Re: [PATCH 5/7] mfd: ds90ux9xx: add I2C bridge/alias and link connection driver

Hi Vladimir,

(CC'ing Wolfram)

On Friday, 12 October 2018 10:32:32 EEST Vladimir Zapolskiy wrote:

On 10/12/2018 09:04 AM, Lee Jones wrote:

quoted

On Tue, 09 Oct 2018, Vladimir Zapolskiy wrote:

quoted

From: Vladimir Zapolskiy <redacted>

The change adds TI DS90Ux9xx I2C bridge/alias subdevice driver and
FPD Link connection handling mechanism.

Access to I2C devices connected to a remote de-/serializer is done in
a transparent way, on established link detection event such devices
are registered on an I2C bus, which serves a local de-/serializer IC.

The development of the driver was a collaborative work, the
contribution done by Balasubramani Vivekanandan includes:
* original simplistic implementation of the driver,
* support of implicitly specified devices in device tree,
* support of multiple FPD links for TI DS90Ux9xx,
* other kind of valuable review comments, clean-ups and fixes.

Also Steve Longerbeam made the following changes:
* clear address maps after linked device removal,
* disable pass-through in disconnection,
* qualify locked status with non-zero remote address.

Signed-off-by: Vladimir Zapolskiy <redacted>
---

 drivers/mfd/Kconfig                |   8 +
 drivers/mfd/Makefile               |   1 +
 drivers/mfd/ds90ux9xx-i2c-bridge.c | 764 +++++++++++++++++++++++++++++
 3 files changed, 773 insertions(+)
 create mode 100644 drivers/mfd/ds90ux9xx-i2c-bridge.c

Shouldn't this live in drivers/i2c?

no, the driver is not for an I2C controller of any kind, and the driver does
not register itself in the I2C subsystem by calling i2c_add_adapter() or
i2c_add_numbered_adapter() or i2c_mux_add_adapter() etc, this topic was
discussed with Wolfram also.

(Who is now on CC)

Formally the driver converts the managed IC into a multi-address I2C
slave device, I understand that it does not sound like a well suited driver
for MFD, but ds90ux9xx-core.c and ds90ux9xx-i2c-bridge.c drivers are quite
tightly coupled.

As mentioned in other e-mails in this thread I don't think this should be 
split out to a separate driver, I would move the functionality to the 
ds90ux9xx driver. You may want to register an I2C mux, but as you have a 
single port, that could be overkill. I haven't studied in details how to best 
support this chip using the existing I2C subsystems APIs (which we may want to 
extend if it needed), but I believe that (in your use cases) the deserializer 
should be a child of the serializer, and modeled as an I2C device.

-- 
Regards,

Laurent Pinchart