Re: [PATCH v2 1/2] i2c: davinci: Optimize clock generation on Keystone SoC

[Grygorii Strashko <grygorii.strashko-l0cyMroinI0@public.gmane.org>]

On 08/21/2015 12:46 PM, Alexander Sverdlin wrote:
> According to "KeyStone Architecture Inter-IC Control Bus User Guide", fixed
> additive part of frequency divisors (referred as "d" in the code and datasheet)
> always equals to 6, independent of module clock prescaler.
>
>                           module clock frequency
> master clock frequency = ----------------------
>                           (ICCL + 6) + (ICCH + 6)
>
> It was not the case with original Davinci IP. Introduce new compatible property
> "ti,keystone-i2c", which triggers special handling in the driver.
>
> Without this change Keystone-based systems (having 204.8MHz input clock) choose
> prescaler 29 (PSC=28). Using d=5 in this case leads to bus bitrate ~353kHz
> instead of requested 400kHz. After correction, assuming d=6 bus rate is ~392kHz.
> This gives ~11% transfer rate increase.

Thanks Alexander.
Reviewed-by: Grygorii Strashko <grygorii.strashko-l0cyMroinI0@public.gmane.org>

>
> Signed-off-by: Alexander Sverdlin <alexander.sverdlin-xNZwKgViW5gAvxtiuMwx3w@public.gmane.org>
> Tested-by: Hemanth Guruva Reddy <hemanth.guruva_reddy-xNZwKgViW5gAvxtiuMwx3w@public.gmane.org>
> Tested-by: Lukasz Gemborowski <lukasz.gemborowski-xNZwKgViW5gAvxtiuMwx3w@public.gmane.org>
> ---
>   .../devicetree/bindings/i2c/i2c-davinci.txt        |    6 +++---
>   drivers/i2c/busses/i2c-davinci.c                   |    8 ++++++++
>   2 files changed, 11 insertions(+), 3 deletions(-)
>
> Changes in v2:
> - Introducing new "compatible" property "ti,keystone-i2c" instead of guessing
>    silicon revision from ID registers
>
> diff --git a/Documentation/devicetree/bindings/i2c/i2c-davinci.txt b/Documentation/devicetree/bindings/i2c/i2c-davinci.txt
> index a4e1cbc..5b123e0 100644
> --- a/Documentation/devicetree/bindings/i2c/i2c-davinci.txt
> +++ b/Documentation/devicetree/bindings/i2c/i2c-davinci.txt
> @@ -1,10 +1,10 @@
> -* Texas Instruments Davinci I2C
> +* Texas Instruments Davinci/Keystone I2C
>
>   This file provides information, what the device node for the
> -davinci i2c interface contain.
> +davinci/keystone i2c interface contains.
>
>   Required properties:
> -- compatible: "ti,davinci-i2c";
> +- compatible: "ti,davinci-i2c" or "ti,keystone-i2c";
>   - reg : Offset and length of the register set for the device
>
>   Recommended properties :
> diff --git a/drivers/i2c/busses/i2c-davinci.c b/drivers/i2c/busses/i2c-davinci.c
> index 3fbb9a0..c5628a4 100644
> --- a/drivers/i2c/busses/i2c-davinci.c
> +++ b/drivers/i2c/busses/i2c-davinci.c
> @@ -181,6 +181,7 @@ static void i2c_davinci_calc_clk_dividers(struct davinci_i2c_dev *dev)
>   	u32 clkh;
>   	u32 clkl;
>   	u32 input_clock = clk_get_rate(dev->clk);
> +	struct device_node *of_node = dev->dev->of_node;
>
>   	/* NOTE: I2C Clock divider programming info
>   	 * As per I2C specs the following formulas provide prescaler
> @@ -196,6 +197,9 @@ static void i2c_davinci_calc_clk_dividers(struct davinci_i2c_dev *dev)
>   	 * where if PSC == 0, d = 7,
>   	 *       if PSC == 1, d = 6
>   	 *       if PSC > 1 , d = 5
> +	 *
> +	 * Note:
> +	 * d is always 6 on Keystone I2C controller
>   	 */
>
>   	/* get minimum of 7 MHz clock, but max of 12 MHz */
> @@ -204,6 +208,9 @@ static void i2c_davinci_calc_clk_dividers(struct davinci_i2c_dev *dev)
>   		psc++;	/* better to run under spec than over */
>   	d = (psc >= 2) ? 5 : 7 - psc;
>
> +	if (of_node && of_device_is_compatible(of_node, "ti,keystone-i2c"))
> +		d = 6;
> +
>   	clk = ((input_clock / (psc + 1)) / (pdata->bus_freq * 1000));
>   	/* Avoid driving the bus too fast because of rounding errors above */
>   	if (input_clock / (psc + 1) / clk > pdata->bus_freq * 1000)
> @@ -726,6 +733,7 @@ static struct i2c_algorithm i2c_davinci_algo = {
>
>   static const struct of_device_id davinci_i2c_of_match[] = {
>   	{.compatible = "ti,davinci-i2c", },
> +	{.compatible = "ti,keystone-i2c", },
>   	{},
>   };
>   MODULE_DEVICE_TABLE(of, davinci_i2c_of_match);
>


-- 
regards,
-grygorii