spi_flash: Differentiate between atomic/manual sequencing

This adds a wrapper function and a Kconfig variable to differentiate
between SPI controllers which use atomic cycle sequencing versus
those where the transaction sequence is controlled manually. Currently
this boils down to x86 vs. non-x86.

Yes, it's hideous. The current API only worked because, for better or
worse, x86 platforms have been homogeneous in this regard since they
started using SPI as an alternative to FWH for boot flash. Now that
we have non-x86 platforms which use general purpose SPI controllers,
we should overhaul the entire SPI infrastructure to be more adaptable.

BUG=none
BRANCH=none
TEST=tested on nyan and link
Signed-off-by: David Hendricks <dhendrix@chromium.org>

Original-Change-Id: If8ccc9400a9d04772a195941a42bc82d5ecc1958
Original-Reviewed-on: https://chromium-review.googlesource.com/195283
Original-Reviewed-by: David Hendricks <dhendrix@chromium.org>
Original-Commit-Queue: David Hendricks <dhendrix@chromium.org>
Original-Tested-by: David Hendricks <dhendrix@chromium.org>
(cherry picked from commit 4170c59d06206667755402712083452da9fcd941)
Signed-off-by: Marc Jones <marc.jones@se-eng.com>

Change-Id: I54e2d3d9f9a0153a56f7a51b80f6ee6d997ad358
Reviewed-on: http://review.coreboot.org/7828
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

2 files changed, 54 insertions, 3 deletions

diff --git a/src/drivers/spi/Kconfig b/src/drivers/spi/Kconfig
index f96bf9f88b..cc8703f3fb 100644
--- a/src/drivers/spi/Kconfig
+++ b/src/drivers/spi/Kconfig
@@ -26,6 +26,16 @@ config SPI_FLASH
 
 if SPI_FLASH
 
+config SPI_ATOMIC_SEQUENCING
+	bool
+	default y if ARCH_X86
+	default n if !ARCH_X86
+	help
+	  Select this option if the SPI controller uses "atomic sequencing."
+	  Atomic sequencing is when the sequence of commands is pre-programmed
+	  in the SPI controller. Hardware manages the transaction instead of
+	  software. This is common on x86 platforms.
+
 config SPI_FLASH_MEMORY_MAPPED
 	bool
 	default y if ARCH_X86
diff --git a/src/drivers/spi/spi_flash.c b/src/drivers/spi/spi_flash.c
index de19b2ba06..0d67c43385 100644
--- a/src/drivers/spi/spi_flash.c
+++ b/src/drivers/spi/spi_flash.c
@@ -25,9 +25,50 @@ static void spi_flash_addr(u32 addr, u8 *cmd)
 	cmd[3] = addr >> 0;
 }
 
+/*
+ * If atomic sequencing is used, the cycle type is known to the SPI
+ * controller so that it can perform consecutive transfers and arbitrate
+ * automatically. Otherwise the SPI controller transfers whatever the
+ * user requests immediately, without regard to sequence. Atomic
+ * sequencing is commonly used on x86 platforms.
+ *
+ * SPI flash commands are simple two-step sequences. The command byte is
+ * always written first and may be followed by an address. Then data is
+ * either read or written. For atomic sequencing we'll pass everything into
+ * spi_xfer() at once and let the controller handle the details. Otherwise
+ * we will write all output bytes first and then read if necessary.
+ *
+ * FIXME: This really should be abstracted better, but that will
+ * require overhauling the entire SPI infrastructure.
+ */
+static int do_spi_flash_cmd(struct spi_slave *spi, const void *dout,
+		unsigned int bytes_out, void *din, unsigned int bytes_in)
+{
+	int ret = 1;
+
+#if CONFIG_SPI_ATOMIC_SEQUENCING == 1
+	if (spi_xfer(spi, dout, bytes_out, din, bytes_in) < 0)
+		goto done;
+#else
+	if (dout && bytes_out) {
+		if (spi_xfer(spi, dout, bytes_out, NULL, 0) < 0)
+			goto done;
+	}
+
+	if (din && bytes_in) {
+		if (spi_xfer(spi, NULL, 0, din, bytes_in) < 0)
+			goto done;
+	}
+#endif
+
+	ret = 0;
+done:
+	return ret;
+}
+
 int spi_flash_cmd(struct spi_slave *spi, u8 cmd, void *response, size_t len)
 {
-	int ret = spi_xfer(spi, &cmd, sizeof(cmd), response, len);
+	int ret = do_spi_flash_cmd(spi, &cmd, sizeof(cmd), response, len);
 	if (ret)
 		printk(BIOS_WARNING, "SF: Failed to send command %02x: %d\n", cmd, ret);
 
@@ -37,7 +78,7 @@ int spi_flash_cmd(struct spi_slave *spi, u8 cmd, void *response, size_t len)
 int spi_flash_cmd_read(struct spi_slave *spi, const u8 *cmd,
 		size_t cmd_len, void *data, size_t data_len)
 {
-	int ret = spi_xfer(spi, cmd, cmd_len, data, data_len);
+	int ret = do_spi_flash_cmd(spi, cmd, cmd_len, data, data_len);
 	if (ret) {
 		printk(BIOS_WARNING, "SF: Failed to send read command (%zu bytes): %d\n",
 				data_len, ret);
@@ -54,7 +95,7 @@ int spi_flash_cmd_write(struct spi_slave *spi, const u8 *cmd, size_t cmd_len,
 	memcpy(buff, cmd, cmd_len);
 	memcpy(buff + cmd_len, data, data_len);
 
-	ret = spi_xfer(spi, buff, cmd_len + data_len, NULL, 0);
+	ret = do_spi_flash_cmd(spi, buff, cmd_len + data_len, NULL, 0);
 	if (ret) {
 		printk(BIOS_WARNING, "SF: Failed to send write command (%zu bytes): %d\n",
 				data_len, ret);