cr50: use board prop to mask straps if config is ambiguous

Cr50 tries to determine SPI vs I2C by checking that there are pullups on
only the I2C or SPI straps. If there are pullups on both, it can't use
the straps to determine SPI vs I2C, so it just defaults to the default
board properties (I2C and PLT_RST_L).

This change uses last board properties to determine I2C vs SPI if the
straps can't be used to make this determination. The actual strap pins
are only connected to the pullup or pulldown being used for the straps.
It's pretty likely these strap readings are correct. The unused straps
are connected to the AP which can interfere with these readings if it
has a pullup on any of these signals. This change uses the last board
property configuration to determine I2C vs SPI and mask unused straps to
try and remove signals the AP is interfering with. If this masked config
isn't valid, then cr50 will still fall back to using I2C and PLT_RST_L.

BUG=b:124777847
BRANCH=cr50
TEST=manual
	flash mistral. Reboot cr50. Make sure it doesn't switch to I2C
	config
		# Verify cr50 selects spi
		Ambiguous strap config. Use spi based on old brdprop.

	Use DBG image to set invalid I2C and SPI board property settings
	rollback to the image that checks if I2C and SPI brdprop
	settings are invalid. Verify Mistral can't find a valid strap
	and uses I2C.

	Use DBG image to select SPI and I2C board properties. Make sure
	this is rejected as invalid.
		# enable writing to long life scratch 1
		rw 0x40000128 2

		# write old board properties with i2c and spi
		rw 0x40000130 (OLD_BRDPROP | 3)
		for mistral - rw 0x40000130 0x811143

		# rollback to image that checks old board properties if
		# straps are ambiguous
		rollback

		# Verify Mistral doesn't use old AP bus setting and
		# defaults to  the default properties.
		Invalid strap pins! Default properties = 0x42

	Use DBG image to select neither the SPI or I2C board property.
	Make sure this is rejected as invalid.
		# enable writing to long life scratch 1
		rw 0x40000128 2

		# write old board properties without i2c or spi
		rw 0x40000130 (OLD_BRDPROP & ~3)
		for mistral - rw 0x40000130 0x811140

		# rollback to image that checks old board properties if
		# straps are ambiguous
		rollback

		# Verify Mistral doesn't use old AP bus setting and
		# defaults to  the default properties.
		Invalid strap pins! Default properties = 0x42

	Use dbg image to modify board properties to select I2C. rollback
	and make sure Cr50 continues using I2C.
		# enable writing to long life scratch 1
		rw 0x40000128 2

		# write old board properties with i2c
		for mistral - rw 0x40000130 0x811142

		# write old board properties with i2c
		rollback

		# Verify cr50 selects i2c
		Ambiguous strap config. Use i2c based on old brdprop.

Change-Id: I409e2f3ab1339aafe450b35259adc3c4c5d870ae
Signed-off-by: Mary Ruthven <mruthven@google.com>
Reviewed-on: https://chromium-review.googlesource.com/1483816
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Mary Ruthven <mruthven@chromium.org>
Reviewed-by: Keith Short <keithshort@chromium.org>

1 files changed, 32 insertions, 6 deletions

diff --git a/board/cr50/board.c b/board/cr50/board.c
index 67908dc388..e7e19a4577 100644
--- a/board/cr50/board.c
+++ b/board/cr50/board.c
@@ -1206,8 +1206,10 @@ static int get_strap_config(uint8_t *config)
 	enum strap_list s0;
 	int lvl;
 	int flags;
-	uint8_t pull_a;
-	uint8_t pull_b;
+	uint8_t use_i2c;
+	uint8_t i2c_prop;
+	uint8_t use_spi;
+	uint8_t spi_prop;
 
 	/*
 	 * There are 4 pins that are used to determine Cr50 board strapping
@@ -1313,13 +1315,37 @@ static int get_strap_config(uint8_t *config)
 	 * config table entries.
 	 */
 
-	pull_a = *config & 0xa0;
-	pull_b = *config & 0xa;
-	if ((!pull_a && !pull_b) || (pull_a && pull_b))
+	use_i2c = *config & 0xa0;
+	use_spi = *config & 0x0a;
+	/*
+	 * The strap signals should have at least one pullup. Nothing can
+	 * interfere with these. If we did not read any pullups, these are
+	 * invalid straps. The config can't be salvaged.
+	 */
+	if (!use_i2c && !use_spi)
 		return EC_ERROR_INVAL;
+	/*
+	 * The unused strap signals are used for the bus to the AP. If the AP
+	 * has added pullups to the signals, it could interfere with the strap
+	 * readings. If pullups are found on both the SPI and I2C straps, use
+	 * the board properties to determine SPI vs I2C. We can use this to mask
+	 * unused config pins the AP is interfering with.
+	 */
+	if (use_i2c && use_spi) {
+		spi_prop = (GREG32(PMU, LONG_LIFE_SCRATCH1) &
+			    BOARD_SLAVE_CONFIG_SPI);
+		i2c_prop = (GREG32(PMU, LONG_LIFE_SCRATCH1) &
+			    BOARD_SLAVE_CONFIG_I2C);
+		/* Make sure exactly one interface is selected */
+		if ((i2c_prop && spi_prop) || (!spi_prop && !i2c_prop))
+			return EC_ERROR_INVAL;
+		use_spi = spi_prop;
+		CPRINTS("Ambiguous strap config. Use %s based on old "
+			"brdprop.", use_spi ? "spi" : "i2c");
+	}
 
 	/* Now that I2C vs SPI is known, mask the unused strap bits. */
-	*config &= *config & 0xa ? 0xf : 0xf0;
+	*config &= use_spi ? 0xf : 0xf0;
 
 	return EC_SUCCESS;
 }