Re: [PATCH v4 2/2] phy: qcom-mipi-csi2: Add a CSI2 MIPI DPHY driver

[Vladimir Zapolskiy]

On 3/19/26 17:18, Bryan O'Donoghue wrote:
> On 19/03/2026 14:56, Vladimir Zapolskiy wrote:
> > > There's no reason to remove that from CAMSS - it would be an ABI break
> > > in user-space anyway.
> >
> > If technically CAMSS CSIPHY could be excluded from the list of CAMSS media
> > subdevices, then for the sake of simplification it should be done for all
> > supported platforms in advance, such a change will be independent from this
> > particular phy series, and vice versa, this CAMSS only driver change will
> > prepare a ground for media-less CAMSS CSIPHY device drivers, hence it shall
> > precede this particular CAMSS CSIPHY series.
> >
> > For backward compatibility with userspace a noop stub will be good enough,
> > it's not an issue at all.
>
> The standalone PHY driver doesn't require removing the CSIPHY media
> entity from CAMSS. They serve different purposes and coexist - its
> important to have a NOP from user-space perspective for legacy and
> indeed for new implementations.

There should be no two CAMSS CSIPHY device (or subdevice) drivers, where
one chop of CAMSS CSIPHY device driver remains to sit under media, and
another one is under phy subsystem, since it's a further degradation from
the current already pretty awful state of the CAMSS driver, but at least
CSIPHY is not scattered over different subsystems today.

It might be fine to move device driver parts related to CAMSS CSIPHY
driver from media subsystem to phy subsystem, however if only a partial
transition is planned, and CSIPHY device support is split into two device
(sub-)drivers, then it merely exposes a quite severe design flaw.

It looks like it's still undecided, if CAMSS CSIPHY IP is a phy or media
device, it can not be both at the same time.

> How the PHY gets represented in the kernel is of zero interest to
> user-sapce.
>
> That said, stubbing out the media entity is independent work that can
> happen in any order and IMO is a separate debate. Whether or not CSIPHY
> init sequences live inside of a monolithic CAMSS driver or live inside
> off a discrete csiphy driver is not related to the media graph.
>
> Happy to have that debate - and if indicated, carefully apply patches
> separately.

--
Best wishes,
Vladimir