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.
...
> +static void i2c_dw_fw_parse_hw_params(struct dw_i2c_dev *dev)
Separate function is an overkill. Just inline its contents...
...
> + ret = device_property_read_u32(device, "bus-capacitance-pf", &dev->bus_capacitance_pf);
> + if (ret || dev->bus_capacitance_pf < 400)
> + dev->bus_capacitance_pf = 100;
> + else
> + dev->bus_capacitance_pf = 400;
> +
> + dev->clk_freq_optimized = device_property_read_bool(device, "clk-freq-optimized");
...
> i2c_parse_fw_timings(device, t, false);
>
> + i2c_dw_fw_parse_hw_params(dev);
...here.
> i2c_dw_adjust_bus_speed(dev);
...
> + * @bus_capacitance_pf: bus capacitance in picofarad
picofarads
...
> + u32 t_high, t_low;
> +
> + if (dev->bus_capacitance_pf == 400) {
> + t_high = dev->clk_freq_optimized ? 160 : 120;
> + t_low = 320;
> + } else {
Yeah, this has no protection against wrong values in the DT/ACPI.
So, perhaps
} else if (...) {
and assign defaults or bail out with an error?
> + t_high = 60;
> + t_low = dev->clk_freq_optimized ? 120 : 160;
> + }
--
With Best Regards,
Andy Shevchenko
