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

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Message-ID: <20231008153919.5b8e2562@xps-13>
Date:   Sun, 8 Oct 2023 15:39:19 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Rafał Miłecki <rafal@...ecki.pl>
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

Hi Rafał,

rafal@...ecki.pl wrote on Sat, 07 Oct 2023 18:09:06 +0200:

> 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?

Yeah would work as well. But I will just get rid of this, with your
other patch that solves the fact that of_node will be there with mtd
devices, it's no longer relevant.

Thanks,
Miquèl