Re: [PATCH v2 2/2] i2c: dwsignware: determine HS tHIGH and tLOW based on HW parameters

[Krzysztof Kozlowski]

On Fri, Sep 27, 2024 at 12:22:17PM +0800, Michael Wu wrote:
> In commit 35eba185fd1a ("i2c: designware: Calculate SCL timing parameter
> for High Speed Mode") hs_hcnt and hs_lcnt are calculated based on fixed
> tHIGH = 160 and tLOW = 120. However, the set of these fixed values only
> applies to the combination of hardware parameters IC_CAP_LOADING = 400pF
> and IC_CLK_FREQ_OPTIMIZATION = 1. Outside of this combination, if these
> fixed tHIGH = 160 and tLOW = 120 are still used, the calculated hs_hcnt
> and hs_lcnt may not be small enough, making it impossible for the SCL
> frequency to reach 3.4 MHz.
> 
> Section 3.15.4.5 in DesignWare DW_apb_i2b Databook v2.03 says that when
> IC_CLK_FREQ_OPTIMIZATION = 0,
> 
>     MIN_SCL_HIGHtime = 60 ns for 3.4 Mbps, bus loading = 100pF
> 		     = 120 ns for 3.4 Mbps, bus loading = 400pF
>     MIN_SCL_LOWtime = 160 ns for 3.4 Mbps, bus loading = 100pF
> 		    = 320 ns for 3.4 Mbps, bus loading = 400pF
> 
> and section 3.15.4.6 says that when IC_CLK_FREQ_OPTIMIZATION = 1,
> 
>     MIN_SCL_HIGHtime = 60 ns for 3.4 Mbps, bus loading = 100pF
> 		     = 160 ns for 3.4 Mbps, bus loading = 400pF
>     MIN_SCL_LOWtime = 120 ns for 3.4 Mbps, bus loading = 100pF
> 		    = 320 ns for 3.4 Mbps, bus loading = 400pF
> 
> In order to calculate more accurate hs_hcnt amd hs_lcnt, two hardware
> parameters IC_CAP_LOADING and IC_CLK_FREQ_OPTIMIZATION must be
> considered together.
> 
> Signed-off-by: Michael Wu <michael.wu@xxxxxxxxx>
> ---
>  drivers/i2c/busses/i2c-designware-common.c | 16 ++++++++++++++++
>  drivers/i2c/busses/i2c-designware-core.h   |  6 ++++++
>  drivers/i2c/busses/i2c-designware-master.c | 14 ++++++++++++--
>  3 files changed, 34 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-designware-common.c b/drivers/i2c/busses/i2c-designware-common.c
> index 080204182bb5..907f049f09f8 100644
> --- a/drivers/i2c/busses/i2c-designware-common.c
> +++ b/drivers/i2c/busses/i2c-designware-common.c
> @@ -372,6 +372,20 @@ static void i2c_dw_adjust_bus_speed(struct dw_i2c_dev *dev)
>  		t->bus_freq_hz = I2C_MAX_FAST_MODE_FREQ;
>  }
>  
> +static void i2c_dw_fw_parse_hw_params(struct dw_i2c_dev *dev)
> +{
> +	struct device *device = dev->dev;
> +	int ret;
> +
> +	ret = device_property_read_u32(device, "bus-capacitance-pf", &dev->bus_capacitance_pf);
> +	if (ret || dev->bus_capacitance_pf < 400)

Your binding said nothing about some limits here. Something is not
complete. You might be missing constraints in the binding.


> +		dev->bus_capacitance_pf = 100;
> +	else
> +		dev->bus_capacitance_pf = 400;
> +
> +	dev->clk_freq_optimized = device_property_read_bool(device, "clk-freq-optimized");

Best regards,
Krzysztof