Re: [PATCH v2] mtd: implement proper partition handling

From: Miquel Raynal <miquel.raynal@bootlin.com>
To: Richard Weinberger <richard@nod.at>
Cc: Boris Brezillon <boris.brezillon@collabora.com>,
	linux-mtd <linux-mtd@lists.infradead.org>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	Tudor Ambarus <Tudor.Ambarus@microchip.com>
Subject: Re: [PATCH v2] mtd: implement proper partition handling
Date: Thu, 9 Jan 2020 19:45:56 +0100	[thread overview]
Message-ID: <20200109194556.34cf67dc@xps13> (raw)
In-Reply-To: <1737779363.17836.1578595384783.JavaMail.zimbra@nod.at>

Hi Richard,

Richard Weinberger <richard@nod.at> wrote on Thu, 9 Jan 2020 19:43:04
+0100 (CET):

> Miquel,
> 
> ----- Ursprüngliche Mail -----
> >> What problem does this solve?
> >> ...beside of a nice diffstat which removes more than it adds. :-)  
> > 
> > It is much easier to escalade to the top most "master" device when
> > there are multiple levels of partitioning, which was not cleanly
> > described IMHO. Also it is already used in the MLC-in-pseudo-SLC-mode
> > series :)  
> 
> Ok. In fact I "found" this patch my looking at the SLC emulation patches.
> 
> >> > +static inline struct mtd_info *mtd_get_master(struct mtd_info *mtd)
> >> > +{
> >> > +	while (mtd->parent)
> >> > +		mtd = mtd->parent;
> >> > +
> >> > +	return mtd;
> >> > +}  
> >> 
> >> So, parent == master?  
> > 
> > top most parent (the one without parent) == master !
> >   
> >> 
> >> When I create a MTD ontop of UBI using gluebi, who will be parent/master?  
> > 
> > I don't really understand the issue here?  
> 
> Let's say I have mtd0 with an ubi and a volume "xxx". After enabling
> gluebi a new mtd1 will arrive on the system.
> The stacking is mtd0 -> ubi (volume xxx) -> mtd1.

This is much clearer, thanks!

> Is now a relationship between mtd1 and mtd0?

No there is none. 

> I'd expect mtd1's parent being mtd0.

This would be a new feature, right? I don't think it is the case today.

Thanks,
Miquèl

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