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Subject: Re: [RFC v2 3/5] clk: bcm2835: use firmware interface to update pllb
From:   Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
To:     Stefan Wahren <stefan.wahren@i2se.com>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Ray Jui <rjui@broadcom.com>,
        Scott Branden <sbranden@broadcom.com>,
        bcm-kernel-feedback-list@broadcom.com,
        Eric Anholt <eric@anholt.net>
Cc:     linux-pm@vger.kernel.org, sboyd@kernel.org,
        viresh.kumar@linaro.org, mturquette@baylibre.com,
        ptesarik@suse.com, rjw@rjwysocki.net, linux-kernel@vger.kernel.org,
        mbrugger@suse.de, linux-rpi-kernel@lists.infradead.org,
        linux-clk@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        ssuloev@orpaltech.com
Date:   Tue, 21 May 2019 17:47:03 +0200
In-Reply-To: <6383b357-3f7e-f031-f59f-61c598e44763@i2se.com>
References: <20190520104708.11980-1-nsaenzjulienne@suse.de>
         <20190520104708.11980-4-nsaenzjulienne@suse.de>
         <ebc78880-418f-f507-021c-41295113e041@i2se.com>
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Hi Stefan, thanks for your comments!

On Tue, 2019-05-21 at 14:40 +0200, Stefan Wahren wrote:
> Hi Nicolas,
>=20
> On 20.05.19 14:11, Stefan Wahren wrote:
> > Hi Nicolas,
> >=20
> > the following comments applies only in case Eric is fine with the whole
> > approach.
> >=20
> > On 20.05.19 12:47, Nicolas Saenz Julienne wrote:
> > > Raspberry Pi's firmware, which runs in a dedicated processor, keeps
> > maybe we should clarify that the firmware is running in the VPU
> > > track of the board's temperature and voltage. It's resposible for
> > > scaling the CPU frequency whenever it deems the device reached an uns=
afe
> > > state. On top of that the firmware provides an interface which allows
> > > Linux to to query the clock's state or change it's frequency.
> > I think this requires a separate update of the devicetree binding.
> > > Being the sole user of the bcm2835 clock driver, this integrates the
> > > firmware interface into the clock driver and adds a first user: the C=
PU
> > > pll, also known as 'pllb'.
> > Please verify that the kernel still works (and this clock driver probe)
> > under the following conditions:
> >=20
> > - CONFIG_RASPBERRYPI_FIRMWARE=3Dn
> > - CONFIG_RASPBERRYPI_FIRMWARE=3Dm
> > - older DTBs without patch #1
> i thought about this and the case this driver would return
> -EPROBE_DEFER. The clock driver is too essential for doing such a thing.
> So i think the best solution would be to move these changes into a
> separate driver which should be register by the clock driver (similiar
> to vchiq). This also avoid the need of a new device tree binding.

I understand your concerns.

Wouldn't you prefer registering the device trough the device tree? I'd go w=
ith
the same approach as the firmware touchscreen driver, which is registered a=
fter
the firmware's probe trough dt's 'simple-bus'. That said, it's not a strong=
ly
held opinion, I'm happy with whatever solution as long as it works.

I get from your comments that you'd like the register based version of 'pll=
b'
and 'pllb_arm' to be loaded if for some reason the firmware isn't available=
. Is
that right? The main problem I see with this is the duplication of 'pllb' a=
nd
'pllb_arm'. Both drivers will create the same clock device through differen=
t
interfaces. Any suggestions on how to deal with that? If not I can simply
remove 'pllb' and 'pllb_arm' from clk-bcm2835.c.

Regards,
Nicolas


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