Change in coreboot[master]: drivers/spi/spi-generic: document SPI_CNTRLR_DEDUCT_CMD_LEN better

[Felix Held (Code Review)]

Felix Held has uploaded this change for review. ( https://review.coreboot.org/c/coreboot/+/60122 )

Change subject: drivers/spi/spi-generic: document SPI_CNTRLR_DEDUCT_CMD_LEN better
......................................................................

drivers/spi/spi-generic: document SPI_CNTRLR_DEDUCT_CMD_LEN better

This should make it a bit clearer what the differences between
SPI_CNTRLR_DEDUCT_OPCODE_LEN and SPI_CNTRLR_DEDUCT_CMD_LEN and the
corresponding functionality in spi_crop_chunk are.

Signed-off-by: Felix Held 
Change-Id: I809adebb182fc0866b93372b5b486117176da388
---
M src/drivers/spi/spi-generic.c
M src/include/spi-generic.h
2 files changed, 6 insertions(+), 1 deletion(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/22/60122/1

diff --git a/src/drivers/spi/spi-generic.c b/src/drivers/spi/spi-generic.c
index 9796663..e6ec7bd 100644
--- a/src/drivers/spi/spi-generic.c
+++ b/src/drivers/spi/spi-generic.c
@@ -98,6 +98,10 @@
    if (deduct_opcode_len)
    	cmd_len--;

+	/* Subtract command length from useable buffer size. If
+	   deduct_opcode_len is set, only subtract the number command bytes
+	   after the opcode. If the adjusted cmd_len is larger than ctrlr_max
+	   return 0 to inidicate an error. */
    if (deduct_cmd_len) {
    	if (ctrlr_max >= cmd_len) {
    		ctrlr_max -= cmd_len;
diff --git a/src/include/spi-generic.h b/src/include/spi-generic.h
index 77a3c09..acb22ec 100644
--- a/src/include/spi-generic.h
+++ b/src/include/spi-generic.h
@@ -111,7 +111,8 @@

enum {
    /* Deduct the command length from the spi_crop_chunk() calculation for
-	   sizing a transaction. */
+	   sizing a transaction. If SPI_CNTRLR_DEDUCT_OPCODE_LEN is set, only
+	   the bytes after the command byte will be deducted. */
    SPI_CNTRLR_DEDUCT_CMD_LEN = 1 << 0,
    /* Remove the opcode size from the command length used in the
       spi_crop_chunk() calculation. Controllers which have a dedicated