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Subject: Re: [PATCH v2] i2c: tegra: Create i2c_writesl_vi() to use with VI I2C
 for filling TX FIFO
To:     Sowjanya Komatineni <skomatineni@nvidia.com>,
        thierry.reding@gmail.com, jonathanh@nvidia.com, wsa@the-dreams.de
Cc:     linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-i2c@vger.kernel.org
References: <1610424379-23653-1-git-send-email-skomatineni@nvidia.com>
 <1610424379-23653-2-git-send-email-skomatineni@nvidia.com>
From:   Dmitry Osipenko <digetx@gmail.com>
Message-ID: <ae886d28-ef6c-63d3-2cc7-90752ddb8b21@gmail.com>
Date:   Tue, 12 Jan 2021 08:56:38 +0300
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12.01.2021 07:06, Sowjanya Komatineni пишет:
> 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@nvidia.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;
>  	}
> 

Looks almost good, could we please use a relaxed writel and avoid the casting in the code?

Like this:

diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
index 6f08c0c3238d..4f843b423d83 100644
--- a/drivers/i2c/busses/i2c-tegra.c
+++ b/drivers/i2c/busses/i2c-tegra.c
@@ -326,6 +326,8 @@ static void i2c_writel(struct tegra_i2c_dev *i2c_dev, u32 val, unsigned int reg)
 	/* read back register to make sure that register writes completed */
 	if (reg != I2C_TX_FIFO)
 		readl_relaxed(i2c_dev->base + tegra_i2c_reg_addr(i2c_dev, reg));
+	else
+		readl_relaxed(i2c_dev->base + tegra_i2c_reg_addr(i2c_dev, I2C_INT_STATUS));
 }
 
 static u32 i2c_readl(struct tegra_i2c_dev *i2c_dev, unsigned int reg)
@@ -339,6 +341,21 @@ 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, void *data,
+			   unsigned int reg, unsigned int len)
+{
+	u32 *data32 = data;
+
+	/*
+	 * 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. Each write to FIFO should follow by a read
+	 * of any I2C register in order to work around the problem.
+	 */
+	while (len--)
+		i2c_writel(i2c_dev, *data32++, reg);
+}
+
 static void i2c_readsl(struct tegra_i2c_dev *i2c_dev, void *data,
 		       unsigned int reg, unsigned int len)
 {
@@ -811,7 +828,10 @@ 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, 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;
 	}