[PATCH 3/4] fpga mgr: zynq: Add support for encrypted bitstreams

[Moritz Fischer]

Add new flag FPGA_MGR_DECRYPT_BISTREAM as well as a matching
capability FPGA_MGR_CAP_DECRYPT to allow for on-the-fly
decryption of an encrypted bitstream.

If the system is not booted in secure mode AES & HMAC units
are disabled by the boot ROM, therefore the capability
is not available.

Signed-off-by: Moritz Fischer <moritz.fischer@xxxxxxxxx>
Cc: Alan Tull <atull@xxxxxxxxxxxxxxxxxxxxx>
Cc: Michal Simek <michal.simek@xxxxxxxxxx>
Cc: SÃren Brinkmann <soren.brinkmann@xxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
---
 drivers/fpga/fpga-mgr.c       |  7 +++++++
 drivers/fpga/zynq-fpga.c      | 21 +++++++++++++++++++--
 include/linux/fpga/fpga-mgr.h |  2 ++
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/drivers/fpga/fpga-mgr.c b/drivers/fpga/fpga-mgr.c
index 98230b7..e4d08e1 100644
--- a/drivers/fpga/fpga-mgr.c
+++ b/drivers/fpga/fpga-mgr.c
@@ -61,6 +61,12 @@ int fpga_mgr_buf_load(struct fpga_manager *mgr, u32 flags, const char *buf,
 		return -ENOTSUPP;
 	}
 
+	if (flags & FPGA_MGR_DECRYPT_BITSTREAM &&
+	    !fpga_mgr_has_cap(FPGA_MGR_CAP_DECRYPT, mgr->caps)) {
+		dev_err(dev, "Bitstream decryption not supported\n");
+		return -ENOTSUPP;
+	}
+
 	/*
 	 * Call the low level driver's write_init function.  This will do the
 	 * device-specific things to get the FPGA into the state where it is
@@ -170,6 +176,7 @@ static const char * const state_str[] = {
 static const char * const cap_str[] = {
 	[FPGA_MGR_CAP_FULL_RECONF] = "Full reconfiguration",
 	[FPGA_MGR_CAP_PARTIAL_RECONF] = "Partial reconfiguration",
+	[FPGA_MGR_CAP_DECRYPT] = "Decrypt bitstream on the fly",
 };
 
 static ssize_t name_show(struct device *dev,
diff --git a/drivers/fpga/zynq-fpga.c b/drivers/fpga/zynq-fpga.c
index 1d37ff0..0aa4705 100644
--- a/drivers/fpga/zynq-fpga.c
+++ b/drivers/fpga/zynq-fpga.c
@@ -71,6 +71,10 @@
 #define CTRL_PCAP_PR_MASK		BIT(27)
 /* Enable PCAP */
 #define CTRL_PCAP_MODE_MASK		BIT(26)
+/* Needed to reduce clock rate for secure config */
+#define CTRL_PCAP_RATE_EN_MASK		BIT(25)
+/* System booted in secure mode */
+#define CTRL_SEC_EN_MASK		BIT(7)
 
 /* Miscellaneous Control Register bit definitions */
 /* Internal PCAP loopback */
@@ -252,12 +256,20 @@ static int zynq_fpga_ops_write_init(struct fpga_manager *mgr, u32 flags,
 
 	/* set configuration register with following options:
 	 * - enable PCAP interface
-	 * - set throughput for maximum speed
+	 * - set throughput for maximum speed (if we're not decrypting)
 	 * - set CPU in user mode
 	 */
 	ctrl = zynq_fpga_read(priv, CTRL_OFFSET);
-	zynq_fpga_write(priv, CTRL_OFFSET,
+	if (flags & FPGA_MGR_DECRYPT_BITSTREAM) {
+		zynq_fpga_write(priv, CTRL_OFFSET,
+			(CTRL_PCAP_PR_MASK | CTRL_PCAP_MODE_MASK |
+			 CTRL_PCAP_RATE_EN_MASK | ctrl));
+
+	} else {
+		ctrl &= ~CTRL_PCAP_RATE_EN_MASK;
+		zynq_fpga_write(priv, CTRL_OFFSET,
 			(CTRL_PCAP_PR_MASK | CTRL_PCAP_MODE_MASK | ctrl));
+	}
 
 	/* check that we have room in the command queue */
 	status = zynq_fpga_read(priv, STATUS_OFFSET);
@@ -412,6 +424,7 @@ static int zynq_fpga_probe(struct platform_device *pdev)
 	struct resource *res;
 	fpga_mgr_cap_mask_t caps;
 	int err;
+	u32 tmp;
 
 	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
 	if (!priv)
@@ -466,6 +479,10 @@ static int zynq_fpga_probe(struct platform_device *pdev)
 	fpga_mgr_cap_set(FPGA_MGR_CAP_FULL_RECONF, caps);
 	fpga_mgr_cap_set(FPGA_MGR_CAP_PARTIAL_RECONF, caps);
 
+	/* only works if we booted in secure mode */
+	tmp = zynq_fpga_read(priv, CTRL_OFFSET);
+	if (tmp & CTRL_SEC_EN_MASK)
+		fpga_mgr_cap_set(FPGA_MGR_CAP_DECRYPT, caps);
 
 	err = fpga_mgr_register(dev, "Xilinx Zynq FPGA Manager",
 				&zynq_fpga_ops, caps, priv);
diff --git a/include/linux/fpga/fpga-mgr.h b/include/linux/fpga/fpga-mgr.h
index 9bb96a5..aabe258 100644
--- a/include/linux/fpga/fpga-mgr.h
+++ b/include/linux/fpga/fpga-mgr.h
@@ -68,10 +68,12 @@ enum fpga_mgr_states {
  */
 #define FPGA_MGR_PARTIAL_RECONFIG	BIT(0)
 #define FPGA_MGR_FULL_RECONFIG		BIT(1)
+#define FPGA_MGR_DECRYPT_BITSTREAM	BIT(2)
 
 enum fpga_mgr_capability {
 	FPGA_MGR_CAP_PARTIAL_RECONF,
 	FPGA_MGR_CAP_FULL_RECONF,
+	FPGA_MGR_CAP_DECRYPT,
 
 /* last capability type for creation of the capabilities mask */
 	FPGA_MGR_CAP_END,
-- 
2.10.0