Re: [V5] tty: serial: qcom-geni-serial: Fix get_clk_div_rate() which otherwise could return a sub-optimal clock rate.

[Vijaya Krishna Nivarthi]

On 7/14/2022 4:16 PM, Jiri Slaby wrote:
> On 12. 07. 22, 14:45, Vijaya Krishna Nivarthi wrote:
> ...
> > +static unsigned long get_clk_div_rate(struct clk *clk, struct device 
> > *dev,
> > +        unsigned int baud, unsigned int sampling_rate, unsigned int 
> > *clk_div)
> > +{
> > +    unsigned long ser_clk;
> > +    unsigned long desired_clk;
> > +
> > +    desired_clk = baud * sampling_rate;
> > +    if (!desired_clk) {
> > +        dev_dbg(dev, "Invalid frequency\n");
> > +        return 0;
> >       }
> >   -    *clk_div = ser_clk / desired_clk;
> > -    if (!(*clk_div))
> > -        *clk_div = 1;
> > +    /*
> > +     * try to find a clock rate within 2% tolerance, then within
>
> "then within" ... "5" is missing, perhaps?


Yes :(

Will change.


> > +     */
> > +    ser_clk = find_clk_rate_in_tol(clk, desired_clk, clk_div, 2);
> > +    if (!ser_clk)
> > +        ser_clk = find_clk_rate_in_tol(clk, desired_clk, clk_div, 5);
> > +
> > +    if (!ser_clk)
> > +        dev_err(dev, "Couldn't find suitable clock rate for %lu\n", 
> > desired_clk);
> > +    else
> > +        dev_dbg(dev, "desired_clk-%lu, ser_clk-%lu, clk_div-%u\n",
> > +                desired_clk, ser_clk, *clk_div);
> >         return ser_clk;
> >   }
> > @@ -1021,8 +1040,8 @@ static void qcom_geni_serial_set_termios(struct 
> > uart_port *uport,
> >       if (ver >= QUP_SE_VERSION_2_5)
> >           sampling_rate /= 2;
> >   -    clk_rate = get_clk_div_rate(port->se.clk, baud,
> > -        sampling_rate, &clk_div);
> > +    clk_rate = get_clk_div_rate(port->se.clk, port->se.dev, baud,
>
> Maybe worth passing whole geni_se (port->se) then?


but then geni_se is a struct; shall we pass port instead?

Alternately move logging to caller?

Thank you.


> > +                    sampling_rate, &clk_div);
> >       if (!clk_rate)
> >           goto out_restart_rx;
>
> thanks,