Re: [PATCH v1 2/7] clk: bcm: rpi: Add a function to retrieve the maximum

From: Stefan Wahren <stefan.wahren@i2se.com>
To: Stephen Boyd <sboyd@kernel.org>,
	Broadcom internal kernel review list 
	<bcm-kernel-feedback-list@broadcom.com>,
	Daniel Vetter <daniel@ffwll.ch>, David Airlie <airlied@linux.ie>,
	Emma Anholt <emma@anholt.net>,
	Florian Fainelli <f.fainelli@gmail.com>,
	Maxime Ripard <maxime@cerno.tech>,
	Maxime Ripard <mripard@kernel.org>,
	Michael Turquette <mturquette@baylibre.com>,
	Ray Jui <rjui@broadcom.com>,
	Scott Branden <sbranden@broadcom.com>
Cc: linux-arm-kernel@lists.infradead.org,
	linux-rpi-kernel@lists.infradead.org,
	dri-devel@lists.freedesktop.org,
	Dom Cobley <popcornmix@gmail.com>,
	linux-clk@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 2/7] clk: bcm: rpi: Add a function to retrieve the maximum
Date: Thu, 15 Sep 2022 08:15:48 +0200	[thread overview]
Message-ID: <5b64f4ef-a62e-80df-80a6-3ab52589588b@i2se.com> (raw)
In-Reply-To: <20220914182101.92286C433D6@smtp.kernel.org>

Hi Stephen,

Am 14.09.22 um 20:20 schrieb Stephen Boyd:
> Quoting Stefan Wahren (2022-09-14 11:09:04)
>> Am 14.09.22 um 20:05 schrieb Stephen Boyd:
>>> Quoting Stefan Wahren (2022-09-14 10:45:48)
>>>> Am 14.09.22 um 17:50 schrieb Stephen Boyd:
>>>>> Furthermore, I wonder if even that part needs to be implemented.  Why
>>>>> not make a direct call to rpi_firmware_property() and get the max rate?
>>>>> All of that can live in the drm driver. Making it a generic API that
>>>>> takes a 'struct clk' means that it looks like any clk can be passed,
>>>>> when that isn't true. It would be better to restrict it to the one use
>>>>> case so that the scope of the problem doesn't grow. I understand that it
>>>>> duplicates a few lines of code, but that looks like a fair tradeoff vs.
>>>>> exposing an API that can be used for other clks in the future.
>>>> it would be nice to keep all the Rpi specific stuff out of the DRM
>>>> driver, since there more users of it.
>>> Instead of 'all' did you mean 'any'?
>> yes
> Another idea is to populate an OPP table in the rpi firmware driver for
> this platform device with the adjusted max frequency. That would be an
> SoC/firmware agnostic interface that expresses the constraints.
Do you mean in the source code of this driver or in the DT?
> I'm
> almost certain we talked about this before.
I'm not sure about the context. Do you mean the CPU frequency handling? 
I remember it was a hard decision. In the end it was little benefit but 
a lot of disadvantages (hard to maintain all theses OPP tables for all 
Raspberry Pi boards, doesn't work with already deployed DT). So yes, i'm 
part of the problem i mentioned before ;-)