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

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Date:   Thu, 15 Sep 2022 08:54:59 +0100
From:   Maxime Ripard <maxime@...no.tech>
To:     Stefan Wahren <stefan.wahren@...e.com>
Cc:     Stephen Boyd <sboyd@...nel.org>,
        Broadcom internal kernel review list 
        <bcm-kernel-feedback-list@...adcom.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>, Emma Anholt <emma@...olt.net>,
        Florian Fainelli <f.fainelli@...il.com>,
        Michael Turquette <mturquette@...libre.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-rpi-kernel@...ts.infradead.org,
        dri-devel@...ts.freedesktop.org, Dom Cobley <popcornmix@...il.com>,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/7] clk: bcm: rpi: Add a function to retrieve the
 maximum

On Wed, Sep 14, 2022 at 08:26:55PM +0200, Stefan Wahren wrote:
> Am 14.09.22 um 20:14 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
> > Why?
> This firmware is written specific for the Raspberry Pi and not stable from
> interface point of view. So i'm afraid that the DRM driver is only usable
> for the Raspberry Pi at the end with all these board specific dependencies.

I'm open for suggestions there, but is there any other bcm2711 device
that we support upstream?

If not, I'm not sure what the big deal is at this point. Chances are the
DRM driver won't work as is on a different board.

Plus, such a board wouldn't be using config.txt at all, so this whole
dance to find what was enabled or not wouldn't be used at all.

> Emma invested a lot of time to make this open source and now it looks that
> like that more and more functionality moves back to firmware.

What functionality has been moved back to firmware?

Maxime

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