linux-kernel - Re: [PATCH v8 08/13] misc: rp1: RaspberryPi RP1 misc driver

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Message-ID: <20250416193152.GA78446@bhelgaas>
Date: Wed, 16 Apr 2025 14:31:52 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
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-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 v8 08/13] misc: rp1: RaspberryPi RP1 misc driver

On Wed, Mar 19, 2025 at 10:52:29PM +0100, 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

> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index b84ff7bade82..4dfda527c76b 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -6283,6 +6283,7 @@ DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_XILINX, 0x5020, of_pci_make_dev_node);
>  DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_XILINX, 0x5021, of_pci_make_dev_node);
>  DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_REDHAT, 0x0005, of_pci_make_dev_node);
>  DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_EFAR, 0x9660, of_pci_make_dev_node);
> +DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_RPI, PCI_DEVICE_ID_RPI_RP1_C0, of_pci_make_dev_node);
>  
>  /*
>   * Devices known to require a longer delay before first config space access
> diff --git a/include/linux/pci_ids.h b/include/linux/pci_ids.h
> index de5deb1a0118..b7a2c0fd589e 100644
> --- a/include/linux/pci_ids.h
> +++ b/include/linux/pci_ids.h
> @@ -2620,6 +2620,9 @@
>  #define PCI_VENDOR_ID_TEKRAM		0x1de1
>  #define PCI_DEVICE_ID_TEKRAM_DC290	0xdc29
>  
> +#define PCI_VENDOR_ID_RPI		0x1de4
> +#define PCI_DEVICE_ID_RPI_RP1_C0	0x0001
> +
>  #define PCI_VENDOR_ID_ALIBABA		0x1ded
>  
>  #define PCI_VENDOR_ID_CXL		0x1e98
> -- 
> 2.35.3
>