests to the controller
> >> +inputs.
> >> +
> >> +Required properties:
> >> +- compatible : Should be "ti,irq-crossbar"
> >> +- reg: Base address and the size of the crossbar registers.
> >> +- ti,max-irqs: Total number of irqs available at the interrupt controller.
> >> +- ti,reg-size: Size of a individual register in bytes. Every individual
> >> +	    register is assumed to be of same size. Valid sizes are 1, 2, 4.
> >> +- ti,irqs-reserved: List of the reserved irq lines that are not muxed using
> >> +		 crossbar. These interrupt lines are reserved in the soc,
> >> +		 so crossbar bar driver should not consider them as free
> >> +		 lines.
> > The combination of the ti,max-irqs and ti,irqs-reserved properties seems
> > backwards to me. Why can we not describe the set of IRQs that _can_ be
> > used?
>  Total set of irqs that are usable is max - reserved. Since reserved irqs
>  are not continuous, we have to give the list. During the init we count
>  the total number of reserved and get the usable one.

So why not describe the set of usable IRQs, rather than a set of IRQs
for which only some are usable then subtracting the set of unusable
IRQs?

It seems backwards to me to have a binding for a device describe
resources it doesn't have.

> >> +
> >> +Examples:
> >> +		crossbar_mpu: @4a020000 {
> >> +			compatible = "ti,irq-crossbar";
> >> +			reg = <0x4a002a48 0x130>;
> >> +			ti,max-irqs = <160>;
> >> +			ti,reg-size = <2>;
> >> +			ti,irqs-reserved = <0 1 2 3 5 6 131 132 139 140>;
> >> +		};
> > [...]
> >
> >> +	/* Get and mark reserved irqs */
> >> +	irqsr = of_get_property(node, "ti,irqs-reserved", &size);
> >> +	if (irqsr) {
> >> +		size /= sizeof(__be32);
> >> +
> >> +		for (i = 0; i < size; i++) {
> >> +			entry = be32_to_cpup(irqsr + i);
> >> +			if (entry > max) {
> >> +				pr_err("Invalid reserved entry\n");
> >> +				goto err3;
> >> +			}
> >> +			cb->irq_map[entry] = 0;
> >> +		}
> >> +	}
> > Don't deal with the raw DTB. Use of_property_read_u32_index.
>  Ok, i will correct this.
> >> +
> >> +	cb->register_offsets = kzalloc(max * sizeof(int), GFP_KERNEL);
> >> +	if (!cb->register_offsets)
> >> +		goto err3;
> >> +
> >> +	of_property_read_u32(node, "ti,reg-size", &size);
> > If "ti,reg-size" isn't present, size is uninitialized. Please check the
> > return value of of_property_read_u32.
> Ok, will correct this.

Cheers.

Mark.