Date:   Mon, 18 Jul 2022 20:40:14 +0200
From:   Christian Marangi <ansuelsmth@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [net-next RFC PATCH 1/4] net: dsa: qca8k: drop
 qca8k_read/write/rmw for regmap variant

On Mon, Jul 18, 2022 at 09:40:17PM +0300, Vladimir Oltean wrote:
> On Mon, Jul 18, 2022 at 07:55:26PM +0200, Christian Marangi wrote:
> > Sure.
> > When the regmap conversion was done at times, to limit patch delta it
> > was suggested to keep these function. This was to not get crazy with
> > eventual backports and fixes.
> > 
> > The logic here is:
> > As we are moving these function AND the function will use regmap api
> > anyway, we can finally drop them and user the regmap api directly
> > instead of these additional function.
> > 
> > When the regmap conversion was done, I pointed out that in the future
> > the driver had to be split in specific and common code and it was said
> > that only at that times there was a good reason to make all these
> > changes and drop these special functions.
> > 
> > Now these function are used by both setup function for qca8k and by
> > common function that will be moved to a different file.
> > 
> > 
> > If we really want I can skip the dropping of these function and move
> > them to qca8k common code.
> 
> I don't really have a preference, I just want to understand why you want
> to call regmap_read(priv->regmap) directly every time as opposed to
> qca8k_read(priv) which is shorter to type and allows more stuff to fit
> on one line.

The main reason is that it's one less function. qca8k_read calls
directly the regmap ops so it seems a good time to drop it.

> 
> I think if you run "make drivers/net/dsa/qca/qca8k.lst" and you look at
> the generated code listing before and after, you'll find it is identical
> (note, I haven't actually done that).
> 
> > An alternative is to keep them for qca8k specific code and migrate the
> > common function to regmap api.
> 
> No, that's silly and I can't even find a reason to do that.
> It's not like you're trying to create a policy to not call qca8k-common.c
> functions from qca8k-8xxx.c, right? That should work just fine (in this
> case, qca8k_read etc).

The idea of qca8k-common is to keep them as generilized as possible.
Considering ipq4019 will have a different way to write/read regs we can't
lock common function to specific implementation.

> 
> In fact, while typing this I realized that in your code structure,
> you'll have one struct dsa_switch_ops in qca8k-8xxx.c and another one in
> qca8k-ipq4019.c. But the vast majority of dsa_switch_ops are common,
> with the exception of .setup() which is switch-specific, correct?

Phylink ops will also be different as ipq4019 will have qsgmii and will
require some calibration logic.

> 
> Wouldn't you consider, as an alternative, to move the dsa_switch_ops
> structure to the common C file as well, and have a switch-specific
> (*setup) operation in the match_data structure? Or even much better,
> make the switch-specific ops as fine-grained as possible, rather than
> reimplementing the entire qca8k_setup() (note, I don't know how similar
> they are, but there should be as little duplication of logic as possible,
> the common code should dictate what there is to do, and the switch
> specific code just how to do it).
> 

qca8k_setup will require major investigation and I think it would be
better to do do a qca8k_setup generalization when ipq4019 will be
proposed.

On the other hand I like the idea of putting the qca8k ops in common.c
and make the driver adds the relevant specific options.
Think I will also move that to common.c. That would permit to keep
function static aka even less delta and less bloat in the header file.

(is it a problem if it won't be const?)

> > So it's really a choice of drop these additional function or keep using
> > them for the sake of not modifying too much source.
> > 
> > Hope it's clear now the reason of this change.
> 
> If I were to summarize your reason, it would be "because I prefer it
> that way and because now is a good time", right? That's fine with me,
> but I honestly didn't understand that while reading the commit message.

I have to be honest... Yes you are right... This is really my opinion
and I don't have a particular strong reason on why dropping them.

It's really that I don't like keeping function that are just leftover of
an old implementation. But my target here is not argue and find a
solution so it's OK for me if I should keep these compat function and
migrate them to common.c.

-- 
	Ansuel

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