On 07/21/2015 03:37 PM, Doug Anderson wrote:
> Stephen,
>
> On Tue, Jul 21, 2015 at 2:16 PM, Stephen Boyd <sboyd at codeaurora.org> wrote:
>> On 07/21/2015 01:41 PM, Douglas Anderson wrote:
>>> In the TRM we see that BWADJ is "a 12-bit bus that selects the values
>>> 1-4096 for the bandwidth divider (NB)":
>>> NB = BWADJ[11:0] + 1
>>> The recommended setting of NB: NB = NF / 2.
>>>
>>> So:
>>> NB = NF / 2
>>> BWADJ[11:0] + 1 = NF / 2
>>> BWADJ[11:0] = NF / 2 - 1
>>>
>>> Right now, we have:
>>>
>>> { \
>>> .rate = _rate##U, \
>>> .nr = _nr, \
>>> .nf = _nf, \
>>> .no = _no, \
>>> .bwadj = (_nf >> 1), \
>>> }
>>>
>>> That means we set bwadj to NF / 2, not NF / 2 - 1
>>>
>>> All of this is a bit confusing because we specify "NR" (the 1-based
>>> value), "NF" (the 1-based value), "NO" (the 1-based value), but
>>> "BWADJ" (the 0-based value) instead of "NB" (the 1-based value).
>>>
>>> Let's change to working with "NB" and fix the off by one error. This
>>> may affect PLL jitter in a small way (hopefully for the better).
>>>
>>> Signed-off-by: Douglas Anderson <dianders at chromium.org>
>>>
>> There's no Fixes tag or stable Cc so I take it this isn't fixing any
>> manifesting regression, more of a visual inspection bug find?
> There is no known problem fixed. I've been looking at HDMI and
> controlling PLL jitter is an important part of supporting HDMI clock
> rates. That got me to looking at this parameter and deciding that we
> should set it correctly. Apparently it doesn't help in any hugely
> significant way... I just got done re-testing a whole lot of rates
> and if it helped or hurt my jitter it's in the noise (AKA there's
> enough variance run-to-run that it's hard to tell if this made any
> difference).
>
>
Ok. Applied to clk-next.
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