> On Tue, Oct 01, 2024 at 04:29:33PM +0800, Michael Wu wrote: > > Since there are no registers controlling the hardware parameters > > IC_CAP_LOADING and IC_CLK_FREQ_OPTIMIZATION, their values can only be > > declared in the device tree. > > > > snps,bus-capacitance-pf indicates the bus capacitance in picofarads (pF). > > It affects the high and low pulse width of SCL line in high speed mode. > > The legal values for this property are 100 and 400 only, and default > > value is 100. This property corresponds to IC_CAP_LOADING. > > > > snps,clk-freq-optimized indicates whether the hardware input clock > > frequency is reduced by reducing the internal latency. This property > > corresponds to IC_CLK_FREQ_OPTIMIZATION. > > > > The driver can calculate hs_hcnt and hs_lcnt appropriate for the hardware > > based on these two properties. > > > > Signed-off-by: Michael Wu <michael.wu@xxxxxxxxx> > > --- > > .../bindings/i2c/snps,designware-i2c.yaml | 24 > +++++++++++++++++++ > > 1 file changed, 24 insertions(+) > > > > diff --git > a/Documentation/devicetree/bindings/i2c/snps,designware-i2c.yaml > b/Documentation/devicetree/bindings/i2c/snps,designware-i2c.yaml > > index 60035a787e5c..c373f3acd34b 100644 > > --- a/Documentation/devicetree/bindings/i2c/snps,designware-i2c.yaml > > +++ b/Documentation/devicetree/bindings/i2c/snps,designware-i2c.yaml ... > > + This property indicates the bus capacitance in picofarads (pF). > > + This value is used to compute the tHIGH and tLOW periods for high > speed > > + mode. > > + default: 100 > > I asked for some constraints here. min/maximum. I think you never > replied to this. > In I2C DesignWare Databook v2.03a the mandatory option is provided to select whether the bus capacitance is 400pF or 100pF. It presents the description like that: Description: For high speed mode, the bus loading (pF) affects the high and low pulse width of SCL. Values: 100, 400 Default Value: 100 Parameter Name: IC_CAP_LOADING There is no further information describing this option except to the declaration of legal values above, let alone minimum and maximum limits. As a user I don't think I have the right to define a value range for the vendor.