linux-kernel - [PATCH v2] i2c: tegra: Create i2c_writesl_vi() to use with VI I2C for filling TX FIFO

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Date:   Mon, 11 Jan 2021 20:06:19 -0800
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     <thierry.reding@...il.com>, <jonathanh@...dia.com>,
        <digetx@...il.com>, <wsa@...-dreams.de>, <skomatineni@...dia.com>
CC:     <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-i2c@...r.kernel.org>
Subject: [PATCH v2] i2c: tegra: Create i2c_writesl_vi() to use with VI I2C for filling TX FIFO

VI I2C don't have DMA support and uses PIO mode all the time.

Current driver uses writesl() to fill TX FIFO based on available
empty slots and with this seeing strange silent hang during any I2C
register access after filling TX FIFO with 8 words.

Using writel() followed by i2c_readl() in a loop to write all words
to TX FIFO instead of using writesl() helps for large transfers in
PIO mode.

So, this patch creates i2c_writesl_vi() API to use with VI I2C for
filling TX FIFO.

Signed-off-by: Sowjanya Komatineni <skomatineni@...dia.com>
---
 drivers/i2c/busses/i2c-tegra.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
index 6f08c0c..e2b7503 100644
--- a/drivers/i2c/busses/i2c-tegra.c
+++ b/drivers/i2c/busses/i2c-tegra.c
@@ -339,6 +339,21 @@ static void i2c_writesl(struct tegra_i2c_dev *i2c_dev, void *data,
 	writesl(i2c_dev->base + tegra_i2c_reg_addr(i2c_dev, reg), data, len);
 }
 
+static void i2c_writesl_vi(struct tegra_i2c_dev *i2c_dev, u32 *data,
+			   unsigned int reg, unsigned int len)
+{
+	/*
+	 * Using writesl() to fill VI I2C TX FIFO for transfers more than
+	 * 6 words is causing a silent hang on any VI I2C register access
+	 * after TX FIFO writes.
+	 * So using writel() followed by i2c_readl().
+	 */
+	while (len--) {
+		writel(*data++, i2c_dev->base + tegra_i2c_reg_addr(i2c_dev, reg));
+		i2c_readl(i2c_dev, I2C_INT_STATUS);
+	}
+}
+
 static void i2c_readsl(struct tegra_i2c_dev *i2c_dev, void *data,
 		       unsigned int reg, unsigned int len)
 {
@@ -811,7 +826,10 @@ static int tegra_i2c_fill_tx_fifo(struct tegra_i2c_dev *i2c_dev)
 		i2c_dev->msg_buf_remaining = buf_remaining;
 		i2c_dev->msg_buf = buf + words_to_transfer * BYTES_PER_FIFO_WORD;
 
-		i2c_writesl(i2c_dev, buf, I2C_TX_FIFO, words_to_transfer);
+		if (i2c_dev->is_vi)
+			i2c_writesl_vi(i2c_dev, (u32 *)buf, I2C_TX_FIFO, words_to_transfer);
+		else
+			i2c_writesl(i2c_dev, buf, I2C_TX_FIFO, words_to_transfer);
 
 		buf += words_to_transfer * BYTES_PER_FIFO_WORD;
 	}
-- 
2.7.4