From 940ec770c295682993d1cccce3081fd7c74fece8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Rafa=C5=82=20Mi=C5=82ecki?= <rafal@milecki.pl>
Date: Thu, 11 Oct 2018 09:42:17 +0200
Subject: [PATCH] spi: bcm-qspi: switch back to reading flash using smaller chunks
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Git-commit: 940ec770c295682993d1cccce3081fd7c74fece8
Patch-mainline: v4.20-rc1
References: bsc#1051510

Fixing/optimizing bcm_qspi_bspi_read() performance introduced two
Changes: 
1) It added a loop to read all requested data using multiple BSPI ops.
2) It bumped max size of a single BSPI block request from 256 to 512 B.

The later change resulted in occasional BSPI timeouts causing a
regression.

For some unknown reason hardware doesn't always handle reads as expected
when using 512 B chunks. In such cases it may happen that BSPI returns
amount of requested bytes without the last 1-3 ones. It provides the
remaining bytes later but doesn't raise an interrupt until another LR
start.

Switching back to 256 B reads fixes that problem and regression.

Fixes: 345309fa7c0c ("spi: bcm-qspi: Fix bcm_qspi_bspi_read() performance")
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/spi/spi-bcm-qspi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/spi/spi-bcm-qspi.c b/drivers/spi/spi-bcm-qspi.c
index eb3d67f01e8c..584bcb018a62 100644
--- a/drivers/spi/spi-bcm-qspi.c
+++ b/drivers/spi/spi-bcm-qspi.c
@@ -89,7 +89,7 @@
 #define BSPI_BPP_MODE_SELECT_MASK		BIT(8)
 #define BSPI_BPP_ADDR_SELECT_MASK		BIT(16)
 
-#define BSPI_READ_LENGTH			512
+#define BSPI_READ_LENGTH			256
 
 /* MSPI register offsets */
 #define MSPI_SPCR0_LSB				0x000
-- 
2.19.1