linux-kernel - Re: [PATCH 0/3] refactor some ldb related clocks

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Message-ID: <52134030.4030502@freescale.com>
Date:	Tue, 20 Aug 2013 18:08:48 +0800
From:	Liu Ying <Ying.Liu@...escale.com>
To:	Philipp Zabel <p.zabel@...gutronix.de>
CC:	<kernel@...gutronix.de>, <gregkh@...uxfoundation.org>,
	<shawn.guo@...aro.org>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH 0/3] refactor some ldb related clocks

On 08/20/2013 05:43 PM, Philipp Zabel wrote:
> Am Dienstag, den 20.08.2013, 16:38 +0800 schrieb Liu Ying:
>> The ldb_di[0/1]_ipu_div clock dividers in the CSCMR2 register
>> of i.MX53, i.MX6Q and i.MX6DL SoCs can be configured to a 1/3.5
>> drivider or a 1/7 divider. The common clock framework cannot
>> deal with the two dividers directly even with the divider table
>> which only supports integral dividers. So, the idea is to take
>> the 1/3.5 and 1/7 dividers as separate fixed factor dividers and
>> introduce a new multiplexer clock to be derived from the them.
>> Then, the ldb display clock trees can be setup correctly.
>> This series contains the necessary clock driver changes, dts code
>> changes and imx-drm/ldb driver changes to fullfill the task.
> 
> I don't see how this improves the situation. Does this solve any real
> problem?
>

I don't see any functional problem without this series.
But, it may correct ldb_di[n] clock frequency returned from clk_get_rate() when using 1/7 divider.
Furthermore, since this series makes the ldb related clocks from pll to ldb_di[0/1] have the CLK_SET_RATE_PARENT flag set, the imx-drm/ldb driver may set the clocks' frequency more flexibly, i.e.,
only calling clk_set_rate() for ldb_di[n] clock would be an alternative.

> While I admit to having introduced the combination of 1/3.5 fixed
> divider and configurable 1/1,1/2 divder clocks to describe this
> fractional divider for the reasons you state, I think the correct
> solution would be to improve the table divider to support fractional
> values and get rid of the virtual ldb_di<n>_div_3_5 clocks, not
> introduce more virtual clocks.

Yes, it's good to support fractional values for the table divider(not sure if there is any plan for this).
I see there is something similar in 'include/linux/sh_clk.h'.

> 
> regards
> Philipp
> 
> 

Regards,
Liu Ying

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