From: Lee Jones <lee.jones@linaro.org>
To: Colin Foster <colin.foster@in-advantage.com>
Cc: linux-gpio@vger.kernel.org, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org,
Linus Walleij <linus.walleij@linaro.org>,
Russell King <linux@armlinux.org.uk>,
Heiner Kallweit <hkallweit1@gmail.com>,
Jakub Kicinski <kuba@kernel.org>,
"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,
Alexandre Belloni <alexandre.belloni@bootlin.com>,
Claudiu Manoil <claudiu.manoil@nxp.com>,
Vladimir Oltean <vladimir.oltean@nxp.com>
Subject: Re: [RFC v5 net-next 08/13] mfd: add interface to check whether a device is mfd
Date: Mon, 10 Jan 2022 12:23:09 +0000 [thread overview]
Message-ID: <YdwlLYFPU16roS8E@google.com> (raw)
In-Reply-To: <20211230201253.GA1484230@euler>
On Thu, 30 Dec 2021, Colin Foster wrote:
> On Thu, Dec 30, 2021 at 01:43:53PM +0000, Lee Jones wrote:
> > On Wed, 29 Dec 2021, Colin Foster wrote:
> >
> > > On Wed, Dec 29, 2021 at 03:25:55PM +0000, Lee Jones wrote:
> > > > On Sat, 18 Dec 2021, Colin Foster wrote:
> > > >
> > > > > Some drivers will need to create regmaps differently based on whether they
> > > > > are a child of an MFD or a standalone device. An example of this would be
> > > > > if a regmap were directly memory-mapped or an external bus. In the
> > > > > memory-mapped case a call to devm_regmap_init_mmio would return the correct
> > > > > regmap. In the case of an MFD, the regmap would need to be requested from
> > > > > the parent device.
> > > > >
> > > > > This addition allows the driver to correctly reason about these scenarios.
> > > > >
> > > > > Signed-off-by: Colin Foster <colin.foster@in-advantage.com>
> > > > > ---
> > > > > drivers/mfd/mfd-core.c | 5 +++++
> > > > > include/linux/mfd/core.h | 10 ++++++++++
> > > > > 2 files changed, 15 insertions(+)
> > > > >
> > > > > diff --git a/drivers/mfd/mfd-core.c b/drivers/mfd/mfd-core.c
> > > > > index 684a011a6396..905f508a31b4 100644
> > > > > --- a/drivers/mfd/mfd-core.c
> > > > > +++ b/drivers/mfd/mfd-core.c
> > > > > @@ -33,6 +33,11 @@ static struct device_type mfd_dev_type = {
> > > > > .name = "mfd_device",
> > > > > };
> > > > >
> > > > > +int device_is_mfd(struct platform_device *pdev)
> > > > > +{
> > > > > + return (!strcmp(pdev->dev.type->name, mfd_dev_type.name));
> > > > > +}
> > > > > +
> > > >
> > > > Why is this device different to any other that has ever been
> > > > mainlined?
> > >
> > > Hi Lee,
> > >
> > > First, let me apologize for not responding to your response from the
> > > related RFC from earlier this month. It had been blocked by my spam
> > > filter and I had not seen it until just now. I'll have to check that
> > > more diligently now.
> > >
> > > Moving on...
> > >
> > > That's a question I keep asking myself. Either there's something I'm
> > > missing, or there's something new I'm doing.
> > >
> > > This is taking existing drivers that work via MMIO regmaps and making
> > > them interface-independent. As Vladimir pointed out here:
> > > https://lore.kernel.org/all/20211204022037.dkipkk42qet4u7go@skbuf/T/
> > > device_is_mfd could be dropped in lieu of an mfd-specific probe
> > > function.
> > >
> > > If there's something I'm missing, please let me know. But it feels like
> > > devm_get_regmap_from_resource at the end of the day would be the best
> > > solution to the design, and that doesn't exist. And implementing
> > > something like that is a task that I feel I'm not capable of tackling at
> > > this time.
> >
> > I'm really not a fan of leaking any MFD API outside of drivers/mfd.
> > MFD isn't a tangible thing. It's a Linuxiusm, something we made up, a
> > figment of your imagination.
> >
> > What happens if you were to all dev_get_regmap() in the non-MFD case
> > or when you call devm_regmap_init_mmio() when the driver was
> > registered via the MFD framework?
>
> I'd imagine dev_get_regmap in a non-MFD case would be the same as
> dev_get_and_ioremap_resource() followed by devm_regmap_init_mmio().
>
> In the MFD case it would possibly request the regmap from the parent,
> which could reason about how to create the regmap. As you understand,
> this is exactly the behavior I created in this patch set. I did it by
> way of ocelot_get_regmap_from_resource, and admit it isn't the best way.
> But it certainly seems there isn't an existing method that I'm missing.
>
> I'm coming from a pretty narrow field of view, but believe my use-case
> is a valid one. If that is true, and there isn't another design I should
> use... this is the opportunity to create it. Implementing
> ocelot_get_regmap_from_resource is a way to achieve my needs without
> affecting anyone else.
>
> Going one step further and implementing mfd_get_regmap_from_parent (or
> similar) would creep into the design of MFD. I don't know enough about
> MFD and the users to suggest this. I wouldn't want to start venturing
> down that path without blessing from the community. And this would
> indirectly affect every MFD driver.
>
> Going all in and implementing device_get_regmap_from_resource... I don't
> know that I'd be comfortable even starting down that path knowing that
> it would affect every device. Perhaps it would have to utilize something
> like IORESOURCE_REG that seems to only get utilized in a handful of
> files:
> https://elixir.bootlin.com/linux/v5.16-rc7/C/ident/IORESOURCE_REG
Let's speak to Mark and see if he can provide any insight.
--
Lee Jones [李琼斯]
Principal Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
Follow Linaro: Facebook | Twitter | Blog
next prev parent reply other threads:[~2022-01-10 12:23 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-18 21:49 [RFC v5 net-next 00/13] add support for VSC75XX control over SPI Colin Foster
2021-12-18 21:49 ` [RFC v5 net-next 01/13] mfd: ocelot: add support for external mfd control over SPI for the VSC7512 Colin Foster
2021-12-29 15:22 ` Lee Jones
2021-12-30 1:43 ` Colin Foster
2022-01-10 12:16 ` Lee Jones
2022-01-11 0:33 ` Colin Foster
2022-01-11 10:13 ` Lee Jones
2022-01-11 13:44 ` Mark Brown
2022-01-11 16:53 ` Colin Foster
2022-01-11 17:00 ` Lee Jones
2022-01-11 18:28 ` Colin Foster
2022-01-11 18:41 ` Alexandre Belloni
2022-01-15 2:07 ` Colin Foster
2021-12-18 21:49 ` [RFC v5 net-next 02/13] mfd: ocelot: offer an interface for MFD children to get regmaps Colin Foster
2021-12-29 15:23 ` Lee Jones
2021-12-29 19:34 ` Alexandre Belloni
2021-12-29 20:12 ` Lee Jones
2021-12-18 21:49 ` [RFC v5 net-next 03/13] net: mscc: ocelot: expose ocelot wm functions Colin Foster
2021-12-18 21:49 ` [RFC v5 net-next 04/13] net: dsa: felix: add configurable device quirks Colin Foster
2021-12-18 21:49 ` [RFC v5 net-next 05/13] net: mdio: mscc-miim: add ability to externally register phy reset control Colin Foster
2021-12-18 21:49 ` [RFC v5 net-next 06/13] net: dsa: ocelot: add external ocelot switch control Colin Foster
2021-12-18 21:49 ` [RFC v5 net-next 07/13] mfd: ocelot: enable the external switch interface Colin Foster
2021-12-29 15:24 ` Lee Jones
2021-12-18 21:49 ` [RFC v5 net-next 08/13] mfd: add interface to check whether a device is mfd Colin Foster
2021-12-29 15:25 ` Lee Jones
2021-12-30 2:04 ` Colin Foster
2021-12-30 13:43 ` Lee Jones
2021-12-30 20:12 ` Colin Foster
2022-01-10 12:23 ` Lee Jones [this message]
2021-12-18 21:49 ` [RFC v5 net-next 09/13] net: mdio: mscc-miim: add local dev variable to cleanup probe function Colin Foster
2021-12-18 21:49 ` [RFC v5 net-next 10/13] net: mdio: mscc-miim: add MFD functionality through ocelot-core Colin Foster
2021-12-18 21:49 ` [RFC v5 net-next 11/13] mfd: ocelot-core: add control for the external mdio interface Colin Foster
2021-12-29 15:26 ` Lee Jones
2021-12-18 21:49 ` [RFC v5 net-next 12/13] pinctrl: ocelot: add MFD functionality through ocelot-core Colin Foster
2021-12-18 21:49 ` [RFC v5 net-next 13/13] mfd: ocelot: add ocelot-pinctrl as a supported child interface Colin Foster
2021-12-29 15:26 ` Lee Jones
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