From: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Date: Sun, 3 Feb 2019 15:17:30 +0000 (+0100)
Subject: rockchip: spi: only wait for completion, if transmitting
X-Git-Url: http://git.dujemihanovic.xyz/%22/img/sics.gif/%22/static/git-favicon.png?a=commitdiff_plain;h=7e0e5c552f2afcb9b6eeb2836232dfc4bbe29865;p=u-boot.git

rockchip: spi: only wait for completion, if transmitting

The logic in the main transmit loop took a bit of reading the TRM to
fully understand (due to silent assumptions based in internal logic):
the "wait until idle" at the end of each iteration through the loop is
required for the transmit-path as each clearing of the ENA register
(to update run-length in the CTRLR1 register) will implicitly flush
the FIFOs... transmisson can therefore not overlap loop iterations.

This change adds a comment to clarify the reason/need for waiting
until the controller becomes idle and wraps the entire check into an
'if (out)' to make it clear that this is required for transfers with a
transmit-component only (for transfers having a receive-component,
completion of the transmit-side is trivially ensured by having
received the correct number of bytes).

The change does not increase execution time measurably in any of my
tests.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
---

diff --git a/drivers/spi/rk_spi.c b/drivers/spi/rk_spi.c
index aaf244d426..c807d78185 100644
--- a/drivers/spi/rk_spi.c
+++ b/drivers/spi/rk_spi.c
@@ -379,9 +379,18 @@ static int rockchip_spi_xfer(struct udevice *dev, unsigned int bitlen,
 				toread--;
 			}
 		}
-		ret = rkspi_wait_till_not_busy(regs);
-		if (ret)
-			break;
+
+		/*
+		 * In case that there's a transmit-component, we need to wait
+		 * until the control goes idle before we can disable the SPI
+		 * control logic (as this will implictly flush the FIFOs).
+		 */
+		if (out) {
+			ret = rkspi_wait_till_not_busy(regs);
+			if (ret)
+				break;
+		}
+
 		len -= todo;
 	}