linux-kernel - Re: [RFC PATCH 3/4] block: add support for partition table defined in OF

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Message-ID: <66fbc042.050a0220.3523ed.a6f9@mx.google.com>
Date: Tue, 1 Oct 2024 11:26:22 +0200
From: Christian Marangi <ansuelsmth@...il.com>
To: Christoph Hellwig <hch@...radead.org>
Cc: Jens Axboe <axboe@...nel.dk>, Jonathan Corbet <corbet@....net>,
	Ulf Hansson <ulf.hansson@...aro.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	INAGAKI Hiroshi <musashino.open@...il.com>,
	Daniel Golle <daniel@...rotopia.org>,
	Christian Brauner <brauner@...nel.org>,
	Al Viro <viro@...iv.linux.org.uk>, Ming Lei <ming.lei@...hat.com>,
	Li Lingfeng <lilingfeng3@...wei.com>,
	Christian Heusel <christian@...sel.eu>, linux-block@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mmc@...r.kernel.org, devicetree@...r.kernel.org,
	Miquel Raynal <miquel.raynal@...tlin.com>,
	Lorenzo Bianconi <lorenzo@...nel.org>
Subject: Re: [RFC PATCH 3/4] block: add support for partition table defined
 in OF

On Tue, Oct 01, 2024 at 01:37:05AM -0700, Christoph Hellwig wrote:
> On Tue, Sep 24, 2024 at 12:17:36PM +0200, Christian Marangi wrote:
> > On Mon, Sep 23, 2024 at 11:34:53PM -0700, Christoph Hellwig wrote:
> > > On Mon, Sep 23, 2024 at 12:59:32PM +0200, Christian Marangi wrote:
> > > > +#define BOOT0_STR	"boot0"
> > > > +#define BOOT1_STR	"boot1"
> > > > +
> > > 
> > > This boot0/1 stuff looks like black magic, so it should probably be
> > > documented at very least.
> > >
> > 
> > It is but from what I have read in the spec for flash in general (this
> > is not limited to eMMC but also apply to UFS) these are hardware
> > partition. If the version is high enough these are always present and
> > have boot0 and boot1 name hardcoded by the driver.
> 
> How does this belong into generic block layer code?
>

(just as an info, we are at v4 where I added more info about this)

The cmdline partition parser supports this already, just not clearly
stated in the code but described in the Documentation example and info.

> > > > +	partitions_np = get_partitions_node(disk_np,
> > > > +					    state->disk->disk_name);
> > > 
> > > disk->disk_name is not a stable identifier and can change from boot to
> > > boot due to async probing.  You'll need to check a uuid or label instead.
> > 
> > This is really for the 2 special partition up to check the suffix, we
> > don't really care about the name. I guess it's acceptable to use
> > unstable identifier?
> 
> No.  ->disk_name is in no way reliable, we can't hardcode that into
> a partition parser.
> 

Then any hint on this or alternative way?
Again this is how it's done with cmdline partition so I'm just following
how it's already done.

Also I feel it's not clear enough that we really don't care about the
identifier, eMMC driver hardcode and always append to disk_name boot0, boot1,
the fact that one disk or another might have a different identifier and
they change on different boot is not important for the task needed here.

I can drop this thing entirely and make the implementation very simple
but there are already request and happy dev that would benefits for the
additional hardware partition supported by this.

-- 
	Ansuel