ec/google/chromeec: Add minimum delay between SPI CS assertions

Some Chrome OS ECs require a small amount of time after a SPI
transaction to reset their controllers before they can service the next
CS assertion. The kernel and depthcharge have always enforced a 200us
minimum delay for this... coreboot should've done the same.

BRANCH=gru
BUG=chrome-os-partner:58046
TEST=Booted Kevin in recovery mode, confirmed that recovery events got
logged with correct timestamps in eventlog.

Change-Id: I32ec343f3293ac93729d3e6e2f43d7605a396cdb
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: b9e4696533d4318ae7c8715b71ab963d8897c16c
Original-Change-Id: I6a7baf7859d5d50e299495d118e7890dcaa2c1b0
Original-Signed-off-by: Julius Werner <jwerner@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/392206
Original-Tested-by: Shawn N <shawnn@chromium.org>
Original-Reviewed-by: Shawn N <shawnn@chromium.org>
Reviewed-on: https://review.coreboot.org/16885
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

1 files changed, 21 insertions, 11 deletions

diff --git a/src/ec/google/chromeec/ec_spi.c b/src/ec/google/chromeec/ec_spi.c
index e93d038213..a0049c6860 100644
--- a/src/ec/google/chromeec/ec_spi.c
+++ b/src/ec/google/chromeec/ec_spi.c
@@ -20,6 +20,11 @@
 #include <spi-generic.h>
 #include <timer.h>
 
+/* This is assuming that this driver is not used on x86. If that changes, this
+   might need to become a CAR_GLOBAL or maybe even more complicated. */
+static struct stopwatch cs_cooldown_sw;
+static const long cs_cooldown_us = 200;
+
 static const uint8_t EcFramingByte = 0xec;
 
 #define PROTO3_MAX_PACKET_SIZE 268
@@ -44,7 +49,10 @@ void *crosec_get_buffer(size_t size, int req)
 static int crosec_spi_io(size_t req_size, size_t resp_size, void *context)
 {
 	struct spi_slave *slave = (struct spi_slave *)context;
+	int ret = 0;
 
+	while (!stopwatch_expired(&cs_cooldown_sw))
+		/* Wait minimum delay between CS assertions. */;
 	spi_claim_bus(slave);
 
 	 /* Allow EC to ramp up clock after being awaken.
@@ -53,8 +61,8 @@ static int crosec_spi_io(size_t req_size, size_t resp_size, void *context)
 
 	if (spi_xfer(slave, req_buf, req_size, NULL, 0)) {
 		printk(BIOS_ERR, "%s: Failed to send request.\n", __func__);
-		spi_release_bus(slave);
-		return -1;
+		ret = -1;
+		goto out;
 	}
 
 	uint8_t byte;
@@ -65,8 +73,8 @@ static int crosec_spi_io(size_t req_size, size_t resp_size, void *context)
 		if (spi_xfer(slave, NULL, 0, &byte, sizeof(byte))) {
 			printk(BIOS_ERR, "%s: Failed to receive byte.\n",
 			       __func__);
-			spi_release_bus(slave);
-			return -1;
+			ret = -1;
+			goto out;
 		}
 		if (byte == EcFramingByte)
 			break;
@@ -75,28 +83,30 @@ static int crosec_spi_io(size_t req_size, size_t resp_size, void *context)
 			printk(BIOS_ERR,
 			       "%s: Timeout waiting for framing byte.\n",
 			       __func__);
-			spi_release_bus(slave);
-			return -1;
+			ret = -1;
+			goto out;
 		}
 	}
 
 	if (spi_xfer(slave, NULL, 0, resp_buf, resp_size)) {
 		printk(BIOS_ERR, "%s: Failed to receive response.\n", __func__);
-		spi_release_bus(slave);
-		return -1;
+		ret = -1;
 	}
 
+out:
 	spi_release_bus(slave);
-
-	return 0;
+	stopwatch_init_usecs_expire(&cs_cooldown_sw, cs_cooldown_us);
+	return ret;
 }
 
 int google_chromeec_command(struct chromeec_command *cec_command)
 {
 	static struct spi_slave *slave = NULL;
-	if (!slave)
+	if (!slave) {
 		slave = spi_setup_slave(CONFIG_EC_GOOGLE_CHROMEEC_SPI_BUS,
 					CONFIG_EC_GOOGLE_CHROMEEC_SPI_CHIP);
+		stopwatch_init(&cs_cooldown_sw);
+	}
 	return crosec_command_proto(cec_command, crosec_spi_io, slave);
 }