Commit 0bfdca8a authored by Cristian Marussi's avatar Cristian Marussi Committed by Sudeep Holla
Browse files

firmware: arm_scmi: Add atomic mode support to smc transport 

Add a Kernel configuration option to enable SCMI SMC transport atomic
mode operation for selected SCMI transactions and leave it as default
disabled.

Substitute mutex usages with busy-waiting and declare smc transport as
.atomic_enabled if such Kernel configuration option is enabled.

Link: https://lore.kernel.org/r/20211220195646.44498-8-cristian.marussi@arm.com


Signed-off-by: default avatarCristian Marussi <cristian.marussi@arm.com>
Signed-off-by: default avatarSudeep Holla <sudeep.holla@arm.com>
parent 69255e74

drivers/firmware/arm_scmi/Kconfig

+14 −0
Original line number Diff line number Diff line
@@ -78,6 +78,20 @@ config ARM_SCMI_TRANSPORT_SMC 
	  If you want the ARM SCMI PROTOCOL stack to include support for a

	  transport based on SMC, answer Y.



config ARM_SCMI_TRANSPORT_SMC_ATOMIC_ENABLE

	bool "Enable atomic mode support for SCMI SMC transport"

	depends on ARM_SCMI_TRANSPORT_SMC

	help

	  Enable support of atomic operation for SCMI SMC based transport.



	  If you want the SCMI SMC based transport to operate in atomic

	  mode, avoiding any kind of sleeping behaviour for selected

	  transactions on the TX path, answer Y.

	  Enabling atomic mode operations allows any SCMI driver using this

	  transport to optionally ask for atomic SCMI transactions and operate

	  in atomic context too, at the price of using a number of busy-waiting

	  primitives all over instead. If unsure say N.



config ARM_SCMI_TRANSPORT_VIRTIO

	bool "SCMI transport based on VirtIO"

	depends on VIRTIO=y || VIRTIO=ARM_SCMI_PROTOCOL

drivers/firmware/arm_scmi/smc.c

+50 −6
Original line number Diff line number Diff line
@@ -7,6 +7,7 @@ 
 */



#include <linux/arm-smccc.h>

#include <linux/atomic.h>

#include <linux/device.h>

#include <linux/err.h>

#include <linux/interrupt.h>
@@ -14,6 +15,7 @@ 
#include <linux/of.h>

#include <linux/of_address.h>

#include <linux/of_irq.h>

#include <linux/processor.h>

#include <linux/slab.h>



#include "common.h"
@@ -23,14 +25,20 @@ 
 *

 * @cinfo: SCMI channel info

 * @shmem: Transmit/Receive shared memory area

 * @shmem_lock: Lock to protect access to Tx/Rx shared memory area

 * @shmem_lock: Lock to protect access to Tx/Rx shared memory area.

 *		Used when NOT operating in atomic mode.

 * @inflight: Atomic flag to protect access to Tx/Rx shared memory area.

 *	      Used when operating in atomic mode.

 * @func_id: smc/hvc call function id

 */



struct scmi_smc {

	struct scmi_chan_info *cinfo;

	struct scmi_shared_mem __iomem *shmem;

	/* Protect access to shmem area */

	struct mutex shmem_lock;

#define INFLIGHT_NONE	MSG_TOKEN_MAX

	atomic_t inflight;

	u32 func_id;

};
@@ -54,6 +62,41 @@ static bool smc_chan_available(struct device *dev, int idx) 
	return true;

}



static inline void smc_channel_lock_init(struct scmi_smc *scmi_info)

{

	if (IS_ENABLED(CONFIG_ARM_SCMI_TRANSPORT_SMC_ATOMIC_ENABLE))

		atomic_set(&scmi_info->inflight, INFLIGHT_NONE);

	else

		mutex_init(&scmi_info->shmem_lock);

}



static bool smc_xfer_inflight(struct scmi_xfer *xfer, atomic_t *inflight)

{

	int ret;



	ret = atomic_cmpxchg(inflight, INFLIGHT_NONE, xfer->hdr.seq);



	return ret == INFLIGHT_NONE;

}



static inline void

smc_channel_lock_acquire(struct scmi_smc *scmi_info,

			 struct scmi_xfer *xfer __maybe_unused)

{

	if (IS_ENABLED(CONFIG_ARM_SCMI_TRANSPORT_SMC_ATOMIC_ENABLE))

		spin_until_cond(smc_xfer_inflight(xfer, &scmi_info->inflight));

	else

		mutex_lock(&scmi_info->shmem_lock);

}



static inline void smc_channel_lock_release(struct scmi_smc *scmi_info)

{

	if (IS_ENABLED(CONFIG_ARM_SCMI_TRANSPORT_SMC_ATOMIC_ENABLE))

		atomic_set(&scmi_info->inflight, INFLIGHT_NONE);

	else

		mutex_unlock(&scmi_info->shmem_lock);

}



static int smc_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,

			  bool tx)

{
@@ -114,7 +157,7 @@ static int smc_chan_setup(struct scmi_chan_info *cinfo, struct device *dev, 


	scmi_info->func_id = func_id;

	scmi_info->cinfo = cinfo;

	mutex_init(&scmi_info->shmem_lock);

	smc_channel_lock_init(scmi_info);

	cinfo->transport_info = scmi_info;



	return 0;
@@ -140,10 +183,10 @@ static int smc_send_message(struct scmi_chan_info *cinfo, 
	struct arm_smccc_res res;



	/*

	 * Channel lock will be released only once response has been

	 * Channel will be released only once response has been

	 * surely fully retrieved, so after .mark_txdone()

	 */

	mutex_lock(&scmi_info->shmem_lock);

	smc_channel_lock_acquire(scmi_info, xfer);



	shmem_tx_prepare(scmi_info->shmem, xfer);
@@ -151,7 +194,7 @@ static int smc_send_message(struct scmi_chan_info *cinfo, 


	/* Only SMCCC_RET_NOT_SUPPORTED is valid error code */

	if (res.a0) {

		mutex_unlock(&scmi_info->shmem_lock);

		smc_channel_lock_release(scmi_info);

		return -EOPNOTSUPP;

	}
@@ -170,7 +213,7 @@ static void smc_mark_txdone(struct scmi_chan_info *cinfo, int ret) 
{

	struct scmi_smc *scmi_info = cinfo->transport_info;



	mutex_unlock(&scmi_info->shmem_lock);

	smc_channel_lock_release(scmi_info);

}



static const struct scmi_transport_ops scmi_smc_ops = {
@@ -196,4 +239,5 @@ const struct scmi_desc scmi_smc_desc = { 
	 * from the shared memory area.

	 */

	.sync_cmds_completed_on_ret = true,

	.atomic_enabled = IS_ENABLED(CONFIG_ARM_SCMI_TRANSPORT_SMC_ATOMIC_ENABLE),

};