From: Michael Walle <michael@walle.cc>
To: Lee Jones <lee.jones@linaro.org>
Cc: devicetree@vger.kernel.org, arnd@arndb.de,
gregkh@linuxfoundation.org, linus.walleij@linaro.org,
linux-kernel@vger.kernel.org, robh+dt@kernel.org,
Wolfram Sang <wsa@kernel.org>,
bgolaszewski@baylibre.com, broonie@kernel.org,
andriy.shevchenko@linux.intel.com,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v4 1/1] mfd: Add I2C based System Configuaration (SYSCON) access
Date: Thu, 02 Jul 2020 11:12:56 +0200 [thread overview]
Message-ID: <58ae64ebf22707ad1725987615b355c2@walle.cc> (raw)
In-Reply-To: <20200702081825.GR1179328@dell>
Am 2020-07-02 10:18, schrieb Lee Jones:
> On Thu, 02 Jul 2020, Michael Walle wrote:
>
>> Am 2020-07-02 08:54, schrieb Lee Jones:
>> > On Wed, 01 Jul 2020, Michael Walle wrote:
>> >
>> > > Am 2020-07-01 09:04, schrieb Lee Jones:
>> > > > On Wed, 01 Jul 2020, Michael Walle wrote:
>> > > >
>> > > > > Hi Lee,
>> > > > >
>> > > > > Am 2020-06-30 11:16, schrieb Michael Walle:
>> > > > > > I'm just trying to use this for my sl28 driver. Some remarks, see below.
>> > > > > >
>> > > > > > Am 2020-06-22 09:51, schrieb Lee Jones:
>> > > > > > > The existing SYSCON implementation only supports MMIO (memory mapped)
>> > > > > > > accesses, facilitated by Regmap. This extends support for registers
>> > > > > > > held behind I2C busses.
>> > > > > > >
>> > > > > > > Signed-off-by: Lee Jones <lee.jones@linaro.org>
>> > > > > > > ---
>> > > > > > > Changelog:
>> > > > > > >
>> > > > > > > v3 => v4
>> > > > > > > - Add ability to provide a non-default Regmap configuration
>> > > > > > >
>> > > > > > > v2 => v3
>> > > > > > > - Change 'is CONFIG' present check to include loadable modules
>> > > > > > > - s/#ifdef CONFIG_MFD_SYSCON_I2C/#if
>> > > > > > > IS_ENABLED(CONFIG_MFD_SYSCON_I2C)/
>> > > > > > >
>> > > > > > > v1 => v2
>> > > > > > > - Remove legacy references to OF
>> > > > > > > - Allow building as a module (fixes h8300 0-day issue)
>> > > > > > >
>> > > > > > > drivers/mfd/Kconfig | 7 +++
>> > > > > > > drivers/mfd/Makefile | 1 +
>> > > > > > > drivers/mfd/syscon-i2c.c | 104
>> > > > > > > +++++++++++++++++++++++++++++++++
>> > > > > > > include/linux/mfd/syscon-i2c.h | 36 ++++++++++++
>> > > > > > > 4 files changed, 148 insertions(+)
>> > > > > > > create mode 100644 drivers/mfd/syscon-i2c.c
>> > > > > > > create mode 100644 include/linux/mfd/syscon-i2c.h
>> >
>> > [...]
>> >
>> > > > > > This way, (a) a driver doesn't have to use "#include <linux/i2c.h>" just
>> > > > > > to call to_i2c_client() (or i2c_verify_client()) and (b) you won't do it
>> > > > > > all over again in all sub drivers.
>> > > > > >
>> > > > > > So you could just do a
>> > > > > > regmap = syscon_i2c_to_regmap(pdev->dev.parent);
>> > > > > >
>> > > > > > I've also noticed that the mmio syscon uses device_node as parameter.
>> > > > > > What
>> > > > > > was the reason to divert from that? Just curious.
>> > > > >
>> > > > > How is this supposed to be used?
>> > > > >
>> > > > > I had something like the following in mind:
>> > > > >
>> > > > > &i2c {
>> > > > > cpld@4a {
>> > > > > compatible = "simple-mfd";
>> > > > > reg = <0x4a>;
>> > > > >
>> > > > > gpio@4 {
>> > > > > compatible = "vendor,gpio";
>> > > > > reg = <0x4>;
>> > > > > };
>> > > > > };
>> > > > > };
>> > > >
>> > > > Yes, that was the idea.
>> > > >
>> > > > > But I think the childen are not enumerated if its an I2C device. And
>> > > > > the actual i2c driver is also missing.
>> > > >
>> > > > What do you mean? Can you elaborate?
>> > >
>> > > There is no i2c_driver instance who would create the regmap.
>> >
>> > The regmap is created by the first caller of:
>> >
>> > syscon_i2c_to_regmap{_config}()
>>
>> But which one is an i2c_driver? All the sub devices are platform
>> drivers
>> and there should be no need for them to know that they are behind an
>> i2c driver (or spi driver or just mmio). All they have to know is how
>> to access the registers.
>>
>> > > If I'm
>> > > reading the I2C code correctly, it won't probe any i2c device of a
>> > > bus if there is no i2c_driver with an associated .probe() or
>> > > .probe_new().
>> >
>> > Why wouldn't the children be registered using i2c_driver?
>>
>> Where is the code which enumerates the children?
>
> Yes, I see the problem now. So I2C devices depend on a device
> registering with the i2c_driver framework, which then probes the
> device accordingly. Thus a physical driver is required to convert I2C
> devices to platform devices. So this stops being an MFD problem and
> starts being a 'simple-i2c' issue. :)
Yes, but this is still MFD specifc, because no other normal (in lack of
a better word, think of one-function-devices) I2C device has sub-nodes.
Thus my proposal for that simple-mfd-i2c driver. And keep in mind that
this likely isn't specific to I2C but also to SPI (without having
looked at it). So in theory that simple-mfd-i2c, could also register
a spi_driver which then registers an SPI regmap and enumerates the
children. So this is not only an I2C topic, but IMHO still MFD.
-michael
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next prev parent reply other threads:[~2020-07-02 9:14 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200622075145.1464020-1-lee.jones@linaro.org>
2020-06-30 9:16 ` [PATCH v4 1/1] mfd: Add I2C based System Configuaration (SYSCON) access Michael Walle
2020-06-30 22:32 ` Michael Walle
2020-07-01 7:04 ` Lee Jones
2020-07-01 21:01 ` Michael Walle
2020-07-02 6:54 ` Lee Jones
2020-07-02 7:02 ` Michael Walle
2020-07-02 8:18 ` Lee Jones
2020-07-02 9:12 ` Michael Walle [this message]
2020-07-02 7:14 ` Lee Jones
2020-07-02 7:21 ` Michael Walle
2020-07-05 13:10 ` kernel test robot
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