[PATCH v1] i2c: designware: save the preset value of DW_IC_SDA_HOLD

[PATCH v1] i2c: designware: save the preset value of DW_IC_SDA_HOLD

[Zhuo-hao Lee]

There are several ways to set the SDA hold time for i2c controller,
including: Device Tree, built-in device properties and ACPI. However,
if the SDA hold time is not specified by above method, we should
read the value, where it is preset by firmware, and save it to
sda_hold_time. This is needed because when i2c controller enters
runtime suspend, the DW_IC_SDA_HOLD value will be reset to chipset
default value. And during runtime resume, i2c_dw_init will be called
to reconfigure i2c controller. If sda_hold_time is zero, the chipset
default hold time will be used, that will be too short for some
platforms. Therefore, to have a better tolerance, the DW_IC_SDA_HOLD
value should be kept by sda_hold_time.

Signed-off-by: Zhuo-hao Lee <zhuo-hao.lee@intel.com>
---
 drivers/i2c/busses/i2c-designware-core.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c
index c6922b8..fcd973d 100644
--- a/drivers/i2c/busses/i2c-designware-core.c
+++ b/drivers/i2c/busses/i2c-designware-core.c
@@ -367,13 +367,17 @@ int i2c_dw_init(struct dw_i2c_dev *dev)
 	dev_dbg(dev->dev, "Fast-mode HCNT:LCNT = %d:%d\n", hcnt, lcnt);
 
 	/* Configure SDA Hold Time if required */
-	if (dev->sda_hold_time) {
-		reg = dw_readl(dev, DW_IC_COMP_VERSION);
-		if (reg >= DW_IC_SDA_HOLD_MIN_VERS)
+	reg = dw_readl(dev, DW_IC_COMP_VERSION);
+	if (reg >= DW_IC_SDA_HOLD_MIN_VERS) {
+		if (dev->sda_hold_time) {
 			dw_writel(dev, dev->sda_hold_time, DW_IC_SDA_HOLD);
-		else
-			dev_warn(dev->dev,
-				"Hardware too old to adjust SDA hold time.");
+		} else {
+			/* Keep previous hold time setting if no one set it */
+			dev->sda_hold_time = dw_readl(dev, DW_IC_SDA_HOLD);
+		}
+	} else {
+		dev_warn(dev->dev,
+			"Hardware too old to adjust SDA hold time.\n");
 	}
 
 	/* Configure Tx/Rx FIFO threshold levels */
-- 
1.9.1

Re: [PATCH v1] i2c: designware: save the preset value of DW_IC_SDA_HOLD

[Andy Shevchenko]

On Sat, 2016-08-27 at 15:39 +0800, Zhuo-hao Lee wrote:
> There are several ways to set the SDA hold time for i2c controller,
> including: Device Tree, built-in device properties and ACPI. However,
> if the SDA hold time is not specified by above method, we should
> read the value, where it is preset by firmware, and save it to
> sda_hold_time. This is needed because when i2c controller enters
> runtime suspend, the DW_IC_SDA_HOLD value will be reset to chipset
> default value. And during runtime resume, i2c_dw_init will be called
> to reconfigure i2c controller. If sda_hold_time is zero, the chipset
> default hold time will be used, that will be too short for some
> platforms. Therefore, to have a better tolerance, the DW_IC_SDA_HOLD
> value should be kept by sda_hold_time.

Looks good to me.
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

> 
> Signed-off-by: Zhuo-hao Lee <zhuo-hao.lee@intel.com>
> ---
>  drivers/i2c/busses/i2c-designware-core.c | 16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-designware-core.c
> b/drivers/i2c/busses/i2c-designware-core.c
> index c6922b8..fcd973d 100644
> --- a/drivers/i2c/busses/i2c-designware-core.c
> +++ b/drivers/i2c/busses/i2c-designware-core.c
> @@ -367,13 +367,17 @@ int i2c_dw_init(struct dw_i2c_dev *dev)
>  	dev_dbg(dev->dev, "Fast-mode HCNT:LCNT = %d:%d\n", hcnt,
> lcnt);
>  
>  	/* Configure SDA Hold Time if required */
> -	if (dev->sda_hold_time) {
> -		reg = dw_readl(dev, DW_IC_COMP_VERSION);
> -		if (reg >= DW_IC_SDA_HOLD_MIN_VERS)
> +	reg = dw_readl(dev, DW_IC_COMP_VERSION);
> +	if (reg >= DW_IC_SDA_HOLD_MIN_VERS) {
> +		if (dev->sda_hold_time) {
>  			dw_writel(dev, dev->sda_hold_time,
> DW_IC_SDA_HOLD);
> -		else
> -			dev_warn(dev->dev,
> -				"Hardware too old to adjust SDA hold
> time.");
> +		} else {
> +			/* Keep previous hold time setting if no one
> set it */
> +			dev->sda_hold_time = dw_readl(dev,
> DW_IC_SDA_HOLD);
> +		}
> +	} else {
> +		dev_warn(dev->dev,
> +			"Hardware too old to adjust SDA hold
> time.\n");
>  	}
>  
>  	/* Configure Tx/Rx FIFO threshold levels */

-- 
Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Intel Finland Oy

Re: [PATCH v1] i2c: designware: save the preset value of DW_IC_SDA_HOLD

[Jarkko Nikula]

On 08/28/2016 03:31 PM, Andy Shevchenko wrote:
> On Sat, 2016-08-27 at 15:39 +0800, Zhuo-hao Lee wrote:
>> There are several ways to set the SDA hold time for i2c controller,
>> including: Device Tree, built-in device properties and ACPI. However,
>> if the SDA hold time is not specified by above method, we should
>> read the value, where it is preset by firmware, and save it to
>> sda_hold_time. This is needed because when i2c controller enters
>> runtime suspend, the DW_IC_SDA_HOLD value will be reset to chipset
>> default value. And during runtime resume, i2c_dw_init will be called
>> to reconfigure i2c controller. If sda_hold_time is zero, the chipset
>> default hold time will be used, that will be too short for some
>> platforms. Therefore, to have a better tolerance, the DW_IC_SDA_HOLD
>> value should be kept by sda_hold_time.
>
> Looks good to me.
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
>
Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>

Re: [PATCH v1] i2c: designware: save the preset value of DW_IC_SDA_HOLD

[Wolfram Sang]

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On Sat, Aug 27, 2016 at 03:39:30PM +0800, Zhuo-hao Lee wrote:
> There are several ways to set the SDA hold time for i2c controller,
> including: Device Tree, built-in device properties and ACPI. However,
> if the SDA hold time is not specified by above method, we should
> read the value, where it is preset by firmware, and save it to
> sda_hold_time. This is needed because when i2c controller enters
> runtime suspend, the DW_IC_SDA_HOLD value will be reset to chipset
> default value. And during runtime resume, i2c_dw_init will be called
> to reconfigure i2c controller. If sda_hold_time is zero, the chipset
> default hold time will be used, that will be too short for some
> platforms. Therefore, to have a better tolerance, the DW_IC_SDA_HOLD
> value should be kept by sda_hold_time.
> 
> Signed-off-by: Zhuo-hao Lee <zhuo-hao.lee@intel.com>

Looks good. But is it a bugfix? Looks more like for-next material to me,
but not sure...


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RE: [PATCH v1] i2c: designware: save the preset value of DW_IC_SDA_HOLD

[Lee, Zhuo-hao]

>On Sat, Aug 27, 2016 at 03:39:30PM +0800, Zhuo-hao Lee wrote:
>> There are several ways to set the SDA hold time for i2c controller,
>> including: Device Tree, built-in device properties and ACPI. However, 
>> if the SDA hold time is not specified by above method, we should read 
>> the value, where it is preset by firmware, and save it to 
>> sda_hold_time. This is needed because when i2c controller enters 
>> runtime suspend, the DW_IC_SDA_HOLD value will be reset to chipset 
>> default value. And during runtime resume, i2c_dw_init will be called 
>> to reconfigure i2c controller. If sda_hold_time is zero, the chipset 
>> default hold time will be used, that will be too short for some 
>> platforms. Therefore, to have a better tolerance, the DW_IC_SDA_HOLD 
>> value should be kept by sda_hold_time.
>> 
>> Signed-off-by: Zhuo-hao Lee <zhuo-hao.lee@intel.com>

>Looks good. But is it a bugfix? Looks more like for-next material to me, but not sure...
Yes, as least for me, this is a bug.
This is an error handling in case Device Tree, built-in device properties and ACPI were not set 
the SDA hold time. We should use the firmware setting instead of chipset reset value. 

Re: [PATCH v1] i2c: designware: save the preset value of DW_IC_SDA_HOLD

[Wolfram Sang]

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On Sat, Aug 27, 2016 at 03:39:30PM +0800, Zhuo-hao Lee wrote:
> There are several ways to set the SDA hold time for i2c controller,
> including: Device Tree, built-in device properties and ACPI. However,
> if the SDA hold time is not specified by above method, we should
> read the value, where it is preset by firmware, and save it to
> sda_hold_time. This is needed because when i2c controller enters
> runtime suspend, the DW_IC_SDA_HOLD value will be reset to chipset
> default value. And during runtime resume, i2c_dw_init will be called
> to reconfigure i2c controller. If sda_hold_time is zero, the chipset
> default hold time will be used, that will be too short for some
> platforms. Therefore, to have a better tolerance, the DW_IC_SDA_HOLD
> value should be kept by sda_hold_time.
> 
> Signed-off-by: Zhuo-hao Lee <zhuo-hao.lee@intel.com>

Applied to for-current, thanks!


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