linux-kernel - Re: [PATCH v12 3/3] mtd: Add driver for concatenating devices

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Message-ID: <87o6vyjgfl.fsf@bootlin.com>
Date: Mon, 12 May 2025 12:01:50 +0200
From: Miquel Raynal <miquel.raynal@...tlin.com>
To: "Mahapatra, Amit Kumar" <amit.kumar-mahapatra@....com>
Cc: "richard@....at" <richard@....at>,  "vigneshr@...com" <vigneshr@...com>,
  "robh@...nel.org" <robh@...nel.org>,  "krzk+dt@...nel.org"
 <krzk+dt@...nel.org>,  "conor+dt@...nel.org" <conor+dt@...nel.org>,
  "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
  "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
  "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,  "git
 (AMD-Xilinx)" <git@....com>,  "amitrkcian2002@...il.com"
 <amitrkcian2002@...il.com>,  Bernhard Frauendienst
 <kernel@...pam.obeliks.de>
Subject: Re: [PATCH v12 3/3] mtd: Add driver for concatenating devices


>> > +           mtd->dev.parent = concat->subdev[0]->dev.parent;
>> > +           mtd->dev = concat->subdev[0]->dev;
>> > +
>> > +           /* Register the platform device */
>> > +           ret = mtd_device_register(mtd, NULL, 0);
>> > +           if (ret)
>> > +                   goto destroy_concat;
>> > +   }
>> > +
>> > +   return 0;
>> > +
>> > +destroy_concat:
>> > +   mtd_concat_destroy(mtd);
>> > +
>> > +   return ret;
>> > +}
>> > +
>> > +late_initcall(mtd_virt_concat_create_join);
>>
>> The current implementation does not support probe deferrals, I believe it should be
>> handled.
>
> I see that the parse_mtd_partitions() API can return -EPROBE_DEFER during
> MTD device registration, but this behavior is specific to the
> parse_qcomsmem_part parser. None of the other parsers appear to support
> probe deferral. As discussed in RFC [1], the virtual concat feature is
> purely a fixed-partition capability, and based on my understanding, the
> fixed-partition parser does not support probe deferral.
> Please let me know if you can think of any other probe deferral scenarios
> that might impact the virtual concat driver.

That's true, but I kind of dislike the late_initcall, I fear it might
break in creative ways.

Thanks,
Miquèl