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

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+	if (is_mpc5200b == 1)
+		return mpc5xxx_get_bus_frequency(p) * 4;
+	else
+		return mpc5xxx_get_bus_frequency(p) / 2;

Isn't this wrong? You can also have /32 on the 5200B (the fallback).

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 round
(divisor / 8) to use the /32 prescaler.  Think of a 19-bit counter value,
where I can choose to use either the lower or the higher 16 bits for the
counter reg.

Okay, now I got it. (Maybe this is an indication for another comment above the
set divisor function?)

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.

Even the rare cases have to be correct ;)

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+	/* Check only once if we are running on a mpc5200b or not */
+	if (is_mpc5200b == -1) {
+		struct device_node *np;
+
+		np = of_find_compatible_node(NULL, NULL, "fsl,mpc5200b-immr");

This should be handled using a new compatible-entry
"fsl,mpc5200b-psc-uart".

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!!

Why intrusive? Maybe I miss something?

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You could also have a set_divisor-function for 5200 and 5200B and set it
here in the function struct (one reason less for the static ;))

Hmmm, but then I would need a 'static struct psc_ops mpc5200b_psc_ops', where
only two functions differ from the generic 52xx struct as it is implemented
now.  Using the static int needs less space.  However, in combination with
the new compatible entry, it would of course make sense.

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:

if (matched_property == 5200b)
	ops->func = this_one;
else
	ops->func = that_one;

Regards,

   Wolfram

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