linux-kernel - Re: [PATCH REBASE] i2c-designware: make SDA hold time configurable

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Date:	Mon, 17 Jun 2013 15:55:30 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Christian Ruppert <christian.ruppert@...lis.com>
CC:	Wolfram Sang <wsa@...-dreams.de>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	linux-i2c@...r.kernel.org,
	"Ben Dooks (embedded platforms)" <ben-linux@...ff.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Landley <rob@...dley.net>,
	devicetree-discuss@...ts.ozlabs.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Vineet Gupta <Vineet.Gupta1@...opsys.com>,
	Pierrick Hascoet <pierrick.hascoet@...lis.com>
Subject: Re: [PATCH REBASE] i2c-designware: make SDA hold time configurable

On 05/14/2013 08:04 AM, Christian Ruppert wrote:
> This patch makes the SDA hold time configurable through device tree.
> 
> [rebased to i2c-current/i2c-next/mainline-3.10-rc1]
> 
> Signed-off-by: Christian Ruppert <christian.ruppert@...lis.com>
> Signed-off-by: Pierrick Hascoet <pierrick.hascoet@...lis.com>
> ---
>  .../devicetree/bindings/i2c/i2c-designware.txt     |   14 ++++++++++++++
>  drivers/i2c/busses/i2c-designware-core.c           |    5 +++++
>  drivers/i2c/busses/i2c-designware-core.h           |    1 +
>  drivers/i2c/busses/i2c-designware-platdrv.c        |    9 +++++++++
>  4 files changed, 29 insertions(+), 0 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/i2c/i2c-designware.txt b/Documentation/devicetree/bindings/i2c/i2c-designware.txt
> index e42a2ee..21fabe7 100644
> --- a/Documentation/devicetree/bindings/i2c/i2c-designware.txt
> +++ b/Documentation/devicetree/bindings/i2c/i2c-designware.txt
> @@ -10,6 +10,9 @@ Recommended properties :
>  
>   - clock-frequency : desired I2C bus clock frequency in Hz.
>  
> +Optional properties :
> + - sda-hold-time : should contain the SDA hold time in nanoseconds.

Please specify time units in the property name. Perhaps
i2c-sda-hold-time-ns.

Based on reading the discussion, there is one similar property I have
found: "samsung,i2c-sda-delay = <100>". I wouldn't copy it as it doesn't
tell the units or what the delay is.

Otherwise, looks fine to me.

Rob

> +
>  Example :
>  
>  	i2c@...00 {
> @@ -20,3 +23,14 @@ Example :
>  		interrupts = <11>;
>  		clock-frequency = <400000>;
>  	};
> +
> +	i2c@...0000 {
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +		compatible = "snps,designware-i2c";
> +		reg = <0x1120000 0x1000>;
> +		interrupt-parent = <&ictl>;
> +		interrupts = <12 1>;
> +		clock-frequency = <400000>;
> +		sda-hold-time = <300>;
> +	};
> diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c
> index 21fbb34..91d422c 100644
> --- a/drivers/i2c/busses/i2c-designware-core.c
> +++ b/drivers/i2c/busses/i2c-designware-core.c
> @@ -67,6 +67,7 @@
>  #define DW_IC_STATUS		0x70
>  #define DW_IC_TXFLR		0x74
>  #define DW_IC_RXFLR		0x78
> +#define DW_IC_SDA_HOLD		0x7c
>  #define DW_IC_TX_ABRT_SOURCE	0x80
>  #define DW_IC_ENABLE_STATUS	0x9c
>  #define DW_IC_COMP_PARAM_1	0xf4
> @@ -332,6 +333,10 @@ int i2c_dw_init(struct dw_i2c_dev *dev)
>  	dw_writel(dev, lcnt, DW_IC_FS_SCL_LCNT);
>  	dev_dbg(dev->dev, "Fast-mode HCNT:LCNT = %d:%d\n", hcnt, lcnt);
>  
> +	/* Configure SDA Hold Time if required */
> +	if (dev->sda_hold_time)
> +		dw_writel(dev, dev->sda_hold_time, DW_IC_SDA_HOLD);
> +
>  	/* Configure Tx/Rx FIFO threshold levels */
>  	dw_writel(dev, dev->tx_fifo_depth - 1, DW_IC_TX_TL);
>  	dw_writel(dev, 0, DW_IC_RX_TL);
> diff --git a/drivers/i2c/busses/i2c-designware-core.h b/drivers/i2c/busses/i2c-designware-core.h
> index 9c1840e..33dfec3 100644
> --- a/drivers/i2c/busses/i2c-designware-core.h
> +++ b/drivers/i2c/busses/i2c-designware-core.h
> @@ -88,6 +88,7 @@ struct dw_i2c_dev {
>  	u32			master_cfg;
>  	unsigned int		tx_fifo_depth;
>  	unsigned int		rx_fifo_depth;
> +	u32			sda_hold_time;
>  };
>  
>  #define ACCESS_SWAP		0x00000001
> diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c b/drivers/i2c/busses/i2c-designware-platdrv.c
> index 8ec9133..589f414 100644
> --- a/drivers/i2c/busses/i2c-designware-platdrv.c
> +++ b/drivers/i2c/busses/i2c-designware-platdrv.c
> @@ -34,6 +34,7 @@
>  #include <linux/sched.h>
>  #include <linux/err.h>
>  #include <linux/interrupt.h>
> +#include <linux/of.h>
>  #include <linux/of_i2c.h>
>  #include <linux/platform_device.h>
>  #include <linux/pm.h>
> @@ -120,6 +121,14 @@ static int dw_i2c_probe(struct platform_device *pdev)
>  		return PTR_ERR(dev->clk);
>  	clk_prepare_enable(dev->clk);
>  
> +	if (pdev->dev.of_node) {
> +		u32 ht;
> +		u32 ic_clk = dev->get_clk_rate_khz(dev);
> +
> +		of_property_read_u32(pdev->dev.of_node, "sda-hold-time", &ht);
> +		dev->sda_hold_time = ((u64)ic_clk * ht + 500000) / 1000000;
> +	}
> +
>  	dev->functionality =
>  		I2C_FUNC_I2C |
>  		I2C_FUNC_10BIT_ADDR |
> 

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