Re: [PATCH v3 0/5] phy: core: rework phy_set_mode to accept phy mode and submode

Hi Grygorii, Kishon,

On Mon, Nov 19, 2018 at 07:24:19PM -0600, Grygorii Strashko wrote:

Thank you for your review.
I've not added "Tested-by"/"Acked-by" tags due to code changes in v3.

As was discussed in [1] I'm posting series which introduces rework of
phy_set_mode to accept phy mode and submode. I've dropped TI specific patches as
this change is pretty big by itself.

Patch 1 is cumulative change which refactors PHY framework code to
support dual level PHYs mode configuration - PHY mode and PHY submode. It
extends .set_mode() callback to support additional parameter "int submode"
and converts all corresponding PHY drivers to support new .set_mode()
callback declaration.
The new extended PHY API
 int phy_set_mode_ext(struct phy *phy, enum phy_mode mode, int submode)
is introduced to support dual level PHYs mode configuration and existing
phy_set_mode() API is converted to macros, so PHY framework consumers do
not need to be changed (~21 matches).

Patches 2-4: Add new PHY's mode to be used by Ethernet PHY interface drivers or
multipurpose PHYs like serdes and convert ocelot-serdes and mvebu-cp110-comphy
PHY drivers to use recently introduced PHY_MODE_ETHERNET and phy_set_mode_ext().

Patch 5 - removes unused, ethernet specific phy modes from enum phy_mode.

Testing:
 - series tested on TI am335x/am437x/am5(dra7) paltforms.
 - other driver build tested.

I realise I'm a bit late to the party, but while working on the D-PHY
support, I noticed a few things that could be improved.

I guess the main issue is that the sub-mode is completely opaque to
the generic phy framework now. This might not be a big issue, and I
assume that it has been done that way because the net framework
already has a define for the submode it wants.

However, this creates a bunch of drawbacks at the phy framework level:

 - phy_set_mode will now pass a submode of 0, all the time. This means
   that the behaviour is undefined for all the modes not using the
   submodes at the moment, and phy_interface_t seems to have the value
   PHY_INTERFACE_MODE_NA matching 0, but I guess this could change in
   the future (or the guarantee is not documented anywhere).
 - on a similar note, there's no documentation for which value to pass
   to phy_set_mode_ext when used with something else than a
   PHY_MODE_ETHERNET.
 - at the provider level, if you're supporting a phy that isn't using
   the submodes, you have no way to filter out or reject any subnode,
   since you have no idea what the "no submode" value is.

I guess this can be addressed by:

A) defining a generic phy framework wide unused / invalid phy submode,
that wouldn't collide with the subnode values (such as -1?), and
making phy_set_mode_ext use that.

B) moving the phy submodes definition to the generic phy headers. This
would allow to have a documented, obvious link between a mode and its
subnodes, for all the actors involved (consumer, provider, and
framework) without prior knowledge.

C) Document what the submodes expectations are

What do you think?
Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com