linux-kernel - Re: [PATCH v3 2/6] nvme: assign of

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Message-ID: <66b22499.170a0220.cc48.fa2b@mx.google.com>
Date: Tue, 6 Aug 2024 15:26:45 +0200
From: Christian Marangi <ansuelsmth@...il.com>
To: Christoph Hellwig <hch@....de>
Cc: Ulf Hansson <ulf.hansson@...aro.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Miquel Raynal <miquel.raynal@...tlin.com>,
	Richard Weinberger <richard@....at>,
	Vignesh Raghavendra <vigneshr@...com>,
	Joern Engel <joern@...ybastard.org>,
	Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...nel.dk>,
	Sagi Grimberg <sagi@...mberg.me>,
	Wolfram Sang <wsa+renesas@...g-engineering.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
	linux-mmc@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mtd@...ts.infradead.org,
	linux-nvme@...ts.infradead.org
Subject: Re: [PATCH v3 2/6] nvme: assign of_node to nvme device

On Tue, Aug 06, 2024 at 03:09:38PM +0200, Christoph Hellwig wrote:
> On Tue, Aug 06, 2024 at 03:03:24PM +0200, Christian Marangi wrote:
> > Well on embedded pure PCIe card most of the time are not a thing...
> > Unless it's an enterprise product, everything is integrated in the pcb
> > and not detachable for cost saving measure or also if the thing use PCIe
> > protocol but it tighlty coupled with the SoC.
> 
> Yes, PCIe has a bunch of form factors, including just soldered on BGA
> devices, but none of that matters at all for the logical protocol.
>

Correct, for the context of soldered stuff tho things can be
malfunctioning (problem in the PCIe driver) or working so it's possibile
to make assumption and attach OF node in DT. Consider that the thing is
probed only if the card is correctly detected. Card not present ->
nothing is done.

> > This implementation is already very common for all kind of pcie devices
> > like wireless card, gpio expander that are integrated in the PCB and
> > require property in DT like calibration data, quirks or GPIO pin
> > definitions, i2c...
> 
> Do you have a document on that/
> 

You mean example of PCIe that makes use of OF? Pretty much ath10k-11k
mediatek and in general all wireless card. Example ath11k-pci.yaml [1]

Compatible is set to the ID. PCIe will attach an OF node if found in the
pcie child nodes (already supported)

On NVMe driver side, the NVMe controller will already have an OF node
present.

We are now just adding an additional subnode "nvme-card" and attach it
on the root disk when it's created.

[1] https://github.com/torvalds/linux/blob/master/Documentation/devicetree/bindings/net/wireless/qcom%2Cath11k-pci.yaml

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