linux/arch/powerpc/mm/icswx.c

/*
 *  ICSWX and ACOP Management
 *
 *  Copyright (C) 2011 Anton Blanchard, IBM Corp. <anton@samba.org>
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; either version
 *  2 of the License, or (at your option) any later version.
 *
 */

#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/types.h>
#include <linux/mm.h>
#include <linux/spinlock.h>
#include <linux/module.h>
#include "icswx.h"

/*
 * The processor and its L2 cache cause the icswx instruction to
 * generate a COP_REQ transaction on PowerBus. The transaction has no
 * address, and the processor does not perform an MMU access to
 * authenticate the transaction. The command portion of the PowerBus
 * COP_REQ transaction includes the LPAR_ID (LPID) and the coprocessor
 * Process ID (PID), which the coprocessor compares to the authorized
 * LPID and PID held in the coprocessor, to determine if the process
 * is authorized to generate the transaction.  The data of the COP_REQ
 * transaction is 128-byte or less in size and is placed in cacheable
 * memory on a 128-byte cache line boundary.
 *
 * The task to use a coprocessor should use use_cop() to mark the use
 * of the Coprocessor Type (CT) and context switching. On a server
 * class processor, the PID register is used only for coprocessor
 * management + * and so a coprocessor PID is allocated before
 * executing icswx + * instruction. Drop_cop() is used to free the
 * coprocessor PID.
 *
 * Example:
 * Host Fabric Interface (HFI) is a PowerPC network coprocessor.
 * Each HFI have multiple windows. Each HFI window serves as a
 * network device sending to and receiving from HFI network.
 * HFI immediate send function uses icswx instruction. The immediate
 * send function allows small (single cache-line) packets be sent
 * without using the regular HFI send FIFO and doorbell, which are
 * much slower than immediate send.
 *
 * For each task intending to use HFI immediate send, the HFI driver
 * calls use_cop() to obtain a coprocessor PID for the task.
 * The HFI driver then allocate a free HFI window and save the
 * coprocessor PID to the HFI window to allow the task to use the
 * HFI window.
 *
 * The HFI driver repeatedly creates immediate send packets and
 * issues icswx instruction to send data through the HFI window.
 * The HFI compares the coprocessor PID in the CPU PID register
 * to the PID held in the HFI window to determine if the transaction
 * is allowed.
 *
 * When the task to release the HFI window, the HFI driver calls
 * drop_cop() to release the coprocessor PID.
 */

void switch_cop(struct mm_struct *next)
{
#ifdef CONFIG_ICSWX_PID
	mtspr(SPRN_PID, next->context.cop_pid);
#endif
	mtspr(SPRN_ACOP, next->context.acop);
}

/**
 * Start using a coprocessor.
 * @acop: mask of coprocessor to be used.
 * @mm: The mm the coprocessor to associate with. Most likely current mm.
 *
 * Return a positive PID if successful. Negative errno otherwise.
 * The returned PID will be fed to the coprocessor to determine if an
 * icswx transaction is authenticated.
 */
int use_cop(unsigned long acop, struct mm_struct *mm)
{
	int ret;

	if (!cpu_has_feature(CPU_FTR_ICSWX))
		return -ENODEV;

	if (!mm || !acop)
		return -EINVAL;

	/* The page_table_lock ensures mm_users won't change under us */
	spin_lock(&mm->page_table_lock);
	spin_lock(mm->context.cop_lockp);

	ret = get_cop_pid(mm);
	if (ret < 0)
		goto out;

	/* update acop */
	mm->context.acop |= acop;

	sync_cop(mm);

	/*
	 * If this is a threaded process then there might be other threads
	 * running. We need to send an IPI to force them to pick up any
	 * change in PID and ACOP.
	 */
	if (atomic_read(&mm->mm_users) > 1)
		smp_call_function(sync_cop, mm, 1);

out:
	spin_unlock(mm->context.cop_lockp);
	spin_unlock(&mm->page_table_lock);

	return ret;
}
EXPORT_SYMBOL_GPL(use_cop);

/**
 * Stop using a coprocessor.
 * @acop: mask of coprocessor to be stopped.
 * @mm: The mm the coprocessor associated with.
 */
void drop_cop(unsigned long acop, struct mm_struct *mm)
{
	int free_pid;

	if (!cpu_has_feature(CPU_FTR_ICSWX))
		return;

	if (WARN_ON_ONCE(!mm))
		return;

	/* The page_table_lock ensures mm_users won't change under us */
	spin_lock(&mm->page_table_lock);
	spin_lock(mm->context.cop_lockp);

	mm->context.acop &= ~acop;

	free_pid = disable_cop_pid(mm);
	sync_cop(mm);

	/*
	 * If this is a threaded process then there might be other threads
	 * running. We need to send an IPI to force them to pick up any
	 * change in PID and ACOP.
	 */
	if (atomic_read(&mm->mm_users) > 1)
		smp_call_function(sync_cop, mm, 1);

	if (free_pid != COP_PID_NONE)
		free_cop_pid(free_pid);

	spin_unlock(mm->context.cop_lockp);
	spin_unlock(&mm->page_table_lock);
}
EXPORT_SYMBOL_GPL(drop_cop);