[PATCH v5 3/4] tpm: tpm_tis_spi: Introduce a flow control callback

[Stephen Boyd <swboyd@chromium.org>]

Cr50 firmware has a different flow control protocol than the one used by
this TPM PTP SPI driver. Introduce a flow control callback so we can
override the standard sequence with the custom one that Cr50 uses.

Cc: Andrey Pronin <apronin@chromium.org>
Cc: Duncan Laurie <dlaurie@chromium.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Guenter Roeck <groeck@chromium.org>
Cc: Alexander Steffen <Alexander.Steffen@infineon.com>
Cc: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
---
 drivers/char/tpm/tpm_tis_spi.c | 62 ++++++++++++++++++++++------------
 1 file changed, 41 insertions(+), 21 deletions(-)

diff --git a/drivers/char/tpm/tpm_tis_spi.c b/drivers/char/tpm/tpm_tis_spi.c
index 19513e622053..b3ed85671dd8 100644
--- a/drivers/char/tpm/tpm_tis_spi.c
+++ b/drivers/char/tpm/tpm_tis_spi.c
@@ -42,6 +42,8 @@
 struct tpm_tis_spi_phy {
 	struct tpm_tis_data priv;
 	struct spi_device *spi_device;
+	int (*flow_control)(struct tpm_tis_spi_phy *phy,
+			    struct spi_transfer *xfer);
 	u8 *iobuf;
 };
 
@@ -50,12 +52,46 @@ static inline struct tpm_tis_spi_phy *to_tpm_tis_spi_phy(struct tpm_tis_data *da
 	return container_of(data, struct tpm_tis_spi_phy, priv);
 }
 
+/*
+ * TCG SPI flow control is documented in section 6.4 of the spec[1]. In short,
+ * keep trying to read from the device until MISO goes high indicating the
+ * wait state has ended.
+ *
+ * [1] https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/
+ */
+static int tpm_tis_spi_flow_control(struct tpm_tis_spi_phy *phy,
+				    struct spi_transfer *spi_xfer)
+{
+	struct spi_message m;
+	int ret, i;
+
+	if ((phy->iobuf[3] & 0x01) == 0) {
+		// handle SPI wait states
+		phy->iobuf[0] = 0;
+
+		for (i = 0; i < TPM_RETRY; i++) {
+			spi_xfer->len = 1;
+			spi_message_init(&m);
+			spi_message_add_tail(spi_xfer, &m);
+			ret = spi_sync_locked(phy->spi_device, &m);
+			if (ret < 0)
+				return ret;
+			if (phy->iobuf[0] & 0x01)
+				break;
+		}
+
+		if (i == TPM_RETRY)
+			return -ETIMEDOUT;
+	}
+
+	return 0;
+}
+
 static int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u16 len,
 				u8 *in, const u8 *out)
 {
 	struct tpm_tis_spi_phy *phy = to_tpm_tis_spi_phy(data);
 	int ret = 0;
-	int i;
 	struct spi_message m;
 	struct spi_transfer spi_xfer;
 	u8 transfer_len;
@@ -82,26 +118,9 @@ static int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u16 len,
 		if (ret < 0)
 			goto exit;
 
-		if ((phy->iobuf[3] & 0x01) == 0) {
-			// handle SPI wait states
-			phy->iobuf[0] = 0;
-
-			for (i = 0; i < TPM_RETRY; i++) {
-				spi_xfer.len = 1;
-				spi_message_init(&m);
-				spi_message_add_tail(&spi_xfer, &m);
-				ret = spi_sync_locked(phy->spi_device, &m);
-				if (ret < 0)
-					goto exit;
-				if (phy->iobuf[0] & 0x01)
-					break;
-			}
-
-			if (i == TPM_RETRY) {
-				ret = -ETIMEDOUT;
-				goto exit;
-			}
-		}
+		ret = phy->flow_control(phy, &spi_xfer);
+		if (ret < 0)
+			goto exit;
 
 		spi_xfer.cs_change = 0;
 		spi_xfer.len = transfer_len;
@@ -207,6 +226,7 @@ static int tpm_tis_spi_probe(struct spi_device *dev)
 	phy->iobuf = devm_kmalloc(&dev->dev, MAX_SPI_FRAMESIZE, GFP_KERNEL);
 	if (!phy->iobuf)
 		return -ENOMEM;
+	phy->flow_control = tpm_tis_spi_flow_control;
 
 	/* If the SPI device has an IRQ then use that */
 	if (dev->irq > 0)
-- 
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