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Message-ID: <affdcc33-7ffc-5368-727b-1382ec92007b@linaro.org>
Date:   Mon, 9 Oct 2023 10:44:56 +0100
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Subject: Re: [PATCH v12 2/7] nvmem: Clarify the situation when there is no DT
 node available
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To:     Miquel Raynal <miquel.raynal@bootlin.com>,
        =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?= <rafal@milecki.pl>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Michael Walle <michael@walle.cc>,
        Rob Herring <robh+dt@kernel.org>,
        Frank Rowand <frowand.list@gmail.com>,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        Robert Marko <robert.marko@sartura.hr>,
        Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
        Luka Perkov <luka.perkov@sartura.hr>,
        Randy Dunlap <rdunlap@infradead.org>,
        Chen-Yu Tsai <wenst@chromium.org>,
        Daniel Golle <daniel@makrotopia.org>
References: <20231005155907.2701706-1-miquel.raynal@bootlin.com>
 <20231005155907.2701706-3-miquel.raynal@bootlin.com>
 <05cd4592d0cfe0fb86aeb24db01de547@milecki.pl>
 <20231006183229.51cd8e60@xps-13>
From:   Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
In-Reply-To: <20231006183229.51cd8e60@xps-13>
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On 06/10/2023 17:32, Miquel Raynal wrote:
> Hi Rafał,
> 
> rafal@milecki.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.
> 
>> 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.
> 
>> Later you mention "no_of_node" which I agree to be a very non-intuitive
>> config option. As pointed in another thread I already sent:
>> [PATCH] Revert "nvmem: add new config option"
>> https://lore.kernel.org/lkml/ba3c419a-6511-480a-b5f2-6c418f9c02e7@gmail.com/t/
> 
> I actually wanted to find again that patch and could not get my hands on
> it, but it is probably a much better fix than my other mtd patch, I
> agree with you.
> 
>> Maybe with above patch finally things will get more clear and we don't
>> need this PATCH after all?
> 
> Yes. Srinivas, what are your plans for the above patch?

for_each_child_of_node is null safe, so this patch is really not adding 
much value TBH.

--srini
> 
> Thanks,
> Miquèl