Re: [PATCH] i2c: designware: evaluate i2c-sda-hold-time property

[Sascha Hauer <s.hauer@pengutronix.de>]

On Wed, Jan 10, 2018 at 08:52:02AM +0100, Steffen Trumtrar wrote:
> Newer designware i2c controllers allow setting the SDA hold time.
> Evaluate the devicetree property "i2c-sda-hold-time" and set the
> value accordingly.
> The code is an adaption of the Linux v4.12 driver.
> 
> Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
> ---
>  drivers/i2c/busses/i2c-designware.c | 40 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 40 insertions(+)

Applied, thanks

Sascha

> 
> diff --git a/drivers/i2c/busses/i2c-designware.c b/drivers/i2c/busses/i2c-designware.c
> index 0b022afd30f8..33f89148f0cc 100644
> --- a/drivers/i2c/busses/i2c-designware.c
> +++ b/drivers/i2c/busses/i2c-designware.c
> @@ -32,6 +32,7 @@
>  #include <xfuncs.h>
>  #include <linux/clk.h>
>  #include <linux/err.h>
> +#include <linux/math64.h>
>  
>  #include <io.h>
>  #include <i2c/i2c.h>
> @@ -75,6 +76,7 @@
>  #define DW_IC_TX_TL			0x3c
>  #define DW_IC_CLR_INTR			0x40
>  #define DW_IC_CLR_TX_ABRT		0x54
> +#define DW_IC_SDA_HOLD			0x7c
>  
>  #define DW_IC_ENABLE			0x6c
>  #define DW_IC_ENABLE_ENABLE		(1 << 0)
> @@ -90,6 +92,8 @@
>  #define DW_IC_ENABLE_STATUS		0x9c
>  #define DW_IC_ENABLE_STATUS_IC_EN	(1 << 0)
>  
> +#define DW_IC_COMP_VERSION		0xf8
> +#define DW_IC_SDA_HOLD_MIN_VERS		0x3131312A
>  #define DW_IC_COMP_TYPE			0xfc
>  #define DW_IC_COMP_TYPE_VALUE		0x44570140
>  
> @@ -99,10 +103,15 @@
>  #define DW_TIMEOUT_TX			(2 * MSECOND)
>  #define DW_TIMEOUT_RX			(2 * MSECOND)
>  
> +#define DW_IC_SDA_HOLD_RX_SHIFT		16
> +#define DW_IC_SDA_HOLD_RX_MASK		GENMASK(23, DW_IC_SDA_HOLD_RX_SHIFT)
> +
> +
>  struct dw_i2c_dev {
>  	void __iomem *base;
>  	struct clk *clk;
>  	struct i2c_adapter adapter;
> +	u32 sda_hold_time;
>  };
>  
>  static inline struct dw_i2c_dev *to_dw_i2c_dev(struct i2c_adapter *a)
> @@ -202,6 +211,7 @@ i2c_dw_scl_lcnt(uint32_t ic_clk, uint32_t tLOW, uint32_t tf, int offset)
>  static void i2c_dw_setup_timings(struct dw_i2c_dev *dw)
>  {
>  	uint32_t hcnt, lcnt;
> +	u32 reg;
>  
>  	const uint32_t sda_falling_time = 300; /* ns */
>  	const uint32_t scl_falling_time = 300; /* ns */
> @@ -234,6 +244,36 @@ static void i2c_dw_setup_timings(struct dw_i2c_dev *dw)
>  
>  	writel(hcnt, dw->base + DW_IC_FS_SCL_HCNT);
>  	writel(lcnt, dw->base + DW_IC_FS_SCL_LCNT);
> +
> +	/* Configure SDA Hold Time if required */
> +	reg = readl(dw->base + DW_IC_COMP_VERSION);
> +	if (reg >= DW_IC_SDA_HOLD_MIN_VERS) {
> +		u32 ht;
> +		int ret;
> +
> +		ret = of_property_read_u32(dw->adapter.dev.device_node,
> +					   "i2c-sda-hold-time-ns", &ht);
> +		if (ret) {
> +			/* Keep previous hold time setting if no one set it */
> +			dw->sda_hold_time = readl(dw->base + DW_IC_SDA_HOLD);
> +		} else if (ht) {
> +			dw->sda_hold_time = div_u64((u64)input_clock_khz * ht + 500000,
> +						    1000000);
> +		}
> +
> +		/*
> +		 * Workaround for avoiding TX arbitration lost in case I2C
> +		 * slave pulls SDA down "too quickly" after falling egde of
> +		 * SCL by enabling non-zero SDA RX hold. Specification says it
> +		 * extends incoming SDA low to high transition while SCL is
> +		 * high but it apprears to help also above issue.
> +		 */
> +		if (!(dw->sda_hold_time & DW_IC_SDA_HOLD_RX_MASK))
> +			dw->sda_hold_time |= 1 << DW_IC_SDA_HOLD_RX_SHIFT;
> +
> +		dev_dbg(&dw->adapter.dev, "adjust SDA hold time.\n");
> +		writel(dw->sda_hold_time, dw->base + DW_IC_SDA_HOLD);
> +	}
>  }
>  
>  static int i2c_dw_wait_for_bits(struct dw_i2c_dev *dw, uint32_t offset,
> -- 
> 2.11.0
> 
> 
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