linux-kernel - Re: [PATCH v12 2/7] nvmem: Clarify the situation when there is no DT node available

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Message-ID: <2e3ea6a4e63e0c6bebf4c18b165250e5@milecki.pl>
Date:   Sat, 07 Oct 2023 18:09:06 +0200
From:   Rafał Miłecki <rafal@...ecki.pl>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Michael Walle <michael@...le.cc>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Robert Marko <robert.marko@...tura.hr>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Luka Perkov <luka.perkov@...tura.hr>,
        Randy Dunlap <rdunlap@...radead.org>,
        Chen-Yu Tsai <wenst@...omium.org>,
        Daniel Golle <daniel@...rotopia.org>
Subject: Re: [PATCH v12 2/7] nvmem: Clarify the situation when there is no DT
 node available

One comment below

On 2023-10-06 18:32, Miquel Raynal wrote:
> rafal@...ecki.pl wrote on Fri, 06 Oct 2023 13:41:52 +0200:
> 
>> On 2023-10-05 17:59, Miquel Raynal wrote:
>> > At a first look it might seem that the presence of the of_node pointer
>> > in the nvmem device does not matter much, but in practice, after > looking
>> > deep into the DT core, nvmem_add_cells_from_dt() will simply and always
>> > return NULL if this field is not provided. As most mtd devices don't
>> > populate this field (this could evolve later), it means none of their
>> > children cells will be populated unless no_of_node is explicitly set to
>> > false. In order to clarify the logic, let's add clear check at the
>> > beginning of this helper.
>> 
>> I'm somehow confused by above explanation and code too. I read it
>> carefully 5 times but I can't see what exactly this change helps with.
>> 
>> At first look at nvmem_add_cells_from_legacy_of() I can see it uses
>> "of_node" so I don't really agree with "it might seem that the 
>> presence
>> of the of_node pointer in the nvmem device does not matter much".
>> 
>> You really don't need to look deep into DT core (actually you don't 
>> have
>> to look into it at all) to understand that nvmem_add_cells_from_dt()
>> will return 0 (nitpicking: not NULL) for a NULL pointer. It's all made
>> of for_each_child_of_node(). Obviously it does nothing if there is
>> nothing to loop over.
> 
> That was not obvious to me as I thought it would start from /, which I
> think some other function do when you don't provide a start node.

What about documenting that function instead of adding redundant code?


>> Given that for_each_child_of_node() is NULL-safe I think code from 
>> this
>> patch is redundant.
> 
> I didn't say it was not safe, just not explicit.

-- 
Rafał Miłecki