Re: [Patch] mpc5200b: improve baud rate calculation (reach high baud rates, better accuracy)

["Albrecht Dreß" <albrecht.dress@arcor.de>]

Hi Wolfram:

[snip]
> > Yes, but I do all /calculations/ with the /4 prescaler for higher
> accuracy.
> > If the divisor exceeds the available 16 bits of the counter reg, I roun=
d
> > (divisor / 8) to use the /32 prescaler.  Think of a 19-bit counter valu=
e,
> > where I can choose to use either the lower or the higher 16 bits for th=
e
> > counter reg.
>=20
> Okay, now I got it. (Maybe this is an indication for another comment abov=
e
> the
> set divisor function?)

O.k., I will add that comment...

> > Remember also that using the higher 16 bits (/32 prescaler) is
> > probably the exceptional case - with an IPB frequency of 132 MHz this
> will
> > happen only for standard baud rates B300 and slower.
>=20
> Even the rare cases have to be correct ;)

I agree - will make the debug output and comments clearer...

[snip]
> > > This should be handled using a new compatible-entry
> > > "fsl,mpc5200b-psc-uart".
> >=20
>=20
> > I agree that this would be a lot cleaner, but it's also a lot more
> intrusive.
> > CC'ing the device tree discussion list here... comments, please!!
>=20
> Why intrusive? Maybe I miss something?

Not for the source file, but for all the dts files, if they want to benefit=
 from the detection of the '5200B.  Basically, *all* files have to be check=
ed and touched if necessary.  Again, I agree that this would be the clean a=
pproach, but I wanted to avoid that effort.  Grant???

[snip]
> Leave those two function pointers empty and fill them during probe (probe
> has
> access to the compatible-property it was matched against, see its
> arguments).
> So it should be a matter of:
>=20
> if (matched_property =3D=3D 5200b)
> =09ops->func =3D this_one;
> else
> =09ops->func =3D that_one;

Umm, yes, that's true of course.  Will pick it up.

Thanks, Albrecht.

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