linux-kernel - Re: [PATCH v5 4/4] mtd: Add driver for concatenating devices

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Message-ID: <431e7345-ee60-6d79-7a0c-9396da93029c@ti.com>
Date:   Wed, 4 Dec 2019 18:25:48 +0530
From:   Vignesh Raghavendra <vigneshr@...com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
CC:     Richard Weinberger <richard@....at>,
        Tudor Ambarus <Tudor.Ambarus@...rochip.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        <linux-mtd@...ts.infradead.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Bernhard Frauendienst <kernel@...pam.obeliks.de>
Subject: Re: [PATCH v5 4/4] mtd: Add driver for concatenating devices



On 04/12/19 3:47 pm, Miquel Raynal wrote:
> Hi Vignesh,
> 
> Vignesh Raghavendra <vigneshr@...com> wrote on Wed, 4 Dec 2019 15:28:46
> +0530:
> 
[...]
>> IIUC flash0 and flash1 are subnodes of a SPI master node?
>> And I believe flash0 node's compatible is "jedec,spi-nor"?
> 
> Indeed this is one possibility (probably the most common) but in theory
> this should work for any kind of MTD device, hence I voluntarily
> dropped the hardware-specific properties to focus on the partitions
> description here.
> 

Ah, make sense...

>>
>>
>>>
>>>         flash1 {
>>>                 partitions {
>>>                         compatible = "fixed-partitions";
>>>
>>> 			flash0_part1: part1@0 {  
>>
>> s/flash0_part1/flash1_part0?
> 
> Right!
> 
>>
>>> 				label = "part1_0";
>>> 				reg = <0x0 0x800000>;
>>> 			};
>>>
>>> 			part0@...000 {
>>> 				label = "part1_1";
>>> 				reg = <0x800000 0x800000>;
>>> 			};
>>>                 };
>>>         };
>>>   
>>
>> For my understanding, how many /dev/mtdX entries would this create?
> 
> If the master is retained (Kconfig option) and thanks to the common
> partitioning scheme, we would have:
> * flash0 (mtd0)
> *   part0_0 (mtd1)
> *   part0_1 (mtd2)
> * flash1 (mtd3)
> *   part1_0 (mtd4)
> *   part1_1 (mtd5)
> 
> If we enable this driver, we would also get an additional device:
> * mtd2-mtd4-concat (or part0_1-part1_0-concat, I don't recall the exact
>   name) being mtd6.

Ok, thanks for the clarification!


-- 
Regards
Vignesh