From: tomi.valkeinen@ti•com (Tomi Valkeinen)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 2/2] ARM: OMAP2+: fix dpll round_rate() to actually round
Date: Wed, 26 Feb 2014 13:48:20 +0200 [thread overview]
Message-ID: <530DD484.5040703@ti.com> (raw)
In-Reply-To: <alpine.DEB.2.02.1402201927280.10791@utopia.booyaka.com>
On 20/02/14 21:30, Paul Walmsley wrote:
> On Wed, 19 Feb 2014, Paul Walmsley wrote:
>
>> On Fri, 17 Jan 2014, Tomi Valkeinen wrote:
>>
>>> This patch adds a simple method of rounding: during the iteration, the
>>> code keeps track of the closest rate match. If no exact match is found,
>>> the closest is returned.
>>
>> So that's one possible rounding policy; maybe it works fine for a display
>> interface PLL, at least for some values of "closest rate". But another
>> might be "only allow a selection from a set of pre-determined rates
>> characterized by the silicon validation team". Or another rounding
>> function might need to select a more distant rate that minimizes jitter,
>> EMI, or power consumption.
>
> Thought about this some more. Do you only need this for the DSS PLL, or
> do you need it for one of the core OMAP PLLs?
>
> If the former, then how about modifying your patch to create a separate
> round_rate function that's only used for the DSS PLL that implements the
> behavior that you want?
>
> That would eliminate any risk of impacting other users on the system. And
> would also allow this change to get into the codebase much faster, since
> there's no need for clk API changes, etc.
The DSS internal PLLs are handled by the DSS driver, which does all
kinds of iteration to find good clocks. This patch is for a dedicated
display PLL, present on, for example, BeagleBoneBlack.
If you think that's better approach, I can take a look how it can be
done (I'm not too familiar with the clock framework). Or maybe there's a
possibility to have a flag of some kind, which allows rounded values to
be returned? That sounds like an easy addition too.
Note that the same change is needed for DT and non-DT boots. Having
separate round function would mean create a new clock "driver" (i.e.
compatibility string), wouldn't it? Adding a flag sounds easier.
Tomi
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next prev parent reply other threads:[~2014-02-26 11:48 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-17 7:44 [PATCH 0/2] ARM: OMAP2+: Fix dpll rounding Tomi Valkeinen
2014-01-17 7:44 ` [PATCH 1/2] ARM: OMAP2+: fix rate prints Tomi Valkeinen
2014-02-19 19:25 ` Paul Walmsley
2014-01-17 7:44 ` [PATCH 2/2] ARM: OMAP2+: fix dpll round_rate() to actually round Tomi Valkeinen
2014-02-13 23:00 ` Tony Lindgren
2014-02-14 13:32 ` Tero Kristo
2014-02-19 19:49 ` Paul Walmsley
2014-02-20 19:30 ` Paul Walmsley
2014-02-26 11:48 ` Tomi Valkeinen [this message]
2014-03-05 13:50 ` Tomi Valkeinen
2014-04-30 15:38 ` Felipe Balbi
2014-04-30 15:40 ` Nishanth Menon
2014-02-26 11:42 ` Tomi Valkeinen
2014-04-24 18:34 ` Felipe Balbi
2014-04-24 18:29 ` Felipe Balbi
2014-04-24 18:44 ` Tony Lindgren
2014-04-29 15:51 ` Felipe Balbi
2014-04-29 16:27 ` Tomi Valkeinen
2014-05-07 22:16 ` Paul Walmsley
2014-05-12 12:11 ` Tomi Valkeinen
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