linux-kernel - Re: [PATCH v11 07/13] misc: rp1: RaspberryPi RP1 misc driver

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Message-ID: <aDhhXF_MNn34Bu2N@apocalypse>
Date: Thu, 29 May 2025 15:30:04 +0200
From: Andrea della Porta <andrea.porta@...e.com>
To: Matthias Brugger <mbrugger@...e.com>
Cc: Andrea della Porta <andrea.porta@...e.com>,
	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-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>,
	Andrew Lunn <andrew@...n.ch>, Phil Elwell <phil@...pberrypi.com>,
	Dave Stevenson <dave.stevenson@...pberrypi.com>,
	kernel-list@...pberrypi.com
Subject: Re: [PATCH v11 07/13] misc: rp1: RaspberryPi RP1 misc driver

Hi Matthias,

On 15:24 Thu 29 May     , Matthias Brugger wrote:
> 
> 
> On 29/05/2025 14:43, Andrea della Porta wrote:
> > The RaspberryPi RP1 is a PCI multi function device containing
> > peripherals ranging from Ethernet to USB controller, I2C, SPI
> > and others.
> > 
> > Implement a bare minimum driver to operate the RP1, leveraging
> > actual OF based driver implementations for the on-board peripherals
> > by loading a devicetree overlay during driver probe if the RP1
> > node is not already present in the DT.
> > 
> > The peripherals are accessed by mapping MMIO registers starting
> > from PCI BAR1 region.
> > 
> > With the overlay approach we can achieve more generic and agnostic
> > approach to managing this chipset, being that it is a PCI endpoint
> > and could possibly be reused in other hw implementations. The
> > presented approach is also used by Bootlin's Microchip LAN966x
> > patchset (see link) as well, for a similar chipset.
> > In this case, the inclusion tree for the DT overlay is as follow
> > (the arrow points to the includer):
> > 
> >   rp1-pci.dtso <---- rp1-common.dtsi
> > 
> > On the other hand, to ensure compatibility with downstream, this
> > driver can also work with a DT already comprising the RP1 node, so
> > the dynamically loaded overlay will not be used if the DT is already
> > fully defined.
> > 
> > The reason why this driver is contained in drivers/misc has
> > been paved by Bootlin's LAN966X driver, which first used the
> > overlay approach to implement non discoverable peripherals behind a
> > PCI bus. For RP1, the same arguments apply: it's not used as an SoC
> > since the driver code is not running on-chip and is not like an MFD
> > since it does not really need all the MFD infrastructure (shared regs,
> > etc.). So, for this particular use, misc has been proposed and deemed
> > as a good choice. For further details about that please check the links.
> > 
> > This driver is heavily based on downstream code from RaspberryPi
> > Foundation, and the original author is Phil Elwell.
> > 
> > Link: https://datasheets.raspberrypi.com/rp1/rp1-peripherals.pdf
> > Link: https://lore.kernel.org/all/20240612140208.GC1504919@google.com/
> > Link: https://lore.kernel.org/all/83f7fa09-d0e6-4f36-a27d-cee08979be2a@app.fastmail.com/
> > Link: https://lore.kernel.org/all/2024081356-mutable-everyday-6f9d@gregkh/
> > Link: https://lore.kernel.org/all/20240808154658.247873-1-herve.codina@bootlin.com/
> > 
> > Signed-off-by: Andrea della Porta <andrea.porta@...e.com>
> > Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>   # quirks.c, pci_ids.h
> 
> What changed in this patch so that you didn't include the Acked-by from Greg
> [1], or is this an oversight?

Nothing really, just an oversight. Thanks for spotting that out. I will resend V12
with it as I also notice that are some inconsistencies with mail Message-id, as a
result of subseqeunt invokation of git-format-patch from different branch.

Thanks,
Andrea

> 
> Regards,
> Matthias
> 
> [1] https://lore.kernel.org/linux-arm-kernel/2025042551-agency-boozy-dc3b@gregkh/
>