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Date:   Fri, 28 Aug 2020 11:11:19 +0200
From:   Maxime Ripard <maxime@cerno.tech>
To:     Stefan Wahren <stefan.wahren@i2se.com>
Cc:     Hoegeun Kwon <hoegeun.kwon@samsung.com>, nsaenzjulienne@suse.de,
        eric@anholt.net, devicetree@vger.kernel.org,
        tim.gover@raspberrypi.com, dave.stevenson@raspberrypi.com,
        sboyd@kernel.org, mturquette@baylibre.com, kdasu.kdev@gmail.com,
        linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
        linux-clk@vger.kernel.org, robh+dt@kernel.org,
        bcm-kernel-feedback-list@broadcom.com,
        linux-rpi-kernel@lists.infradead.org, phil@raspberrypi.com,
        linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 3/3] drm/vc4: hdmi: Add pixel bvb clock control
Message-ID: <20200828091119.2kykcxixw247kfno@gilmour.lan>
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Hi Stefan,

On Thu, Aug 27, 2020 at 11:49:34AM +0200, Stefan Wahren wrote:
> Am 27.08.20 um 06:35 schrieb Hoegeun Kwon:
> > Hi Stefan,
> >
> > Thank you for your review.
> >
> >
> > On 8/26/20 7:04 PM, Stefan Wahren wrote:
> >> Hi Hoeguen,
> >>
> >> Am 21.08.20 um 09:10 schrieb Hoegeun Kwon:
> >>> There is a problem that the output does not work at a resolution
> >>> exceeding FHD. To solve this, we need to adjust the bvb clock at a
> >>> resolution exceeding FHD.
> >> this patch introduces a mandatory clock, please update
> >> brcm,bcm2835-hdmi.yaml first.
> >>
> >> Is this clock physically available on BCM283x or only on BCM2711?
> > As far as I know, BCM2711 raspberry pi 4 supports 4k,
> >
> > don't supported on pi 3 and pi 3+.
> >
> > Since 4k is not supported in versions prior to Raspberry Pi 4,
> >
> > I don't think we need to modify the bvb clock.
> >
> >
> > So I think it is better to update 'brcm,bcm2711-hdmi.yaml'
> >
> > instead of 'brcm,bcm2835-hdmi.yaml'.
>=20
> You are correct please update only brcm,bcm2711-hdmi.yaml.
>=20
> My concern was that the function vc4_hdmi_encoder_pre_crtc_configure()
> is called on a non-bcm2711 platform or on a Raspberry Pi 4 with an older
> DTB. So making the BVB clock optional might be better?

It won't cause any issue on a non-RPi4 platform since the clock pointer
will be NULL and clk_set_rate can deal with NULL pointers just fine:
https://elixir.bootlin.com/linux/latest/source/drivers/clk/clk.c#L2221

For the older DTBs, it shouldn't be an issue either. We haven't merged
the binding yet, so we don't have an upstream DTB using it

Maxime