Re: [PATCH 01/11] firmware: arm_scmi: review protocol registration interface

From: Cristian Marussi <cristian.marussi@arm.com>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
	LAK <linux-arm-kernel@lists.infradead.org>,
	Sudeep Holla <sudeep.holla@arm.com>,
	Lukasz Luba <lukasz.luba@arm.com>,
	james.quinlan@broadcom.com,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	f.fainelli@gmail.com,
	Etienne Carriere <etienne.carriere@linaro.org>,
	Thara Gopinath <thara.gopinath@linaro.org>,
	Souvik Chakravarty <souvik.chakravarty@arm.com>
Subject: Re: [PATCH 01/11] firmware: arm_scmi: review protocol registration interface
Date: Thu, 15 Oct 2020 10:58:30 +0100	[thread overview]
Message-ID: <20201015095830.GC34395@e120937-lin> (raw)
In-Reply-To: <CAKfTPtCGQm14JcAn-Lb0o5yTjMrnPA59LcnC+L5WMwX6gTdm5w@mail.gmail.com>

Hi Vincent,

thanks for the review.

On Thu, Oct 15, 2020 at 11:41:09AM +0200, Vincent Guittot wrote:
> On Wed, 14 Oct 2020 at 17:06, Cristian Marussi <cristian.marussi@arm.com> wrote:
> >
> > Extend common protocol registration routines and provide some new generic
> > protocols' init/deinit helpers that tracks protocols' users and automatically
> > perform the proper initialization/de-initialization on demand.
> >
> > Convert all protocols to use new registration schema while modifying only Base
> > protocol to use also the new initialization helpers.
> >
> > All other standard protocols' initialization is still umodified and bound to
> > SCMI devices probing.
> >
> > Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
> > ---
> 
> [...]
> 
> >
> > +/**
> > + * scmi_get_protocol_instance  - Protocol initialization helper.
> > + * @handle: A reference to the SCMI platform instance.
> > + * @protocol_id: The protocol being requested.
> > + *
> > + * In case the required protocol has never been requested before for this
> > + * instance, allocate and initialize all the needed structures while handling
> > + * resource allocation with a dedicated per-protocol devres subgroup.
> > + *
> > + * Return: A reference to an initialized protocol instance or error on failure.
> > + */
> > +static struct scmi_protocol_instance * __must_check
> > +scmi_get_protocol_instance(struct scmi_handle *handle, u8 protocol_id)
> > +{
> > +       int ret = -ENOMEM;
> > +       void *gid;
> > +       struct scmi_protocol_instance *pi;
> > +       struct scmi_info *info = handle_to_scmi_info(handle);
> > +
> > +       mutex_lock(&info->protocols_mtx);
> > +       /* Ensure protocols has been updated */
> > +       smp_rmb();
> 
> Why do you need this smp_rmb and the smp_wmb below ?
> 
> Isn't the mutex not enough ?
> 

You're right, it's a leftover I think, since initially there was no
mutex. I'll remove it in V2.

Thanks

Cristian

> > +       pi = info->protocols[protocol_id];
> > +
> > +       if (!pi) {
> > +               const struct scmi_protocol *proto;
> > +
> > +               /* Fail if protocol not registered on bus */
> > +               proto = scmi_get_protocol(protocol_id);
> > +               if (!proto) {
> > +                       ret = -EINVAL;
> > +                       goto out;
> > +               }
> > +
> > +               /* Protocol specific devres group */
> > +               gid = devres_open_group(handle->dev, NULL, GFP_KERNEL);
> > +               if (!gid)
> > +                       goto out;
> > +
> > +               pi = devm_kzalloc(handle->dev, sizeof(*pi), GFP_KERNEL);
> > +               if (!pi)
> > +                       goto clean;
> > +
> > +               pi->gid = gid;
> > +               pi->proto = proto;
> > +               refcount_set(&pi->users, 1);
> > +               /* proto->init is assured NON NULL by scmi_protocol_register */
> > +               ret = pi->proto->init(handle);
> > +               if (ret)
> > +                       goto clean;
> > +
> > +               info->protocols[protocol_id] = pi;
> > +               /* Ensure initialized protocol is visible */
> > +               smp_wmb();
> > +
> > +               devres_close_group(handle->dev, pi->gid);
> > +               dev_dbg(handle->dev, "Initialized protocol: 0x%X\n",
> > +                       protocol_id);
> > +       } else {
> > +               refcount_inc(&pi->users);
> > +       }
> > +       mutex_unlock(&info->protocols_mtx);
> > +
> > +       return pi;
> > +
> > +clean:
> > +       devres_release_group(handle->dev, gid);
> > +out:
> > +       mutex_unlock(&info->protocols_mtx);
> > +       return ERR_PTR(ret);
> > +}
> > +
> > +/**
> > + * scmi_acquire_protocol  - Protocol acquire
> > + * @handle: A reference to the SCMI platform instance.
> > + * @protocol_id: The protocol being requested.
> > + *
> > + * Register a new user for the requested protocol on the specified SCMI
> > + * platform instance, possibly triggering its initialization on first user.
> > + *
> > + * Return: 0 if protocol was acquired successfully.
> > + */
> > +int scmi_acquire_protocol(struct scmi_handle *handle, u8 protocol_id)
> > +{
> > +       return IS_ERR(scmi_get_protocol_instance(handle, protocol_id));
> > +}
> > +
> > +/**
> > + * scmi_release_protocol  - Protocol de-initialization helper.
> > + * @handle: A reference to the SCMI platform instance.
> > + * @protocol_id: The protocol being requested.
> > + *
> > + * Remove one user for the specified protocol and triggers de-initialization
> > + * and resources de-allocation once the last user has gone.
> > + */
> > +void scmi_release_protocol(struct scmi_handle *handle, u8 protocol_id)
> > +{
> > +       struct scmi_info *info = handle_to_scmi_info(handle);
> > +       struct scmi_protocol_instance *pi;
> > +
> > +       mutex_lock(&info->protocols_mtx);
> > +       /* Ensure protocols has been updated */
> > +       smp_rmb();
> > +       pi = info->protocols[protocol_id];
> > +       if (WARN_ON(!pi)) {
> > +               mutex_unlock(&info->protocols_mtx);
> > +               return;
> > +       }
> > +
> > +       if (refcount_dec_and_test(&pi->users)) {
> > +               void *gid = pi->gid;
> > +
> > +               if (pi->proto->deinit)
> > +                       pi->proto->deinit(handle);
> > +
> > +               info->protocols[protocol_id] = NULL;
> > +               /* Ensure deinitialized protocol is visible */
> > +               smp_wmb();
> > +
> > +               devres_release_group(handle->dev, gid);
> > +               dev_dbg(handle->dev, "De-Initialized protocol: 0x%X\n",
> > +                       protocol_id);
> > +       }
> > +       mutex_unlock(&info->protocols_mtx);
> > +}
> > +
> >  void scmi_setup_protocol_implemented(const struct scmi_handle *handle,
> >                                      u8 *prot_imp)
> >  {
> > @@ -785,6 +934,7 @@ static int scmi_probe(struct platform_device *pdev)
> >         info->dev = dev;
> >         info->desc = desc;
> >         INIT_LIST_HEAD(&info->node);
> > +       mutex_init(&info->protocols_mtx);
> >
> >         platform_set_drvdata(pdev, info);
> >         idr_init(&info->tx_idr);
> > @@ -805,10 +955,14 @@ static int scmi_probe(struct platform_device *pdev)
> >         if (scmi_notification_init(handle))
> >                 dev_err(dev, "SCMI Notifications NOT available.\n");
> >
> > -       ret = scmi_base_protocol_init(handle);
> > -       if (ret) {
> > -               dev_err(dev, "unable to communicate with SCMI(%d)\n", ret);
> > -               return ret;
> > +       /*
> > +        * Trigger SCMI Base protocol initialization.
> > +        * It's mandatory and won't be ever released/deinit until the
> > +        * SCMI stack is shutdown/unloaded as a whole.
> > +        */
> > +       if (scmi_acquire_protocol(handle, SCMI_PROTOCOL_BASE)) {
> > +               dev_err(dev, "unable to communicate with SCMI\n");
> > +               return -ENODEV;
> >         }
> >
> >         mutex_lock(&scmi_list_mutex);
> > @@ -941,6 +1095,8 @@ static int __init scmi_driver_init(void)
> >  {
> >         scmi_bus_init();
> >
> > +       scmi_base_register();
> > +
> >         scmi_clock_register();
> >         scmi_perf_register();
> >         scmi_power_register();
> > @@ -954,7 +1110,7 @@ subsys_initcall(scmi_driver_init);
> >
> >  static void __exit scmi_driver_exit(void)
> >  {
> > -       scmi_bus_exit();
> > +       scmi_base_unregister();
> >
> >         scmi_clock_unregister();
> >         scmi_perf_unregister();
> > @@ -963,6 +1119,8 @@ static void __exit scmi_driver_exit(void)
> >         scmi_sensors_unregister();
> >         scmi_system_unregister();
> >
> > +       scmi_bus_exit();
> > +
> >         platform_driver_unregister(&scmi_driver);
> >  }
> >  module_exit(scmi_driver_exit);
> > diff --git a/drivers/firmware/arm_scmi/notify.c b/drivers/firmware/arm_scmi/notify.c
> > index c24e427dce0d..eae58b2a92cc 100644
> > --- a/drivers/firmware/arm_scmi/notify.c
> > +++ b/drivers/firmware/arm_scmi/notify.c
> > @@ -91,10 +91,9 @@
> >  #include <linux/types.h>
> >  #include <linux/workqueue.h>
> >
> > +#include "common.h"
> >  #include "notify.h"
> >
> > -#define SCMI_MAX_PROTO         256
> > -
> >  #define PROTO_ID_MASK          GENMASK(31, 24)
> >  #define EVT_ID_MASK            GENMASK(23, 16)
> >  #define SRC_ID_MASK            GENMASK(15, 0)
> > diff --git a/drivers/firmware/arm_scmi/perf.c b/drivers/firmware/arm_scmi/perf.c
> > index 82fb3babff72..854460a051c2 100644
> > --- a/drivers/firmware/arm_scmi/perf.c
> > +++ b/drivers/firmware/arm_scmi/perf.c
> > @@ -2,7 +2,7 @@
> >  /*
> >   * System Control and Management Interface (SCMI) Performance Protocol
> >   *
> > - * Copyright (C) 2018 ARM Ltd.
> > + * Copyright (C) 2018-2020 ARM Ltd.
> >   */
> >
> >  #define pr_fmt(fmt) "SCMI Notifications PERF - " fmt
> > @@ -892,4 +892,10 @@ static int scmi_perf_protocol_init(struct scmi_handle *handle)
> >         return 0;
> >  }
> >
> > -DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(SCMI_PROTOCOL_PERF, perf)
> > +static struct scmi_protocol scmi_perf = {
> > +       .id = SCMI_PROTOCOL_PERF,
> > +       .init = &scmi_perf_protocol_init,
> > +       .ops = &perf_ops,
> > +};
> > +
> > +DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(perf, scmi_perf)
> > diff --git a/drivers/firmware/arm_scmi/power.c b/drivers/firmware/arm_scmi/power.c
> > index 1f37258e9bee..42c9c88da07c 100644
> > --- a/drivers/firmware/arm_scmi/power.c
> > +++ b/drivers/firmware/arm_scmi/power.c
> > @@ -2,7 +2,7 @@
> >  /*
> >   * System Control and Management Interface (SCMI) Power Protocol
> >   *
> > - * Copyright (C) 2018 ARM Ltd.
> > + * Copyright (C) 2018-2020 ARM Ltd.
> >   */
> >
> >  #define pr_fmt(fmt) "SCMI Notifications POWER - " fmt
> > @@ -301,4 +301,10 @@ static int scmi_power_protocol_init(struct scmi_handle *handle)
> >         return 0;
> >  }
> >
> > -DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(SCMI_PROTOCOL_POWER, power)
> > +static struct scmi_protocol scmi_power = {
> > +       .id = SCMI_PROTOCOL_POWER,
> > +       .init = &scmi_power_protocol_init,
> > +       .ops = &power_ops,
> > +};
> > +
> > +DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(power, scmi_power)
> > diff --git a/drivers/firmware/arm_scmi/reset.c b/drivers/firmware/arm_scmi/reset.c
> > index a981a22cfe89..2caf0bdb6fdc 100644
> > --- a/drivers/firmware/arm_scmi/reset.c
> > +++ b/drivers/firmware/arm_scmi/reset.c
> > @@ -2,7 +2,7 @@
> >  /*
> >   * System Control and Management Interface (SCMI) Reset Protocol
> >   *
> > - * Copyright (C) 2019 ARM Ltd.
> > + * Copyright (C) 2019-2020 ARM Ltd.
> >   */
> >
> >  #define pr_fmt(fmt) "SCMI Notifications RESET - " fmt
> > @@ -311,4 +311,10 @@ static int scmi_reset_protocol_init(struct scmi_handle *handle)
> >         return 0;
> >  }
> >
> > -DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(SCMI_PROTOCOL_RESET, reset)
> > +static struct scmi_protocol scmi_reset = {
> > +       .id = SCMI_PROTOCOL_RESET,
> > +       .init = &scmi_reset_protocol_init,
> > +       .ops = &reset_ops,
> > +};
> > +
> > +DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(reset, scmi_reset)
> > diff --git a/drivers/firmware/arm_scmi/sensors.c b/drivers/firmware/arm_scmi/sensors.c
> > index b4232d611033..dfe3076d2093 100644
> > --- a/drivers/firmware/arm_scmi/sensors.c
> > +++ b/drivers/firmware/arm_scmi/sensors.c
> > @@ -2,7 +2,7 @@
> >  /*
> >   * System Control and Management Interface (SCMI) Sensor Protocol
> >   *
> > - * Copyright (C) 2018 ARM Ltd.
> > + * Copyright (C) 2018-2020 ARM Ltd.
> >   */
> >
> >  #define pr_fmt(fmt) "SCMI Notifications SENSOR - " fmt
> > @@ -367,4 +367,10 @@ static int scmi_sensors_protocol_init(struct scmi_handle *handle)
> >         return 0;
> >  }
> >
> > -DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(SCMI_PROTOCOL_SENSOR, sensors)
> > +static struct scmi_protocol scmi_sensors = {
> > +       .id = SCMI_PROTOCOL_SENSOR,
> > +       .init = &scmi_sensors_protocol_init,
> > +       .ops = &sensor_ops,
> > +};
> > +
> > +DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(sensors, scmi_sensors)
> > diff --git a/drivers/firmware/arm_scmi/system.c b/drivers/firmware/arm_scmi/system.c
> > index 283e12d5f24b..bcea18bf54ab 100644
> > --- a/drivers/firmware/arm_scmi/system.c
> > +++ b/drivers/firmware/arm_scmi/system.c
> > @@ -128,4 +128,10 @@ static int scmi_system_protocol_init(struct scmi_handle *handle)
> >         return 0;
> >  }
> >
> > -DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(SCMI_PROTOCOL_SYSTEM, system)
> > +static struct scmi_protocol scmi_system = {
> > +       .id = SCMI_PROTOCOL_SYSTEM,
> > +       .init = &scmi_system_protocol_init,
> > +       .ops = NULL,
> > +};
> > +
> > +DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(system, scmi_system)
> > diff --git a/include/linux/scmi_protocol.h b/include/linux/scmi_protocol.h
> > index 9cd312a1ff92..ca23d682941e 100644
> > --- a/include/linux/scmi_protocol.h
> > +++ b/include/linux/scmi_protocol.h
> > @@ -376,9 +376,9 @@ static inline void scmi_driver_unregister(struct scmi_driver *driver) {}
> >  #define module_scmi_driver(__scmi_driver)      \
> >         module_driver(__scmi_driver, scmi_register, scmi_unregister)
> >
> > -typedef int (*scmi_prot_init_fn_t)(struct scmi_handle *);
> > -int scmi_protocol_register(int protocol_id, scmi_prot_init_fn_t fn);
> > -void scmi_protocol_unregister(int protocol_id);
> > +struct scmi_protocol;
> > +int scmi_protocol_register(struct scmi_protocol *proto);
> > +void scmi_protocol_unregister(const struct scmi_protocol *proto);
> >
> >  /* SCMI Notification API - Custom Event Reports */
> >  enum scmi_notification_events {
> > --
> > 2.17.1
> >