Date:   Wed, 14 Oct 2020 12:03:45 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Cristian Marussi <cristian.marussi@....com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc:     sudeep.holla@....com, lukasz.luba@....com,
        james.quinlan@...adcom.com, Jonathan.Cameron@...wei.com,
        etienne.carriere@...aro.org, thara.gopinath@...aro.org,
        vincent.guittot@...aro.org, souvik.chakravarty@....com
Subject: Re: [PATCH 01/11] firmware: arm_scmi: review protocol registration
 interface

On 10/14/20 8:05 AM, Cristian Marussi 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@....com>
> ---

[snip]

> +static struct scmi_protocol scmi_base = {
> +	.id = SCMI_PROTOCOL_BASE,
> +	.init = &scmi_base_protocol_init,
> +	.ops = NULL,
> +};

This could be const I believe.

> +
> +DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(base, scmi_base)
> diff --git a/drivers/firmware/arm_scmi/bus.c b/drivers/firmware/arm_scmi/bus.c
> index 1377ec76a45d..afa2e4818a2b 100644
> --- a/drivers/firmware/arm_scmi/bus.c
> +++ b/drivers/firmware/arm_scmi/bus.c
> @@ -16,7 +16,7 @@
>  #include "common.h"
>  
>  static DEFINE_IDA(scmi_bus_id);
> -static DEFINE_IDR(scmi_protocols);
> +static DEFINE_IDR(scmi_available_protocols);
>  static DEFINE_SPINLOCK(protocol_lock);
>  
>  static const struct scmi_device_id *
> @@ -51,13 +51,29 @@ static int scmi_dev_match(struct device *dev, struct device_driver *drv)
>  	return 0;
>  }
>  
> +const struct scmi_protocol *scmi_get_protocol(int protocol_id)
> +{
> +	const struct scmi_protocol *proto;
> +
> +	proto = idr_find(&scmi_available_protocols, protocol_id);
> +	if (!proto) {
> +		pr_warn("SCMI Protocol 0x%x not found!\n", protocol_id);
> +		return NULL;
> +	}
> +
> +	pr_debug("GOT SCMI Protocol 0x%x\n", protocol_id);
> +
> +	return proto;
> +}
> +
>  static int scmi_protocol_init(int protocol_id, struct scmi_handle *handle)
>  {
> -	scmi_prot_init_fn_t fn = idr_find(&scmi_protocols, protocol_id);
> +	const struct scmi_protocol *proto;
>  
> -	if (unlikely(!fn))
> +	proto = idr_find(&scmi_available_protocols, protocol_id);
> +	if (!proto)
>  		return -EINVAL;
> -	return fn(handle);
> +	return proto->init(handle);
>  }
>  
>  static int scmi_protocol_dummy_init(struct scmi_handle *handle)
> @@ -84,7 +100,7 @@ static int scmi_dev_probe(struct device *dev)
>  		return ret;
>  
>  	/* Skip protocol initialisation for additional devices */
> -	idr_replace(&scmi_protocols, &scmi_protocol_dummy_init,
> +	idr_replace(&scmi_available_protocols, &scmi_protocol_dummy_init,
>  		    scmi_dev->protocol_id);
>  
>  	return scmi_drv->probe(scmi_dev);
> @@ -194,26 +210,45 @@ void scmi_set_handle(struct scmi_device *scmi_dev)
>  	scmi_dev->handle = scmi_handle_get(&scmi_dev->dev);
>  }
>  
> -int scmi_protocol_register(int protocol_id, scmi_prot_init_fn_t fn)
> +int scmi_protocol_register(struct scmi_protocol *proto)

And this could probably take a const struct scmi_protocol here too as
you do not appear to be modifying proto, idr_alloc() may complain.

[snip]

>  
> -DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(SCMI_PROTOCOL_CLOCK, clock)
> +static struct scmi_protocol scmi_clock = {

static const here too and throughout your submission.

[snip]

> +	struct scmi_protocol_instance *protocols[SCMI_MAX_PROTO];

Humm that would be 2048 bytes on a 64-bit platform and 1024 bytes on a
32-bit platform, this is not so bad, but it is a bit wasteful given that
6-7 standard protocols are typically found, and most often no
proprietary protocols are registered. Not necessarily to be addressed
right now.

> +	/* Ensure mutual exclusive access to protocols instance array */
> +	struct mutex protocols_mtx;
>  	u8 *protocols_imp;
>  	struct list_head node;
>  	int users;
> @@ -519,6 +542,132 @@ int scmi_version_get(const struct scmi_handle *handle, u8 protocol,
>  	return ret;
>  }
>  
> +/**
> + * 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();
> +	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;

You could return -ENODEV here and propagate that error code for
scmi_probe() to use as -is.

> +			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);
> +	}

You may be able to re-arrange the indentation and do:

	if (pi) {
		refcount_inc(&pi->users);
		mutex_unlock(&info->protocols_mtx);
		return pi;
	}

to reduce the indentation level, and this would also have the fast path
tested first.

> +	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;

Maybe define an "out" label just to avoid the repetition?

> +	}
> +
> +	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;

and you could do:

ret = scmi_acquire_protocol(.., ...);
if (ret) {
	dev_err(dev, "unable to communicate with SCMI\n");
	return ret;
}

Everything else looked good to me, thanks!
-- 
Florian

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