linux-kernel - Re: [PATCH] drm/omap: Migrate minimum FCK/PCK ratio from Kconfig to dts

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Date:   Wed, 25 Sep 2019 14:26:27 -0700
From:   "Andrew F. Davis" <afd@...com>
To:     Tomi Valkeinen <tomi.valkeinen@...com>,
        Adam Ford <aford173@...il.com>, <linux-omap@...r.kernel.org>
CC:     Mark Rutland <mark.rutland@....com>, <devicetree@...r.kernel.org>,
        David Airlie <airlied@...ux.ie>,
        <linux-kernel@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        Tony Lindgren <tony@...mide.com>,
        Rob Herring <robh+dt@...nel.org>,
        Benoît Cousson <bcousson@...libre.com>,
        <adam.ford@...icpd.com>
Subject: Re: [PATCH] drm/omap: Migrate minimum FCK/PCK ratio from Kconfig to
 dts

On 5/28/19 4:11 AM, Tomi Valkeinen wrote:
> Hi,
> 
> On 10/05/2019 22:42, Adam Ford wrote:
>> Currently the source code is compiled using hard-coded values
>> from CONFIG_OMAP2_DSS_MIN_FCK_PER_PCK.  This patch allows this
>> clock divider value to be moved to the device tree and be changed
>> without having to recompile the kernel.
>>
>> Signed-off-by: Adam Ford <aford173@...il.com>
> 
> I understand why you want to do this, but I'm not sure it's a good idea.
> It's really something the driver should figure out, and if we add it to
> the DT, it effectively becomes an ABI.
> 
> That said... I'm not sure how good of a job the driver could ever do, as
> it can't know the future scaling needs of the userspace at the time it
> is configuring the clock. And so, I'm not nacking this patch, but I
> don't feel very good about this patch...
> 
> The setting also affects all outputs (exluding venc), which may not be
> what the user wants. Then again, I think this setting is really only
> needed on OMAP2 & 3, which have only a single output. But that's the
> same with the current kconfig option, of course.
> 
> So, the current CONFIG_OMAP2_DSS_MIN_FCK_PER_PCK is an ugly hack, in my
> opinion, and moving it to DT makes it a worse hack =). But I don't have
> any good suggestions either.
> 


Module param?

Andrew


>  Tomi
>