Re: [PATCH 0/4] OMAP4: DSS2: Adding fclk support for DPI interface

Raghuveer Murthy
2011-02-18T15:40:01Z

On Friday 18 February 2011 12:46 AM, Valkeinen, Tomi wrote:
> On Thu, 2011-02-17 at 08:49 -0600, Paul Walmsley wrote:
>> On Wed, 16 Feb 2011, Raghuveer Murthy wrote:
>>
>
> <snip>
>
>>>
>>> DPLL_PER post divider output for DSS core functional clock can be changed in
>>> OMAP3xxx and OMAP4430, based on the requested pixel clock for a given display
>>> resolution.
>>>
>>> Additionally, the number of dividers available for DPLL_PER post dividors for
>>> DSS has increased from 16 to 32, from OMAP3630 onwards.
>>>
>>> Both these are added as dss_features.
>>>
>>> Given the above comments from Tomi, can the same be included as part of the
>>> clock framework?
>>
>> Have you considered just calling clk_round_rate() on the DPLL_PER's output
>> divider and seeing if you can get a rate that you're happy with?
>
> Hmm, yes, perhaps that would be possible.
>
> Currently we iterate suitable clocks by going through all fck dividers,
> then lck dividers and then pck dividers, and checking if one of the
> resulting pixel clocks is close to the required one.
>
> But we could start with the required pck, and go "up" from there with
> pck dividers, lck dividers, and in the end using clk_round_rate() to see
> if the set of dividers is possible.
>
> And we know the maximum allowed fck rate, so we can use that as a
> ceiling and forget any divider sets that lead to too high clocks.
>
> This will probably need a bit more iterations, though, as we may be
> trying multiple divider sets leading to the same fck rate, because the
> code doesn't have any idea what the possible rates are.
>
> I trust clk_round_rate() is quite simple function (ie. fast)?
>
> Tomi
>
>
I will look into this and come with a solution.

Regards,
Raghuveer