linux-kernel - Re: [PATCH v4 09/10] arm64: dts: bcm2712: Add external clock for RP1 chipset on Rpi5

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Message-ID: <9abb376c-3399-4c2c-8e7c-cea1184ea370@lunn.ch>
Date: Sun, 24 Nov 2024 20:41:25 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Andrea della Porta <andrea.porta@...e.com>
Cc: Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...nel.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczynski <kw@...ux.com>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Bartosz Golaszewski <brgl@...ev.pl>,
	Derek Kiernan <derek.kiernan@....com>,
	Dragan Cvetic <dragan.cvetic@....com>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Saravana Kannan <saravanak@...gle.com>, linux-clk@...r.kernel.org,
	devicetree@...r.kernel.org, linux-rpi-kernel@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-gpio@...r.kernel.org,
	Masahiro Yamada <masahiroy@...nel.org>,
	Stefan Wahren <wahrenst@....net>,
	Herve Codina <herve.codina@...tlin.com>,
	Luca Ceresoli <luca.ceresoli@...tlin.com>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v4 09/10] arm64: dts: bcm2712: Add external clock for RP1
 chipset on Rpi5

On Sun, Nov 24, 2024 at 11:51:46AM +0100, Andrea della Porta wrote:
> The RP1 found on Raspberry Pi 5 board needs an external crystal at 50MHz.
> Add clk_rp1_xosc node to provide that.

I'm wondering if this is the correct place for this clock. From your
description, the bcm2712 itself does not provide the clock. There is a
crystal on the board. So the board provides the clock. What happens
when the RP1 is used on other boards? Also, does the RP1 need an
actual crystal, or can you feed it a clock? Often such inputs are
flexible, you can connect a crystal across two pins, or you can feed a
clock into one pin.

If a crystal is the only choice, i would probably have it part of the
RP1 overlay. If a clock can be used, i would make it a board property.

	Andrew