On Wed 13 Mar 08:50 PDT 2019, Fabien Dessenne wrote:

The current implementation does not allow two different devices to use
a common hwspinlock. This patch set proposes to have, as an option, some
hwspinlocks shared between several users.

Below is an example that explain the need for this:
	exti: interrupt-controller@5000d000 {
		compatible = "st,stm32mp1-exti", "syscon";
		interrupt-controller;
		#interrupt-cells = <2>;
		reg = <0x5000d000 0x400>;
		hwlocks = <&hsem 1>;
	};
The two drivers (stm32mp1-exti and syscon) refer to the same hwlock.
With the current hwspinlock implementation, only the first driver succeeds
in requesting (hwspin_lock_request_specific) the hwlock. The second request
fails.


The proposed approach does not modify the API, but extends the DT 'hwlocks'
property with a second optional parameter (the first one identifies an
hwlock) that specifies whether an hwlock is requested for exclusive usage
(current behavior) or can be shared between several users.
Examples:
	hwlocks = <&hsem 8>;	Ref to hwlock #8 for exclusive usage
	hwlocks = <&hsem 8 0>;	Ref to hwlock #8 for exclusive (0) usage
	hwlocks = <&hsem 8 1>;	Ref to hwlock #8 for shared (1) usage

As a constraint, the #hwlock-cells value must be 1 or 2.
In the current implementation, this can have theorically any value but:
- all of the exisiting drivers use the same value : 1.
- the framework supports only one value : 1 (see implementation of
  of_hwspin_lock_simple_xlate())
Hence, it shall not be a problem to restrict this value to 1 or 2 since
it won't break any driver.

Hi Fabien,

Your series looks good, but it makes me wonder why the hardware locks
should be an exclusive resource.

How about just making all (specific) locks shared?

Regards,
Bjorn

Fabien Dessenne (6):
  dt-bindings: hwlock: add support of shared locks
  hwspinlock: allow sharing of hwspinlocks
  dt-bindings: hwlock: update STM32 #hwlock-cells value
  ARM: dts: stm32: Add hwspinlock node for stm32mp157 SoC
  ARM: dts: stm32: Add hwlock for irqchip on stm32mp157
  ARM: dts: stm32: hwlocks for GPIO for stm32mp157

 .../devicetree/bindings/hwlock/hwlock.txt          | 27 +++++--
 .../bindings/hwlock/st,stm32-hwspinlock.txt        |  6 +-
 Documentation/hwspinlock.txt                       | 10 ++-
 arch/arm/boot/dts/stm32mp157-pinctrl.dtsi          |  2 +
 arch/arm/boot/dts/stm32mp157c.dtsi                 | 10 +++
 drivers/hwspinlock/hwspinlock_core.c               | 82 +++++++++++++++++-----
 drivers/hwspinlock/hwspinlock_internal.h           |  2 +
 7 files changed, 108 insertions(+), 31 deletions(-)

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2.7.4