[RFC] serial: mxc: get the clock frequency from the used clock for the device

[Heiko Thiery]

Hi Angus,

[snip]

> > So I'm not sure if the ipg clock is the right one for the boards that
> > has different clock for ipg and per.
>
> So I only looked at imx6qdl.dtsi where the clocks are different
>
> clocks = <&clks IMX6QDL_CLK_UART_IPG>,
>           <&clks IMX6QDL_CLK_UART_SERIAL>;
> clock-names = "ipg", "per";
>
> And from that file it looks like the per clock would be the correct one.

Yes, 'per' seems to be the right one.

> Should the clock be looked up by id instead of by name and then have a
> different code path for each imx board type ?

But how to get the right clk id? The id's for all the implementations
are different. Or not?

>
> >
> >> > +     }
> >> > +
> >> > +     /* as fallback we try to get the clk rate that way */
> >> > +     if (rate == 0)
> >> > +             rate = imx_get_uartclk();
> >>
> >> Would it be better to re-write imx_get_uartclk so that both the
> >> getting
> >> and setting of clocks was correct ?
> >
> > I do not understand what you mean with that.
> >
>
> There are other places in the code that imx_get_uartclk gets called. If
> an index was added to imx_get_uartclk(int index) then you wouldn't need
> the code above in the mxc_serial_setbrg function. That would also make
> all of the places where imx_get_uartclk gets called return the correct
> value.

By index do you mean the clk id?

>
> It might make sense to create a new function imx7_get_uartclk that gets
> called on newer SOCs so that the imx6 and earlier code doesn't need to
> get changed.

At what point should this be called instead of the imx_get_uartclk() function?


>
> >> With DM clocks enabled I don't even think it makes sense to call those
> >> older functions.
> >
> > You mean when DM clocks are available the "new" method should be used
> > and no fallback to the old mechanism?
> >
>
> For older boards it makes sense to fallback to the single clock. On
> newer boards if it returned an error instead it would have been easier
> for you to figure out where the serial console failed.

--
Heiko