[PATCH 00/17] i2c: deprecate class based instantiation for embedded I2C drivers

[Wolfram Sang]

With I2C, class based instantiation means if a master driver has e.g.
I2C_CLASS_HWMON set, all slave drivers with this class will try to probe a
device using an array of possible addresses and some heuristics. That creates
traffic and needs time, even when nothing is connected. This mechanism is
needed when you do not have another method to describe the slaves. Embedded I2C
drivers do not need class based instantiation, since there is i2c_board_info or
devicetree description. Some drivers have the class flags set, though, and it
has spread further over the years. We can't remove the flags directly, because
there might be users out there relying on this feature. So, we add a
deprecation warning if a device is instantiated via class attributes. After
giving some time to switch over, we can then finally remove the class flags and
gain boot time.

Patch 1 adds some missing documentation. Patch 2 adds the deprecation feature.
Patches 3+4 are tested on hardware I need. Patches 5-17 are suggestions for
drivers I think could benefit from that. For those, acks are needed before I
will apply them to my tree. If you use a different driver which can also
benefit from this, just send a patch adding the new DEPRECATED flag.

The series can also be found here:

git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux.git i2c/deprecated_class

Thanks,

Wolfram


Wolfram Sang (17):
Documentation: i2c: describe devicetree method for instantiating
devices
i2c: add deprecation warning for class based instantiation
i2c: i2c-omap: deprecate class based instantiation
i2c: i2c-at91: deprecate class based instantiation
i2c: i2c-bcm2835: deprecate class based instantiation
i2c: i2c-bfin-twi: deprecate class based instantiation
i2c: i2c-davinci: deprecate class based instantiation
i2c: i2c-designware-platdrv: deprecate class based instantiation
i2c: i2c-mv64xxx: deprecate class based instantiation
i2c: i2c-nomadik: deprecate class based instantiation
i2c: i2c-ocores: deprecate class based instantiation
i2c: i2c-rcar: deprecate class based instantiation
i2c: i2c-s3c2410: deprecate class based instantiation
i2c: i2c-sirf: deprecate class based instantiation
i2c: i2c-stu300: deprecate class based instantiation
i2c: i2c-tegra: deprecate class based instantiation
i2c: i2c-xiic: deprecate class based instantiation

Documentation/i2c/instantiating-devices | 34 +++++++++++++++++++++++++++--
drivers/i2c/busses/i2c-at91.c | 2 +-
drivers/i2c/busses/i2c-bcm2835.c | 2 +-
drivers/i2c/busses/i2c-bfin-twi.c | 2 +-
drivers/i2c/busses/i2c-davinci.c | 2 +-
drivers/i2c/busses/i2c-designware-platdrv.c | 2 +-
drivers/i2c/busses/i2c-mv64xxx.c | 2 +-
drivers/i2c/busses/i2c-nomadik.c | 2 +-
drivers/i2c/busses/i2c-ocores.c | 2 +-
drivers/i2c/busses/i2c-omap.c | 2 +-
drivers/i2c/busses/i2c-rcar.c | 2 +-
drivers/i2c/busses/i2c-s3c2410.c | 2 +-
drivers/i2c/busses/i2c-sirf.c | 2 +-
drivers/i2c/busses/i2c-stu300.c | 2 +-
drivers/i2c/busses/i2c-tegra.c | 2 +-
drivers/i2c/busses/i2c-xiic.c | 2 +-
drivers/i2c/i2c-core.c | 7 ++++++
include/linux/i2c.h | 1 +
18 files changed, 55 insertions(+), 17 deletions(-)

[Wolfram Sang]

Warn users that class based instantiation is going away soon in favour
of more robust probing and faster bootup times.

Signed-off-by: Wolfram Sang <wsa at the-dreams.de>
Cc: Sekhar Nori <nsekhar at ti.com>
Cc: Kevin Hilman <khilman at deeprootsystems.com>
---

This patch is a suggestion. Looking for an ack by someone who actually uses
the driver.

drivers/i2c/busses/i2c-davinci.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/i2c/busses/i2c-davinci.c b/drivers/i2c/busses/i2c-davinci.c
index af0b583..389bc68 100644
--- a/drivers/i2c/busses/i2c-davinci.c
+++ b/drivers/i2c/busses/i2c-davinci.c
@@ -712,7 +712,7 @@ static int davinci_i2c_probe(struct platform_device *pdev)
adap = &dev->adapter;
i2c_set_adapdata(adap, dev);
adap->owner = THIS_MODULE;
- adap->class = I2C_CLASS_HWMON;
+ adap->class = I2C_CLASS_HWMON | I2C_CLASS_DEPRECATED;
strlcpy(adap->name, "DaVinci I2C adapter", sizeof(adap->name));
adap->algo = &i2c_davinci_algo;
adap->dev.parent = &pdev->dev;

[Wolfram Sang]

Post by Wolfram Sang
With I2C, class based instantiation means if a master driver has e.g.
I2C_CLASS_HWMON set, all slave drivers with this class will try to probe a
device using an array of possible addresses and some heuristics. That creates
traffic and needs time, even when nothing is connected. This mechanism is
needed when you do not have another method to describe the slaves. Embedded I2C
drivers do not need class based instantiation, since there is i2c_board_info or
devicetree description. Some drivers have the class flags set, though, and it
has spread further over the years. We can't remove the flags directly, because
there might be users out there relying on this feature. So, we add a
deprecation warning if a device is instantiated via class attributes. After
giving some time to switch over, we can then finally remove the class flags and
gain boot time.
Patch 1 adds some missing documentation. Patch 2 adds the deprecation feature.
Patches 3+4 are tested on hardware I need. Patches 5-17 are suggestions for
drivers I think could benefit from that. For those, acks are needed before I
will apply them to my tree. If you use a different driver which can also
benefit from this, just send a patch adding the new DEPRECATED flag.
git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux.git i2c/deprecated_class
Thanks,
Wolfram
Documentation: i2c: describe devicetree method for instantiating
devices
i2c: add deprecation warning for class based instantiation
i2c: i2c-omap: deprecate class based instantiation
i2c: i2c-at91: deprecate class based instantiation
i2c: i2c-bcm2835: deprecate class based instantiation
i2c: i2c-bfin-twi: deprecate class based instantiation
i2c: i2c-davinci: deprecate class based instantiation
i2c: i2c-designware-platdrv: deprecate class based instantiation
i2c: i2c-mv64xxx: deprecate class based instantiation
i2c: i2c-nomadik: deprecate class based instantiation
i2c: i2c-ocores: deprecate class based instantiation
i2c: i2c-rcar: deprecate class based instantiation
i2c: i2c-s3c2410: deprecate class based instantiation
i2c: i2c-sirf: deprecate class based instantiation
i2c: i2c-stu300: deprecate class based instantiation
i2c: i2c-tegra: deprecate class based instantiation
i2c: i2c-xiic: deprecate class based instantiation

I reconsidered and have now applied all patches. That way, all these
drivers can be converted to no class based instantiation in one go after
some grace period. If it turns out, one driver actually needs it, there
is still the grace period left to remove the DEPRECATED flag again.

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