linux-kernel - [PATCH v2 0/6] hwspinlock: allow sharing of hwspinlocks

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Date:   Thu, 25 Apr 2019 11:17:17 +0200
From:   Fabien Dessenne <fabien.dessenne@...com>
To:     Ohad Ben-Cohen <ohad@...ery.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Jonathan Corbet <corbet@....net>,
        <linux-remoteproc@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>, <linux-doc@...r.kernel.org>
CC:     Fabien Dessenne <fabien.dessenne@...com>,
        Benjamin Gaignard <benjamin.gaignard@...com>
Subject: [PATCH v2 0/6] hwspinlock: allow sharing of hwspinlocks

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@...0d000 {
		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.

Changes since v1:
* Removed useless 'status = "okay"' from stm32mp157c.dtsi

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                 |  9 +++
 drivers/hwspinlock/hwspinlock_core.c               | 82 +++++++++++++++++-----
 drivers/hwspinlock/hwspinlock_internal.h           |  2 +
 7 files changed, 107 insertions(+), 31 deletions(-)

-- 
2.7.4