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

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Date:   Mon, 13 May 2019 09:13:11 +0000
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" <linux-remoteproc@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-stm32@...md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
CC:     Benjamin GAIGNARD <benjamin.gaignard@...com>,
        Fabien DESSENNE <fabien.dessenne@...com>
Subject: Re: [PATCH v2 0/6] hwspinlock: allow sharing of hwspinlocks

Hi


I Got Rob's Reviewed-by. Any further comments?


Fabien


On 25/04/2019 11:17 AM, 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@...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(-)
>