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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Mark Brown <broonie@kernel.org>,
        Akinobu Mita <akinobu.mita@gmail.com>,
        Sasha Levin <alexander.levin@microsoft.com>
Subject: [PATCH 4.4 032/134] spi: omap2-mcspi: poll OMAP2_MCSPI_CHSTAT_RXS for PIO transfer
Date:   Mon, 19 Mar 2018 19:05:15 +0100
Message-Id: <20180319171853.917407502@linuxfoundation.org>
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4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Akinobu Mita <akinobu.mita@gmail.com>


[ Upstream commit 812613591cb652344186c4cd912304ed02138566 ]

When running the spi-loopback-test with slower clock rate like 10 KHz,
the test for 251 bytes transfer was failed.  This failure triggered an
spi-omap2-mcspi's error message "DMA RX last word empty".

This message means that PIO for reading the remaining bytes due to the
DMA transfer length reduction is failed.  This problem can be fixed by
polling OMAP2_MCSPI_CHSTAT_RXS bit in channel status register to wait
until the receive buffer register is filled.

Cc: Mark Brown <broonie@kernel.org>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/spi/spi-omap2-mcspi.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

--- a/drivers/spi/spi-omap2-mcspi.c
+++ b/drivers/spi/spi-omap2-mcspi.c
@@ -457,6 +457,8 @@ omap2_mcspi_rx_dma(struct spi_device *sp
 	int			elements = 0;
 	int			word_len, element_count;
 	struct omap2_mcspi_cs	*cs = spi->controller_state;
+	void __iomem		*chstat_reg = cs->base + OMAP2_MCSPI_CHSTAT0;
+
 	mcspi = spi_master_get_devdata(spi->master);
 	mcspi_dma = &mcspi->dma_channels[spi->chip_select];
 	count = xfer->len;
@@ -517,8 +519,8 @@ omap2_mcspi_rx_dma(struct spi_device *sp
 	if (l & OMAP2_MCSPI_CHCONF_TURBO) {
 		elements--;
 
-		if (likely(mcspi_read_cs_reg(spi, OMAP2_MCSPI_CHSTAT0)
-				   & OMAP2_MCSPI_CHSTAT_RXS)) {
+		if (!mcspi_wait_for_reg_bit(chstat_reg,
+					    OMAP2_MCSPI_CHSTAT_RXS)) {
 			u32 w;
 
 			w = mcspi_read_cs_reg(spi, OMAP2_MCSPI_RX0);
@@ -536,8 +538,7 @@ omap2_mcspi_rx_dma(struct spi_device *sp
 			return count;
 		}
 	}
-	if (likely(mcspi_read_cs_reg(spi, OMAP2_MCSPI_CHSTAT0)
-				& OMAP2_MCSPI_CHSTAT_RXS)) {
+	if (!mcspi_wait_for_reg_bit(chstat_reg, OMAP2_MCSPI_CHSTAT_RXS)) {
 		u32 w;
 
 		w = mcspi_read_cs_reg(spi, OMAP2_MCSPI_RX0);