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Date:   Mon, 12 Sep 2022 14:03:43 -0700
From:   Colin Foster <colin.foster@in-advantage.com>
To:     Vladimir Oltean <vladimir.oltean@nxp.com>
Cc:     "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Russell King <linux@armlinux.org.uk>,
        Paolo Abeni <pabeni@redhat.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Eric Dumazet <edumazet@google.com>,
        "David S. Miller" <davem@davemloft.net>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Vivien Didelot <vivien.didelot@gmail.com>,
        Andrew Lunn <andrew@lunn.ch>,
        "UNGLinuxDriver@microchip.com" <UNGLinuxDriver@microchip.com>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Claudiu Manoil <claudiu.manoil@nxp.com>,
        Lee Jones <lee@kernel.org>
Subject: Re: [RFC v1 net-next 7/8] mfd: ocelot: add regmaps for ocelot_ext
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On Mon, Sep 12, 2022 at 08:23:21PM +0000, Vladimir Oltean wrote:
> On Mon, Sep 12, 2022 at 12:04:45PM -0700, Colin Foster wrote:
> > That is exactly right. The ocelot_ext version of init_regmap() now uses
> > dev_get_regmap() which only cares about the name and essentially drops
> > the rest of the information. Previous versions hooked into the
> > ocelot-core / ocelot-spi MFD system to request that a new regmap be
> > created (with start and end being honored.) A benefit of this design is
> > that any regmaps that are named the same are automatically shared. A
> > drawback (or maybe a benefit?) is that the users have no control over
> > ranges / flags.
> > 
> > I think if this goes the way of index-based that'll work. I'm happy to
> > revert my previous change (sorry it snuck in) but it seems like there'll
> > still have to be some trickery... For reference:
> > 
> > enum ocelot_target {
> > 	ANA = 1,
> > 	QS,
> > 	QSYS,
> > 	REW,
> > 	SYS,
> > 	S0,
> > 	S1,
> > 	S2,
> > 	HSIO,
> > 	PTP,
> > 	FDMA,
> > 	GCB,
> > 	DEV_GMII,
> > 	TARGET_MAX,
> > };
> > 
> > mfd_add_devices will probably need to add a zero-size resource for HSIO,
> > PTP, FDMA, and anything else that might come along in the future. At
> > this point, regmap_from_mfd(PTP) might have to look like (pseudocode):
> > 
> > struct regmap *ocelot_ext_regmap_from_mfd(struct ocelot *ocelot, int index)
> > {
> >     return ocelot_regmap_from_resource_optional(pdev, index-1, config);
> > 
> >     /* Note this essentially expands to:
> >      * res = platform_get_resource(pdev, IORESOURCE_REG, index-1);
> >      * return dev_get_regmap(pdev->dev.parent, res->name);
> >      *
> >      * This essentially throws away everything that my current
> >      * implementation does, except for the IORESOURCE_REG flag
> >      */
> > }
> > 
> > Then drivers/net/dsa/felix.c felix_init_structs() would have two loops
> > (again, just as an example)
> > 
> > for (i = ANA; i < TARGET_MAX; i++) {
> >     if (felix->info->regmap_from_mfd)
> >         target = felix->info->regmap_from_mfd(ocelot, i);
> >     else {
> >         /* existing logic back to ocelot_regmap_init() */
> >     }
> > }
> > 
> > for (port = 0; port < num_phys_ports; port++) {
> >     ...
> >     if (felix->info->regmap_from_mfd)
> >         target = felix->info->regmap_from_mfd(ocelot, TARGET_MAX + port);
> >     else {
> >         /* existing logic back to ocelot_regmap_init() */
> >     }
> > }
> > 
> > And lastly, ocelot_core_init() in drivers/mfd/ocelot-core.c would need a
> > mechanism to say "don't add a regmap for cell->resources[PTP], even
> > though that resource exists" because... well I suppose it is only in
> > drivers/net/ethernet/mscc/ocelot_vsc7514.c for now, but the existance of
> > those regmaps invokes different behavior. For instance:
> > 
> > 	if (ocelot->targets[FDMA])
> > 		ocelot_fdma_init(pdev, ocelot);
> > 
> > I'm not sure whether this last point will have an effect on felix.c in
> > the end. My current patch set of adding the SERDES ports uses the
> > existance of targets[HSIO] to invoke ocelot_pll5_init() similar to the
> > ocelot_vsc7514.c FDMA / PTP conditionals, but I'd understand if that
> > gets rejected outright. That's for another day.
> > 
> > 
> > 
> > I'm happy to make these changes if you see them valid. I saw the fact
> > that dev_get_regmap(dev->parent, res->name) could be used directly in
> > ocelot_ext_regmap_init() as an elegant solution to felix / ocelot-lib /
> > ocelot-core, but I recognize that the subtle "throw away the
> > IORESOURCE_MEM flag and res->{start,end} information" isn't ideal.
> 
> Thinking some more about it, there will have to be even more trickery.
> Say you solve the problem for the global targets, but then what do you
> do for the port targets, how do you reference those by index?
> TARGET_MAX + port? Hmm, that isn't great either.

Yep, that's what my example above shows. Not my favorite.

> 
> What if we meet half way, and you just get the resources from the
> platform device by name, instead of by index? You'd have to modify the
> regmap creation procedure to look at a predefined array of strings,
> containing names of all targets that are mandatory (a la mscc_ocelot_probe),
> and match those
> (a) iteration over target_io_res and strcmp(), in the case of vsc9959
>     and vsc9953
> (b) dev_get_regmap() in the case of ocelot_ext
> 
> This way there's still no direct communication between ocelot-mfd and
> DSA, and I have the feeling that the problems we both mention are
> solved. Hope I'm not missing something.

This sounds reasonable. So long as it doesn't muddy up felix / seville
too much - I'll take a look. It seems like it would just be moving
a lot of the "resource configuration" code from felix_init_structs() into
the felix->info->init_regmap(), or similar.