Message-ID: <af23ce35-4c58-678b-eb20-c4072c358db3@opensynergy.com>
Date:   Fri, 4 Jun 2021 11:19:02 +0200
From:   Peter Hilber <peter.hilber@...nsynergy.com>
To:     Cristian Marussi <cristian.marussi@....com>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>,
        <virtualization@...ts.linux-foundation.org>,
        <virtio-dev@...ts.oasis-open.org>,
        Igor Skalkin <igor.skalkin@...nsynergy.com>,
        Rob Herring <robh+dt@...nel.org>,
        <linux-kernel@...r.kernel.org>, <sudeep.holla@....com>,
        <souvik.chakravarty@....com>, <alex.bennee@...aro.org>,
        <jean-philippe@...aro.org>, <mikhail.golubev@...nsynergy.com>,
        <anton.yakovlev@...nsynergy.com>,
        Vasyl Vavrychuk <Vasyl.Vavrychuk@...nsynergy.com>,
        Andriy Tryshnivskyy <Andriy.Tryshnivskyy@...nsynergy.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: [RFC PATCH v3 11/12] firmware: arm_scmi: Add virtio transport

On 26.05.21 16:40, Cristian Marussi wrote:
> Hi Peter,
> 
> as anticipated I'm adding some new SCMI core mechanisms that should help
> simplyfying virtio-scmi series.
> 
> Such core work is still in progress (and to be properly reviewed) and it
> is at:
> 
> https://lore.kernel.org/linux-arm-kernel/20210524231503.34924-1-cristian.marussi@arm.com/
> 
> but in the meantime I have an initial but working (for me at least :D)
> rework of your V3 virtio-scmi series; rework is still in progress and to be
> cleaned up (nor I have addressed probing sequence or polling mode), and I am
> anyway holding it for now since Rob asked about DT txt-to-yaml conversion
> too, BUT if you can or want to have a look in the meantime, you can find the
> whole V4 transitional series rebased on top of my core changes with some
> changes on top at:
> 
> https://gitlab.arm.com/linux-arm/linux-cm/-/commits/scmi_virtio_trans_V4_rework/
> 
> where:
> 
>  - I dropped V3 patches 7,8,12
>  - the virtio changes I applied to make use of my core changes are all
>    embedded in the last patch (just for now):
>    
>  	[RFC] firmware: arm_scmi: make virtio-scmi use delegated xfers
> 
> Definitely not the final version, so you may want to just wait for a
> real V4, but just to give an idea of the direction I'm trying to follow
> if you want.
> 
> Thanks,
> Cristian
> 

Hi Cristian,

I had a look at the concepts in the linked branch. The following race
condition seems to not be addressed ATM:

- concurrent not delayed and delayed response (or inverted order)

The virtio device will send the not delayed and delayed response through
different virtqueues. Sending in a particular order will in my
understanding not entail that the receiver is able to restore this
order. I think the virtio transport cannot handle this race condition in
general without interpreting message headers (which it shouldn't).

Also, it might be documented that after a response timeout, do_xfer
should not be called on the xfer any more (since a belated response to
the timed out message might corrupt the new message).

Best regards,

Peter

> On Tue, May 11, 2021 at 02:20:39AM +0200, Peter Hilber wrote:
>> From: Igor Skalkin <igor.skalkin@...nsynergy.com>
>>
>> This transport enables accessing an SCMI platform as a virtio device.
>>
>> Implement an SCMI virtio driver according to the virtio SCMI device spec
>> [1]. Virtio device id 32 has been reserved for the SCMI device [2].
>>
>> The virtio transport has one Tx channel (virtio cmdq, A2P channel) and
>> at most one Rx channel (virtio eventq, P2A channel).
>>
>> The following feature bit defined in [1] is not implemented:
>> VIRTIO_SCMI_F_SHARED_MEMORY.
>>
>> After the preparatory patches, this implements the virtio transport as
>> paraphrased:
>>
>> Only support a single arm-scmi device (which is consistent with the SCMI
>> spec). scmi-virtio init is called from arm-scmi module init. During the
>> arm-scmi probing, link to the first probed scmi-virtio device. Defer
>> arm-scmi probing if no scmi-virtio device is bound yet.
>>
>> For simplicity, restrict the number of messages which can be pending
>> simultaneously according to the virtqueue capacity. (The virtqueue sizes
>> are negotiated with the virtio device.)
>>
>> As soon as Rx channel message buffers are allocated or have been read
>> out by the arm-scmi driver, feed them to the virtio device.
>>
>> Since some virtio devices may not have the short response time exhibited
>> by SCMI platforms using other transports, set a generous response
>> timeout.
>>
>> Limitations:
>>
>> - Polling is not supported.
>>
>> - The timeout for delayed responses has not been adjusted.
>>
>> [1] https://github.com/oasis-tcs/virtio-spec/blob/master/virtio-scmi.tex
>> [2] https://www.oasis-open.org/committees/ballot.php?id=3496
>>
>> Signed-off-by: Igor Skalkin <igor.skalkin@...nsynergy.com>
>> [ Peter: Adapted patch for submission to upstream. ]
>> Co-developed-by: Peter Hilber <peter.hilber@...nsynergy.com>
>> Signed-off-by: Peter Hilber <peter.hilber@...nsynergy.com>
>> ---
>>  MAINTAINERS                        |   1 +
>>  drivers/firmware/Kconfig           |  12 +
>>  drivers/firmware/arm_scmi/Makefile |   1 +
>>  drivers/firmware/arm_scmi/common.h |   3 +
>>  drivers/firmware/arm_scmi/driver.c |   3 +
>>  drivers/firmware/arm_scmi/virtio.c | 523 +++++++++++++++++++++++++++++
>>  include/uapi/linux/virtio_ids.h    |   1 +
>>  include/uapi/linux/virtio_scmi.h   |  25 ++
>>  8 files changed, 569 insertions(+)
>>  create mode 100644 drivers/firmware/arm_scmi/virtio.c
>>  create mode 100644 include/uapi/linux/virtio_scmi.h
>>
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index bd7aff0c120f..449c336872f3 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -17705,6 +17705,7 @@ F:	drivers/regulator/scmi-regulator.c
>>  F:	drivers/reset/reset-scmi.c
>>  F:	include/linux/sc[mp]i_protocol.h
>>  F:	include/trace/events/scmi.h
>> +F:	include/uapi/linux/virtio_scmi.h
>>  
>>  SYSTEM RESET/SHUTDOWN DRIVERS
>>  M:	Sebastian Reichel <sre@...nel.org>
>> diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
>> index e8377b12e4d0..7e9eafdd9b63 100644
>> --- a/drivers/firmware/Kconfig
>> +++ b/drivers/firmware/Kconfig
>> @@ -39,6 +39,18 @@ config ARM_SCMI_HAVE_MSG
>>  	  This declares whether a message passing based transport for SCMI is
>>  	  available.
>>  
>> +# This config option includes the dependencies of ARM_SCMI_PROTOCOL so that
>> +# this config doesn't show up when SCMI wouldn't be available.
>> +config VIRTIO_SCMI
>> +	bool "Virtio transport for SCMI"
>> +	select ARM_SCMI_HAVE_MSG
>> +	depends on VIRTIO && (ARM || ARM64 || COMPILE_TEST)
>> +	help
>> +	  This enables the virtio based transport for SCMI.
>> +
>> +	  If you want to use the ARM SCMI protocol between the virtio guest and
>> +	  a host providing a virtio SCMI device, answer Y.
>> +
>>  config ARM_SCMI_POWER_DOMAIN
>>  	tristate "SCMI power domain driver"
>>  	depends on ARM_SCMI_PROTOCOL || (COMPILE_TEST && OF)
>> diff --git a/drivers/firmware/arm_scmi/Makefile b/drivers/firmware/arm_scmi/Makefile
>> index f6b4acb8abdb..db1787606fb2 100644
>> --- a/drivers/firmware/arm_scmi/Makefile
>> +++ b/drivers/firmware/arm_scmi/Makefile
>> @@ -5,6 +5,7 @@ scmi-transport-$(CONFIG_ARM_SCMI_HAVE_SHMEM) = shmem.o
>>  scmi-transport-$(CONFIG_MAILBOX) += mailbox.o
>>  scmi-transport-$(CONFIG_HAVE_ARM_SMCCC_DISCOVERY) += smc.o
>>  scmi-transport-$(CONFIG_ARM_SCMI_HAVE_MSG) += msg.o
>> +scmi-transport-$(CONFIG_VIRTIO_SCMI) += virtio.o
>>  scmi-protocols-y = base.o clock.o perf.o power.o reset.o sensors.o system.o voltage.o
>>  scmi-module-objs := $(scmi-bus-y) $(scmi-driver-y) $(scmi-protocols-y) \
>>  		    $(scmi-transport-y)
>> diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
>> index 4cb6571c7aaf..bada06cfd33d 100644
>> --- a/drivers/firmware/arm_scmi/common.h
>> +++ b/drivers/firmware/arm_scmi/common.h
>> @@ -349,6 +349,9 @@ extern const struct scmi_desc scmi_mailbox_desc;
>>  #ifdef CONFIG_HAVE_ARM_SMCCC
>>  extern const struct scmi_desc scmi_smc_desc;
>>  #endif
>> +#ifdef CONFIG_VIRTIO_SCMI
>> +extern const struct scmi_desc scmi_virtio_desc;
>> +#endif
>>  
>>  int scmi_set_transport_info(struct device *dev, void *transport_info);
>>  void *scmi_get_transport_info(struct device *dev);
>> diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
>> index e04e7c8e6928..a31187385470 100644
>> --- a/drivers/firmware/arm_scmi/driver.c
>> +++ b/drivers/firmware/arm_scmi/driver.c
>> @@ -1637,6 +1637,9 @@ static const struct of_device_id scmi_of_match[] = {
>>  #endif
>>  #ifdef CONFIG_HAVE_ARM_SMCCC_DISCOVERY
>>  	{ .compatible = "arm,scmi-smc", .data = &scmi_smc_desc},
>> +#endif
>> +#ifdef CONFIG_VIRTIO_SCMI
>> +	{ .compatible = "arm,scmi-virtio", .data = &scmi_virtio_desc},
>>  #endif
>>  	{ /* Sentinel */ },
>>  };
>> diff --git a/drivers/firmware/arm_scmi/virtio.c b/drivers/firmware/arm_scmi/virtio.c
>> new file mode 100644
>> index 000000000000..20972adf6dc7
>> --- /dev/null
>> +++ b/drivers/firmware/arm_scmi/virtio.c
>> @@ -0,0 +1,523 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Virtio Transport driver for Arm System Control and Management Interface
>> + * (SCMI).
>> + *
>> + * Copyright (C) 2020 OpenSynergy.
>> + */
>> +
>> +/**
>> + * DOC: Theory of Operation
>> + *
>> + * The scmi-virtio transport implements a driver for the virtio SCMI device.
>> + *
>> + * There is one Tx channel (virtio cmdq, A2P channel) and at most one Rx
>> + * channel (virtio eventq, P2A channel). Each channel is implemented through a
>> + * virtqueue. Access to each virtqueue is protected by spinlocks.
>> + */
>> +
>> +#include <linux/errno.h>
>> +#include <linux/of.h>
>> +#include <linux/of_platform.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/module.h>
>> +#include <linux/slab.h>
>> +#include <linux/virtio.h>
>> +#include <linux/virtio_config.h>
>> +#include <uapi/linux/virtio_ids.h>
>> +#include <uapi/linux/virtio_scmi.h>
>> +
>> +#include "common.h"
>> +
>> +#define VIRTIO_SCMI_MAX_MSG_SIZE 128 /* Value may be increased. */
>> +#define VIRTIO_SCMI_MAX_PDU_SIZE \
>> +	(VIRTIO_SCMI_MAX_MSG_SIZE + SCMI_MSG_MAX_PROT_OVERHEAD)
>> +#define DESCRIPTORS_PER_TX_MSG 2
>> +
>> +/**
>> + * struct scmi_vio_channel - Transport channel information
>> + *
>> + * @lock: Protects access to all members except ready.
>> + * @ready_lock: Protects access to ready. If required, it must be taken before
>> + *              lock.
>> + * @vqueue: Associated virtqueue
>> + * @cinfo: SCMI Tx or Rx channel
>> + * @free_list: List of unused scmi_vio_msg, maintained for Tx channels only
>> + * @is_rx: Whether channel is an Rx channel
>> + * @ready: Whether transport user is ready to hear about channel
>> + */
>> +struct scmi_vio_channel {
>> +	spinlock_t lock;
>> +	spinlock_t ready_lock;
>> +	struct virtqueue *vqueue;
>> +	struct scmi_chan_info *cinfo;
>> +	struct list_head free_list;
>> +	u8 is_rx;
>> +	u8 ready;
>> +};
>> +
>> +/**
>> + * struct scmi_vio_msg - Transport PDU information
>> + *
>> + * @request: SDU used for commands
>> + * @input: SDU used for (delayed) responses and notifications
>> + * @list: List which scmi_vio_msg may be part of
>> + * @rx_len: Input SDU size in bytes, once input has been received
>> + */
>> +struct scmi_vio_msg {
>> +	struct scmi_msg_payld *request;
>> +	struct scmi_msg_payld *input;
>> +	struct list_head list;
>> +	unsigned int rx_len;
>> +};
>> +
>> +static bool scmi_vio_have_vq_rx(struct virtio_device *vdev)
>> +{
>> +	return virtio_has_feature(vdev, VIRTIO_SCMI_F_P2A_CHANNELS);
>> +}
>> +
>> +static int scmi_vio_feed_vq_rx(struct scmi_vio_channel *vioch,
>> +			       struct scmi_vio_msg *msg)
>> +{
>> +	struct scatterlist sg_in;
>> +	int rc;
>> +	unsigned long flags;
>> +
>> +	sg_init_one(&sg_in, msg->input, VIRTIO_SCMI_MAX_PDU_SIZE);
>> +
>> +	spin_lock_irqsave(&vioch->lock, flags);
>> +
>> +	rc = virtqueue_add_inbuf(vioch->vqueue, &sg_in, 1, msg, GFP_ATOMIC);
>> +	if (rc)
>> +		dev_err_once(vioch->cinfo->dev,
>> +			     "%s() failed to add to virtqueue (%d)\n", __func__,
>> +			     rc);
>> +	else
>> +		virtqueue_kick(vioch->vqueue);
>> +
>> +	spin_unlock_irqrestore(&vioch->lock, flags);
>> +
>> +	return rc;
>> +}
>> +
>> +static void scmi_vio_complete_cb(struct virtqueue *vqueue)
>> +{
>> +	unsigned long ready_flags;
>> +	unsigned long flags;
>> +	unsigned int length;
>> +	struct scmi_vio_channel *vioch;
>> +	struct scmi_vio_msg *msg;
>> +	bool cb_enabled = true;
>> +
>> +	if (WARN_ON_ONCE(!vqueue->vdev->priv))
>> +		return;
>> +	vioch = &((struct scmi_vio_channel *)vqueue->vdev->priv)[vqueue->index];
>> +
>> +	for (;;) {
>> +		spin_lock_irqsave(&vioch->ready_lock, ready_flags);
>> +
>> +		if (!vioch->ready) {
>> +			if (!cb_enabled)
>> +				(void)virtqueue_enable_cb(vqueue);
>> +			goto unlock_ready_out;
>> +		}
>> +
>> +		spin_lock_irqsave(&vioch->lock, flags);
>> +		if (cb_enabled) {
>> +			virtqueue_disable_cb(vqueue);
>> +			cb_enabled = false;
>> +		}
>> +		msg = virtqueue_get_buf(vqueue, &length);
>> +		if (!msg) {
>> +			if (virtqueue_enable_cb(vqueue))
>> +				goto unlock_out;
>> +			else
>> +				cb_enabled = true;
>> +		}
>> +		spin_unlock_irqrestore(&vioch->lock, flags);
>> +
>> +		if (msg) {
>> +			msg->rx_len = length;
>> +
>> +			/*
>> +			 * Hold the ready_lock during the callback to avoid
>> +			 * races when the arm-scmi driver is unbinding while
>> +			 * the virtio device is not quiesced yet.
>> +			 */
>> +			scmi_rx_callback(vioch->cinfo,
>> +					 msg_read_header(msg->input), msg);
>> +		}
>> +		spin_unlock_irqrestore(&vioch->ready_lock, ready_flags);
>> +	}
>> +
>> +unlock_out:
>> +	spin_unlock_irqrestore(&vioch->lock, flags);
>> +unlock_ready_out:
>> +	spin_unlock_irqrestore(&vioch->ready_lock, ready_flags);
>> +}
>> +
>> +static const char *const scmi_vio_vqueue_names[] = { "tx", "rx" };
>> +
>> +static vq_callback_t *scmi_vio_complete_callbacks[] = {
>> +	scmi_vio_complete_cb,
>> +	scmi_vio_complete_cb
>> +};
>> +
>> +static unsigned int virtio_get_max_msg(bool tx,
>> +				       struct scmi_chan_info *base_cinfo)
>> +{
>> +	struct scmi_vio_channel *vioch = base_cinfo->transport_info;
>> +	unsigned int ret;
>> +
>> +	ret = virtqueue_get_vring_size(vioch->vqueue);
>> +
>> +	/* Tx messages need multiple descriptors. */
>> +	if (tx)
>> +		ret /= DESCRIPTORS_PER_TX_MSG;
>> +
>> +	if (ret > MSG_TOKEN_MAX) {
>> +		dev_info_once(
>> +			base_cinfo->dev,
>> +			"Only %ld messages can be pending simultaneously, while the %s virtqueue could hold %d\n",
>> +			MSG_TOKEN_MAX, tx ? "tx" : "rx", ret);
>> +		ret = MSG_TOKEN_MAX;
>> +	}
>> +
>> +	return ret;
>> +}
>> +
>> +static int scmi_vio_match_any_dev(struct device *dev, const void *data)
>> +{
>> +	return 1;
>> +}
>> +
>> +static struct virtio_driver virtio_scmi_driver; /* Forward declaration */
>> +
>> +static int virtio_link_supplier(struct device *dev)
>> +{
>> +	struct device *vdev = driver_find_device(
>> +		&virtio_scmi_driver.driver, NULL, NULL, scmi_vio_match_any_dev);
>> +
>> +	if (!vdev) {
>> +		dev_notice_once(
>> +			dev,
>> +			"Deferring probe after not finding a bound scmi-virtio device\n");
>> +		return -EPROBE_DEFER;
>> +	}
>> +
>> +	/* Add device link for remove order and sysfs link. */
>> +	if (!device_link_add(dev, vdev, DL_FLAG_AUTOREMOVE_CONSUMER)) {
>> +		put_device(vdev);
>> +		dev_err(dev, "Adding link to supplier virtio device failed\n");
>> +		return -ECANCELED;
>> +	}
>> +
>> +	put_device(vdev);
>> +	return scmi_set_transport_info(dev, dev_to_virtio(vdev));
>> +}
>> +
>> +static bool virtio_chan_available(struct device *dev, int idx)
>> +{
>> +	struct virtio_device *vdev;
>> +
>> +	/* scmi-virtio doesn't support per-protocol channels */
>> +	if (is_scmi_protocol_device(dev))
>> +		return false;
>> +
>> +	vdev = scmi_get_transport_info(dev);
>> +	if (!vdev)
>> +		return false;
>> +
>> +	switch (idx) {
>> +	case VIRTIO_SCMI_VQ_TX:
>> +		return true;
>> +	case VIRTIO_SCMI_VQ_RX:
>> +		return scmi_vio_have_vq_rx(vdev);
>> +	default:
>> +		return false;
>> +	}
>> +}
>> +
>> +static int virtio_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
>> +			     bool tx)
>> +{
>> +	unsigned long flags;
>> +	struct virtio_device *vdev;
>> +	struct scmi_vio_channel *vioch;
>> +	int index = tx ? VIRTIO_SCMI_VQ_TX : VIRTIO_SCMI_VQ_RX;
>> +	int max_msg;
>> +	int i;
>> +
>> +	if (!virtio_chan_available(dev, index))
>> +		return -ENODEV;
>> +
>> +	vdev = scmi_get_transport_info(dev);
>> +	vioch = &((struct scmi_vio_channel *)vdev->priv)[index];
>> +
>> +	spin_lock_irqsave(&vioch->lock, flags);
>> +	cinfo->transport_info = vioch;
>> +	vioch->cinfo = cinfo;
>> +	spin_unlock_irqrestore(&vioch->lock, flags);
>> +
>> +	max_msg = virtio_get_max_msg(tx, cinfo);
>> +
>> +	for (i = 0; i < max_msg; i++) {
>> +		struct scmi_vio_msg *msg;
>> +
>> +		msg = devm_kzalloc(cinfo->dev, sizeof(*msg), GFP_KERNEL);
>> +		if (!msg)
>> +			return -ENOMEM;
>> +
>> +		if (tx) {
>> +			msg->request = devm_kzalloc(cinfo->dev,
>> +						    VIRTIO_SCMI_MAX_PDU_SIZE,
>> +						    GFP_KERNEL);
>> +			if (!msg->request)
>> +				return -ENOMEM;
>> +		}
>> +
>> +		msg->input = devm_kzalloc(cinfo->dev, VIRTIO_SCMI_MAX_PDU_SIZE,
>> +					  GFP_KERNEL);
>> +		if (!msg->input)
>> +			return -ENOMEM;
>> +
>> +		if (tx) {
>> +			spin_lock_irqsave(&vioch->lock, flags);
>> +			list_add_tail(&msg->list, &vioch->free_list);
>> +			spin_unlock_irqrestore(&vioch->lock, flags);
>> +		} else {
>> +			scmi_vio_feed_vq_rx(vioch, msg);
>> +		}
>> +	}
>> +
>> +	spin_lock_irqsave(&vioch->ready_lock, flags);
>> +	vioch->ready = true;
>> +	spin_unlock_irqrestore(&vioch->ready_lock, flags);
>> +
>> +	return 0;
>> +}
>> +
>> +static int virtio_chan_free(int id, void *p, void *data)
>> +{
>> +	unsigned long flags;
>> +	struct scmi_chan_info *cinfo = p;
>> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
>> +
>> +	spin_lock_irqsave(&vioch->ready_lock, flags);
>> +	vioch->ready = false;
>> +	spin_unlock_irqrestore(&vioch->ready_lock, flags);
>> +
>> +	scmi_free_channel(cinfo, data, id);
>> +	return 0;
>> +}
>> +
>> +static int virtio_send_message(struct scmi_chan_info *cinfo,
>> +			       struct scmi_xfer *xfer)
>> +{
>> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
>> +	struct scatterlist sg_out;
>> +	struct scatterlist sg_in;
>> +	struct scatterlist *sgs[DESCRIPTORS_PER_TX_MSG] = { &sg_out, &sg_in };
>> +	unsigned long flags;
>> +	int rc;
>> +	struct scmi_vio_msg *msg;
>> +
>> +	/*
>> +	 * TODO: For now, we don't support polling. But it should not be
>> +	 * difficult to add support.
>> +	 */
>> +	if (xfer->hdr.poll_completion)
>> +		return -EINVAL;
>> +
>> +	spin_lock_irqsave(&vioch->lock, flags);
>> +
>> +	if (list_empty(&vioch->free_list)) {
>> +		spin_unlock_irqrestore(&vioch->lock, flags);
>> +		return -EBUSY;
>> +	}
>> +
>> +	msg = list_first_entry(&vioch->free_list, typeof(*msg), list);
>> +	list_del(&msg->list);
>> +
>> +	msg_tx_prepare(msg->request, xfer);
>> +
>> +	sg_init_one(&sg_out, msg->request, msg_command_size(xfer));
>> +	sg_init_one(&sg_in, msg->input, msg_response_size(xfer));
>> +
>> +	rc = virtqueue_add_sgs(vioch->vqueue, sgs, 1, 1, msg, GFP_ATOMIC);
>> +	if (rc) {
>> +		list_add(&msg->list, &vioch->free_list);
>> +		dev_err_once(vioch->cinfo->dev,
>> +			     "%s() failed to add to virtqueue (%d)\n", __func__,
>> +			     rc);
>> +	} else {
>> +		virtqueue_kick(vioch->vqueue);
>> +	}
>> +
>> +	spin_unlock_irqrestore(&vioch->lock, flags);
>> +
>> +	return rc;
>> +}
>> +
>> +static void virtio_fetch_response(struct scmi_chan_info *cinfo,
>> +				  struct scmi_xfer *xfer, void *msg_handle)
>> +{
>> +	struct scmi_vio_msg *msg = msg_handle;
>> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
>> +
>> +	if (!msg) {
>> +		dev_dbg_once(&vioch->vqueue->vdev->dev,
>> +			     "Ignoring %s() call with NULL msg_handle\n",
>> +			     __func__);
>> +		return;
>> +	}
>> +
>> +	msg_fetch_response(msg->input, msg->rx_len, xfer);
>> +}
>> +
>> +static void virtio_fetch_notification(struct scmi_chan_info *cinfo,
>> +				      size_t max_len, struct scmi_xfer *xfer,
>> +				      void *msg_handle)
>> +{
>> +	struct scmi_vio_msg *msg = msg_handle;
>> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
>> +
>> +	if (!msg) {
>> +		dev_dbg_once(&vioch->vqueue->vdev->dev,
>> +			     "Ignoring %s() call with NULL msg_handle\n",
>> +			     __func__);
>> +		return;
>> +	}
>> +
>> +	msg_fetch_notification(msg->input, msg->rx_len, max_len, xfer);
>> +}
>> +
>> +static void dummy_clear_channel(struct scmi_chan_info *cinfo)
>> +{
>> +}
>> +
>> +static bool dummy_poll_done(struct scmi_chan_info *cinfo,
>> +			    struct scmi_xfer *xfer)
>> +{
>> +	return false;
>> +}
>> +
>> +static void virtio_drop_message(struct scmi_chan_info *cinfo, void *msg_handle)
>> +{
>> +	unsigned long flags;
>> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
>> +	struct scmi_vio_msg *msg = msg_handle;
>> +
>> +	if (!msg) {
>> +		dev_dbg_once(&vioch->vqueue->vdev->dev,
>> +			     "Ignoring %s() call with NULL msg_handle\n",
>> +			     __func__);
>> +		return;
>> +	}
>> +
>> +	if (vioch->is_rx) {
>> +		scmi_vio_feed_vq_rx(vioch, msg);
>> +	} else {
>> +		spin_lock_irqsave(&vioch->lock, flags);
>> +		list_add(&msg->list, &vioch->free_list);
>> +		spin_unlock_irqrestore(&vioch->lock, flags);
>> +	}
>> +}
>> +
>> +static const struct scmi_transport_ops scmi_virtio_ops = {
>> +	.link_supplier = virtio_link_supplier,
>> +	.chan_available = virtio_chan_available,
>> +	.chan_setup = virtio_chan_setup,
>> +	.chan_free = virtio_chan_free,
>> +	.get_max_msg = virtio_get_max_msg,
>> +	.send_message = virtio_send_message,
>> +	.fetch_response = virtio_fetch_response,
>> +	.fetch_notification = virtio_fetch_notification,
>> +	.clear_channel = dummy_clear_channel,
>> +	.poll_done = dummy_poll_done,
>> +	.drop_message = virtio_drop_message,
>> +};
>> +
>> +static int scmi_vio_probe(struct virtio_device *vdev)
>> +{
>> +	struct device *dev = &vdev->dev;
>> +	struct scmi_vio_channel *channels;
>> +	bool have_vq_rx;
>> +	int vq_cnt;
>> +	int i;
>> +	int ret;
>> +	struct virtqueue *vqs[VIRTIO_SCMI_VQ_MAX_CNT];
>> +
>> +	have_vq_rx = scmi_vio_have_vq_rx(vdev);
>> +	vq_cnt = have_vq_rx ? VIRTIO_SCMI_VQ_MAX_CNT : 1;
>> +
>> +	channels = devm_kcalloc(dev, vq_cnt, sizeof(*channels), GFP_KERNEL);
>> +	if (!channels)
>> +		return -ENOMEM;
>> +
>> +	if (have_vq_rx)
>> +		channels[VIRTIO_SCMI_VQ_RX].is_rx = true;
>> +
>> +	ret = virtio_find_vqs(vdev, vq_cnt, vqs, scmi_vio_complete_callbacks,
>> +			      scmi_vio_vqueue_names, NULL);
>> +	if (ret) {
>> +		dev_err(dev, "Failed to get %d virtqueue(s)\n", vq_cnt);
>> +		return ret;
>> +	}
>> +	dev_info(dev, "Found %d virtqueue(s)\n", vq_cnt);
>> +
>> +	for (i = 0; i < vq_cnt; i++) {
>> +		spin_lock_init(&channels[i].lock);
>> +		spin_lock_init(&channels[i].ready_lock);
>> +		INIT_LIST_HEAD(&channels[i].free_list);
>> +		channels[i].vqueue = vqs[i];
>> +	}
>> +
>> +	vdev->priv = channels;
>> +
>> +	return 0;
>> +}
>> +
>> +static void scmi_vio_remove(struct virtio_device *vdev)
>> +{
>> +	vdev->config->reset(vdev);
>> +	vdev->config->del_vqs(vdev);
>> +}
>> +
>> +static unsigned int features[] = {
>> +	VIRTIO_SCMI_F_P2A_CHANNELS,
>> +};
>> +
>> +static const struct virtio_device_id id_table[] = {
>> +	{ VIRTIO_ID_SCMI, VIRTIO_DEV_ANY_ID },
>> +	{ 0 }
>> +};
>> +
>> +static struct virtio_driver virtio_scmi_driver = {
>> +	.driver.name = "scmi-virtio",
>> +	.driver.owner = THIS_MODULE,
>> +	.feature_table = features,
>> +	.feature_table_size = ARRAY_SIZE(features),
>> +	.id_table = id_table,
>> +	.probe = scmi_vio_probe,
>> +	.remove = scmi_vio_remove,
>> +};
>> +
>> +static int __init virtio_scmi_init(void)
>> +{
>> +	return register_virtio_driver(&virtio_scmi_driver);
>> +}
>> +
>> +static void __exit virtio_scmi_exit(void)
>> +{
>> +	unregister_virtio_driver(&virtio_scmi_driver);
>> +}
>> +
>> +const struct scmi_desc scmi_virtio_desc = {
>> +	.init = virtio_scmi_init,
>> +	.exit = virtio_scmi_exit,
>> +	.ops = &scmi_virtio_ops,
>> +	.max_rx_timeout_ms = 60000, /* for non-realtime virtio devices */
>> +	.max_msg = 0, /* overridden by virtio_get_max_msg() */
>> +	.max_msg_size = VIRTIO_SCMI_MAX_MSG_SIZE,
>> +};
>> diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
>> index f0c35ce8628c..c146fe30e589 100644
>> --- a/include/uapi/linux/virtio_ids.h
>> +++ b/include/uapi/linux/virtio_ids.h
>> @@ -56,5 +56,6 @@
>>  #define VIRTIO_ID_PMEM			27 /* virtio pmem */
>>  #define VIRTIO_ID_BT			28 /* virtio bluetooth */
>>  #define VIRTIO_ID_MAC80211_HWSIM	29 /* virtio mac80211-hwsim */
>> +#define VIRTIO_ID_SCMI			32 /* virtio SCMI */
>>  
>>  #endif /* _LINUX_VIRTIO_IDS_H */
>> diff --git a/include/uapi/linux/virtio_scmi.h b/include/uapi/linux/virtio_scmi.h
>> new file mode 100644
>> index 000000000000..732b01504c35
>> --- /dev/null
>> +++ b/include/uapi/linux/virtio_scmi.h
>> @@ -0,0 +1,25 @@
>> +/* SPDX-License-Identifier: ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) */
>> +/*
>> + * Copyright (C) 2020 OpenSynergy GmbH
>> + */
>> +
>> +#ifndef _UAPI_LINUX_VIRTIO_SCMI_H
>> +#define _UAPI_LINUX_VIRTIO_SCMI_H
>> +
>> +#include <linux/virtio_types.h>
>> +
>> +/* Feature bits */
>> +
>> +/* Device implements some SCMI notifications, or delayed responses. */
>> +#define VIRTIO_SCMI_F_P2A_CHANNELS 0
>> +
>> +/* Device implements any SCMI statistics shared memory region */
>> +#define VIRTIO_SCMI_F_SHARED_MEMORY 1
>> +
>> +/* Virtqueues */
>> +
>> +#define VIRTIO_SCMI_VQ_TX 0 /* cmdq */
>> +#define VIRTIO_SCMI_VQ_RX 1 /* eventq */
>> +#define VIRTIO_SCMI_VQ_MAX_CNT 2
>> +
>> +#endif /* _UAPI_LINUX_VIRTIO_SCMI_H */
>> -- 
>> 2.25.1
>>
>>
> 

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