[PATCH V3] Set sda-hold-time based on ACPI *CNT value

[PATCH V3] Set sda-hold-time based on ACPI *CNT value

[Tan Chin Yew]

For I2c to operate correctly under all speed mode, sda-hold-time need to
be perfectly tuned. However, sda-hold-time is precalculated according to
circuit parameter which make it platform-specific.

In order to get accurate sda-hold-time for all platforms, pretuned
sda-hold-time for particular platform is stored in ACPI table and driver
to load the sda holding time from ACPI table.

This patch read the I2c sda-hold-time from ACPI table and assigned the
suitable hold time based on the i2c clock frequency.

Tested on Intel Apollo Lake.

Changes in V3:
	- Remove null handling in function dw_i2c_acpi_params.
	- Add descriptions to commit message.

Changes in V2:
	- The code is realigned according to suggestion.
	- "case 400000:" is added on top of "default:" for readability.

Tan Chin Yew (1):
  i2c: designware: Get selected speed mode sda-hold-time via ACPI

 drivers/i2c/busses/i2c-designware-platdrv.c | 31 ++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

-- 
1.9.1

[PATCH] i2c: designware: Get selected speed mode sda-hold-time via ACPI

[Tan Chin Yew]

Sda-hold-time is an important parameter for tuning i2c to meet the
electrical specification especially for high speed. I2C with incorrect
sda-hold-time may cause lost arbitration error. Instead of loading all
speed mode settings, only selected speed mode settings are loaded.

Signed-off-by: Tan Chin Yew <chin.yew.tan@intel.com>
---
 drivers/i2c/busses/i2c-designware-platdrv.c | 31 ++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c b/drivers/i2c/busses/i2c-designware-platdrv.c
index a597ba32..5a4eb6b 100644
--- a/drivers/i2c/busses/i2c-designware-platdrv.c
+++ b/drivers/i2c/busses/i2c-designware-platdrv.c
@@ -85,8 +85,7 @@ static void dw_i2c_acpi_params(struct platform_device *pdev, char method[],
 
 		*hcnt = (u16)objs[0].integer.value;
 		*lcnt = (u16)objs[1].integer.value;
-		if (sda_hold)
-			*sda_hold = (u32)objs[2].integer.value;
+		*sda_hold = (u32)objs[2].integer.value;
 	}
 
 	kfree(buf.pointer);
@@ -105,14 +104,28 @@ static int dw_i2c_acpi_configure(struct platform_device *pdev)
 	dev->rx_fifo_depth = 32;
 
 	/*
-	 * Try to get SDA hold time and *CNT values from an ACPI method if
-	 * it exists for both supported speed modes.
+	 * Try to get SDA hold time and *CNT values from an ACPI method for
+	 * selected speed modes.
 	 */
-	dw_i2c_acpi_params(pdev, "SSCN", &dev->ss_hcnt, &dev->ss_lcnt, NULL);
-	dw_i2c_acpi_params(pdev, "FMCN", &dev->fs_hcnt, &dev->fs_lcnt,
-			   &dev->sda_hold_time);
-	dw_i2c_acpi_params(pdev, "FPCN", &dev->fp_hcnt, &dev->fp_lcnt, NULL);
-	dw_i2c_acpi_params(pdev, "HSCN", &dev->hs_hcnt, &dev->hs_lcnt, NULL);
+	switch (dev->clk_freq) {
+	case 100000:
+		dw_i2c_acpi_params(pdev, "SSCN", &dev->ss_hcnt, &dev->ss_lcnt,
+				   &dev->sda_hold_time);
+		break;
+	case 1000000:
+		dw_i2c_acpi_params(pdev, "FPCN", &dev->fp_hcnt, &dev->fp_lcnt,
+				   &dev->sda_hold_time);
+		break;
+	case 3400000:
+		dw_i2c_acpi_params(pdev, "HSCN", &dev->hs_hcnt, &dev->hs_lcnt,
+				   &dev->sda_hold_time);
+		break;
+	case 400000:
+	default:
+		dw_i2c_acpi_params(pdev, "FMCN", &dev->fs_hcnt, &dev->fs_lcnt,
+				   &dev->sda_hold_time);
+		break;
+	}
 
 	id = acpi_match_device(pdev->dev.driver->acpi_match_table, &pdev->dev);
 	if (id && id->driver_data)
-- 
1.9.1

Re: [PATCH] i2c: designware: Get selected speed mode sda-hold-time via ACPI

[Andy Shevchenko]

On Tue, 2017-03-28 at 16:48 +0800, Tan Chin Yew wrote:
> Sda-hold-time is an important parameter for tuning i2c to meet the
> electrical specification especially for high speed. I2C with incorrect
> sda-hold-time may cause lost arbitration error. Instead of loading all
> speed mode settings, only selected speed mode settings are loaded.
> 
> Signed-off-by: Tan Chin Yew <chin.yew.tan@intel.com>


Looks good to me:

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

> ---
>  drivers/i2c/busses/i2c-designware-platdrv.c | 31
> ++++++++++++++++++++---------
>  1 file changed, 22 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c
> b/drivers/i2c/busses/i2c-designware-platdrv.c
> index a597ba32..5a4eb6b 100644
> --- a/drivers/i2c/busses/i2c-designware-platdrv.c
> +++ b/drivers/i2c/busses/i2c-designware-platdrv.c
> @@ -85,8 +85,7 @@ static void dw_i2c_acpi_params(struct
> platform_device *pdev, char method[],
>  
>  		*hcnt = (u16)objs[0].integer.value;
>  		*lcnt = (u16)objs[1].integer.value;
> -		if (sda_hold)
> -			*sda_hold = (u32)objs[2].integer.value;
> +		*sda_hold = (u32)objs[2].integer.value;
>  	}
>  
>  	kfree(buf.pointer);
> @@ -105,14 +104,28 @@ static int dw_i2c_acpi_configure(struct
> platform_device *pdev)
>  	dev->rx_fifo_depth = 32;
>  
>  	/*
> -	 * Try to get SDA hold time and *CNT values from an ACPI
> method if
> -	 * it exists for both supported speed modes.
> +	 * Try to get SDA hold time and *CNT values from an ACPI
> method for
> +	 * selected speed modes.
>  	 */
> -	dw_i2c_acpi_params(pdev, "SSCN", &dev->ss_hcnt, &dev-
> >ss_lcnt, NULL);
> -	dw_i2c_acpi_params(pdev, "FMCN", &dev->fs_hcnt, &dev-
> >fs_lcnt,
> -			   &dev->sda_hold_time);
> -	dw_i2c_acpi_params(pdev, "FPCN", &dev->fp_hcnt, &dev-
> >fp_lcnt, NULL);
> -	dw_i2c_acpi_params(pdev, "HSCN", &dev->hs_hcnt, &dev-
> >hs_lcnt, NULL);
> +	switch (dev->clk_freq) {
> +	case 100000:
> +		dw_i2c_acpi_params(pdev, "SSCN", &dev->ss_hcnt, &dev-
> >ss_lcnt,
> +				   &dev->sda_hold_time);
> +		break;
> +	case 1000000:
> +		dw_i2c_acpi_params(pdev, "FPCN", &dev->fp_hcnt, &dev-
> >fp_lcnt,
> +				   &dev->sda_hold_time);
> +		break;
> +	case 3400000:
> +		dw_i2c_acpi_params(pdev, "HSCN", &dev->hs_hcnt, &dev-
> >hs_lcnt,
> +				   &dev->sda_hold_time);
> +		break;
> +	case 400000:
> +	default:
> +		dw_i2c_acpi_params(pdev, "FMCN", &dev->fs_hcnt, &dev-
> >fs_lcnt,
> +				   &dev->sda_hold_time);
> +		break;
> +	}
>  
>  	id = acpi_match_device(pdev->dev.driver->acpi_match_table,
> &pdev->dev);
>  	if (id && id->driver_data)

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

Re: [PATCH] i2c: designware: Get selected speed mode sda-hold-time via ACPI

[Jarkko Nikula]

On 03/28/2017 12:13 PM, Andy Shevchenko wrote:
> On Tue, 2017-03-28 at 16:48 +0800, Tan Chin Yew wrote:
>> Sda-hold-time is an important parameter for tuning i2c to meet the
>> electrical specification especially for high speed. I2C with incorrect
>> sda-hold-time may cause lost arbitration error. Instead of loading all
>> speed mode settings, only selected speed mode settings are loaded.
>>
>> Signed-off-by: Tan Chin Yew <chin.yew.tan@intel.com>
>
>
> Looks good to me:
>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
>
Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>

Re: [PATCH] i2c: designware: Get selected speed mode sda-hold-time via ACPI

[Wolfram Sang]

[-- Attachment #1: Type: text/plain, Size: 445 bytes --]

On Tue, Mar 28, 2017 at 04:48:02PM +0800, Tan Chin Yew wrote:
> Sda-hold-time is an important parameter for tuning i2c to meet the
> electrical specification especially for high speed. I2C with incorrect
> sda-hold-time may cause lost arbitration error. Instead of loading all
> speed mode settings, only selected speed mode settings are loaded.
> 
> Signed-off-by: Tan Chin Yew <chin.yew.tan@intel.com>

Applied to for-next, thanks!


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