linux-kernel - Re: [PATCH v5 80/80] ARM: dts: bcm2711: Enable the display pipeline

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Date:   Thu, 01 Oct 2020 18:47:13 +0200
From:   Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
To:     Tim Gover <tim.gover@...pberrypi.com>,
        Maxime Ripard <maxime@...no.tech>
Cc:     Stefan Wahren <stefan.wahren@...e.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Eric Anholt <eric@...olt.net>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Hoegeun Kwon <hoegeun.kwon@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        bcm-kernel-feedback-list@...adcom.com,
        linux-rpi-kernel@...ts.infradead.org,
        Phil Elwell <phil@...pberrypi.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5 80/80] ARM: dts: bcm2711: Enable the display pipeline

Hi Tim, thanks for the info!

On Thu, 2020-10-01 at 11:15 +0100, Tim Gover wrote:
> hdmi_enable_4k60=1 causes the firmware to select 3.3 GHz for the PLLC
> VCO to support a core-frequency of 550 MHz which is the minimum
> frequency required by the HVS at 4Kp60. The side effect is that if the
> display clock requirements are lower than 4Kp60 then you will see
> different core frequencies selected by DVFS.
> 
> If enable_uart=1 and the mini-uart is selected (default unless

What is the actual test made to check if mini-uart is selected? I can't get
firmware to trigger this behaviour with 64-bit upstream kernel/dts. Note that I
see the core clk setup at 200MHz just before having VC4 set it to 500MHz.

The only thing I've got on my config.txt is:

enable_uart=1
arm_64bit=1

Maybe we're missing some kind of DT alias upstream?

Regards,
Nicolas

> bluetooth is disabled) then the firmware will pin the core-frequency
> to either core_freq max (500 or 550). Although, I think there is a way
> of pinning it to a lower fixed frequency.
> 
> The table in overclocking.md defines options for setting the maximum
> core frequency but unless core_freq_min is specified DVFS will
> automatically pick the lowest idle frequency required by the display
> resolution.


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