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

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Message-ID: <ceab3813dad635387e9f216203292fbe@manjaro.org>
Date: Tue, 06 Aug 2024 17:39:32 +0200
From: Dragan Simic <dsimic@...jaro.org>
To: Christian Marangi <ansuelsmth@...il.com>
Cc: Christoph Hellwig <hch@....de>, 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

Hello all,

On 2024-08-06 15:03, Christian Marangi wrote:
> On Tue, Aug 06, 2024 at 02:43:12PM +0200, Christoph Hellwig wrote:
>> On Tue, Aug 06, 2024 at 01:41:12PM +0200, Christian Marangi wrote:
>> > Introduce support for a dedicated node for a nvme card. This will be a
>> > subnode of the nvme controller node that will have the "nvme-card"
>> > compatible.
>> >
>> > This follow a similar implementation done for mmc where the specific mmc
>> > card have a dedicated of_node.
>> >
>> > This can be used for scenario where block2mtd module is used to declare
>> > partition in DT and block2mtd is called on the root block of the nvme
>> > card, permitting the usage of fixed-partition parser or alternative
>> > ones.
>> 
>> Err, hell no.  Why would you wire up a purely PCIe device to OF?
>> PCIe is self-discovering.
>> 
> 
> 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.
> 
> 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...
> 
> In modern SoC we are seeing an influx of using cheap flash storage
> option instead of NAND or NOR as modern hw require more space and price
> increase is not that high... Almost any high tier device is switching 
> to
> using emmc and even attached NVME and simulating MTD with them for easy
> usage.
> 
> Please consider this well used scenario in emebedded where PCIe is just
> a comunication way and the concept of detachable doesn't exist at all
> and things can be described in DT as static. Also these storage are 
> used
> for rootfs mount so userspace is not so viable.

As a note, perhaps this is another good example of a "fixed layout"
PCIe device found on an SBC:

https://lore.kernel.org/linux-rockchip/20240805073425.3492078-1-jacobe.zang@wesion.com/T/#u