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Date: Tue, 11 Jan 2022 10:28:15 -0800 From: Colin Foster <colin.foster@...advantage.com> To: Lee Jones <lee.jones@...aro.org> Cc: Mark Brown <broonie@...nel.org>, linux-gpio@...r.kernel.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, Linus Walleij <linus.walleij@...aro.org>, Russell King <linux@...linux.org.uk>, Heiner Kallweit <hkallweit1@...il.com>, Jakub Kicinski <kuba@...nel.org>, "David S. Miller" <davem@...emloft.net>, Florian Fainelli <f.fainelli@...il.com>, Vivien Didelot <vivien.didelot@...il.com>, Andrew Lunn <andrew@...n.ch>, UNGLinuxDriver@...rochip.com, Alexandre Belloni <alexandre.belloni@...tlin.com>, Claudiu Manoil <claudiu.manoil@....com>, Vladimir Oltean <vladimir.oltean@....com> Subject: Re: [RFC v5 net-next 01/13] mfd: ocelot: add support for external mfd control over SPI for the VSC7512 Hi Lee, On Tue, Jan 11, 2022 at 05:00:11PM +0000, Lee Jones wrote: > On Tue, 11 Jan 2022, Colin Foster wrote: > > > Hi Mark and Lee, > > > > > > > > > However, even if that is required, I still think we can come up with > > > > something cleaner than creating a whole API based around creating > > > > and fetching different regmap configurations depending on how the > > > > system was initialised. > > > > > > Yeah, I'd expect the usual pattern is to have wrapper drivers that > > > instantiate a regmap then have the bulk of the driver be a library that > > > they call into should work. > > > > Understood. And I think this can make sense and clean things up. The > > "ocelot_core" mfd will register every regmap range, regardless of > > whether any child actually uses them. Every child can then get regmaps > > by name, via dev_get_regmap. That'll get rid of the back-and-forth > > regmap hooks. > > I was under the impression that MFD would not always be used? > > Didn't you have a use-case where the child devices could be used > independently of anything else? > > If not, why don't you just register a single Regmap covering the whole > range? Then let the Regmap API deal with the concurrency handling. That's exactly the use-case I was considering. An example: "mscc,ocelot-miim" exists. It can currently be used in two different scenarios: directly with devicetree, or indirectly as in drivers/net/dsa/ocelot/seville_vsc9953.c mscc_miim_setup(dev, &bus, "VSC9953 internal MDIO bus", ocelot->targets[GCB], ocelot->map[GCB][GCB_MIIM_MII_STATUS & REG_MASK]); The "GCB_MIIM_MII_STATUS" parameter is the offset from the base for that regmap. See commit (b99658452355 "net: dsa: ocelot: felix: utilize shared mscc-miim driver for indirect…") (My apologies if the formatting of that commit refernece is incorrect) But in that case... the Seville driver makes a devcpu_gcb regmap located at 0x71070000. That regmap is created over the entire "GCB range". That gets passed into the mscc-miim driver, along with the base register location of the MIIM periperal. At the same time, mscc-miim can be probed independently, at which point it would create a smaller regmap at 0x7107009c (Documentation/devicetree/bindings/mscc-miim.txt) So the mscc-miim driver supports multiple use-cases. I expect the same type of "offset" idea can be reasonably added to the following drivers, all of which already exist but need to support the same type of use-case: mscc,ocelot-pinctrl, mscc,ocelot-sgpio, mscc,ocelot-miim, and mscc,vsc7514-serdes. As I'm bringing up different parts of the hardware, there might be more components that become necessary. With the exception of vsc7514-serdes, those all exist outside of MFD. The vsc7512-serdes driver currently relies on syscon / MFD, which adds a different complexity. One that I think probably merits a separate probe function. > > -- > Lee Jones [李琼斯] > Principal Technical Lead - Developer Services > Linaro.org │ Open source software for Arm SoCs > Follow Linaro: Facebook | Twitter | Blog
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