crypto: ccp - module parameter to limit the number of enabled CCPs

Provide the ability to constrain the total number of enabled devices in
the system. Once max_devs devices have been configured, subsequently
probed devices are ignored.

The max_devs parameter may be zero, in which case all CCPs are disabled.
PSPs are always enabled and active.

Disabling the CCPs also disables DMA and RNG registration.
Signed-off-by: Gary R Hook <gary.hook@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/ccp/ccp-dev.c

@@ -2,7 +2,7 @@
 /*
  * AMD Cryptographic Coprocessor (CCP) driver
  *
- * Copyright (C) 2013,2017 Advanced Micro Devices, Inc.
+ * Copyright (C) 2013,2019 Advanced Micro Devices, Inc.
  *
  * Author: Tom Lendacky <thomas.lendacky@amd.com>
  * Author: Gary R Hook <gary.hook@amd.com>
@@ -20,6 +20,7 @@
 #include <linux/delay.h>
 #include <linux/hw_random.h>
 #include <linux/cpu.h>
+#include <linux/atomic.h>
 #ifdef CONFIG_X86
 #include <asm/cpu_device_id.h>
 #endif
@@ -27,11 +28,19 @@
 
 #include "ccp-dev.h"
 
+#define MAX_CCPS 32
+
 /* Limit CCP use to a specifed number of queues per device */
 static unsigned int nqueues = 0;
 module_param(nqueues, uint, 0444);
 MODULE_PARM_DESC(nqueues, "Number of queues per CCP (minimum 1; default: all available)");
 
+/* Limit the maximum number of configured CCPs */
+static atomic_t dev_count = ATOMIC_INIT(0);
+static unsigned int max_devs = MAX_CCPS;
+module_param(max_devs, uint, 0444);
+MODULE_PARM_DESC(max_devs, "Maximum number of CCPs to enable (default: all; 0 disables all CCPs)");
+
 struct ccp_tasklet_data {
 	struct completion completion;
 	struct ccp_cmd *cmd;
@@ -592,6 +601,13 @@ int ccp_dev_init(struct sp_device *sp)
 	struct ccp_device *ccp;
 	int ret;
 
+	/*
+	 * Check how many we have so far, and stop after reaching
+	 * that number
+	 */
+	if (atomic_inc_return(&dev_count) > max_devs)
+		return 0; /* don't fail the load */
+
 	ret = -ENOMEM;
 	ccp = ccp_alloc_struct(sp);
 	if (!ccp)