powerpc: Split ICSWX ACOP and PID processing

Some processors, like embedded, that already have a PID register that
is managed by the system.  This patch separates the ACOP and PID
processing into separate files so that the ACOP code can be shared.

Signed-off-by: Jimi Xenidis <jimix@pobox.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 160 insertions, 0 deletions

diff --git a/arch/powerpc/mm/icswx.c b/arch/powerpc/mm/icswx.c
new file mode 100644
index 0000000..a98850f
--- /dev/null
+++ b/arch/powerpc/mm/icswx.c
@@ -0,0 +1,160 @@
+/*
+ *  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);