linux-kernel - Re: [PATCH 6/9] serdev: Skip registering serdev devices from DT is external connector is used

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Message-ID: <cjtnoqjr3v5o64caa6unllb2e2csyvybr6vnzwuqqrl453bgz7@drqmfkfbn5xg>
Date: Wed, 19 Nov 2025 19:02:51 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Rob Herring <robh@...nel.org>
Cc: manivannan.sadhasivam@....qualcomm.com, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Jiri Slaby <jirislaby@...nel.org>, 
	Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas.schier@...ux.dev>, 
	Hans de Goede <hansg@...nel.org>, Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>, 
	Mark Pearson <mpearson-lenovo@...ebb.ca>, "Derek J. Clark" <derekjohn.clark@...il.com>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Marcel Holtmann <marcel@...tmann.org>, Luiz Augusto von Dentz <luiz.dentz@...il.com>, 
	Bartosz Golaszewski <brgl@...ev.pl>, linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-kbuild@...r.kernel.org, platform-driver-x86@...r.kernel.org, linux-pci@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-arm-msm@...r.kernel.org, linux-bluetooth@...r.kernel.org, 
	linux-pm@...r.kernel.org, Stephan Gerhold <stephan.gerhold@...aro.org>, 
	Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Subject: Re: [PATCH 6/9] serdev: Skip registering serdev devices from DT is
 external connector is used

On Tue, Nov 18, 2025 at 07:03:51AM -0600, Rob Herring wrote:
> On Wed, Nov 12, 2025 at 8:45 AM Manivannan Sadhasivam via B4 Relay
> <devnull+manivannan.sadhasivam.oss.qualcomm.com@...nel.org> wrote:
> >
> > From: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
> >
> > If an external connector like M.2 is connected to the serdev controller
> > in DT, then the serdev devices will be created dynamically by the connector
> > driver. So skip registering devices from DT node as there will be no
> > statically defined devices.
> 
> You could still have statically defined devices. You are just choosing
> to probe them later from the connector driver.
> 

The point of coming up with the M.2 binding is to avoid hardcoding the devices
in DT. So static devices are ruled out IMO.

> >
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
> > ---
> >  drivers/tty/serdev/core.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> >
> > diff --git a/drivers/tty/serdev/core.c b/drivers/tty/serdev/core.c
> > index 8c2a40a537d93f4b9353a2f128cdf51b521929b1..1378587d386356ca4415fa455b2ee722b5e44d3e 100644
> > --- a/drivers/tty/serdev/core.c
> > +++ b/drivers/tty/serdev/core.c
> > @@ -12,6 +12,7 @@
> >  #include <linux/kernel.h>
> >  #include <linux/module.h>
> >  #include <linux/of.h>
> > +#include <linux/of_graph.h>
> >  #include <linux/of_device.h>
> >  #include <linux/pm_domain.h>
> >  #include <linux/pm_runtime.h>
> > @@ -560,6 +561,15 @@ static int of_serdev_register_devices(struct serdev_controller *ctrl)
> >         int err;
> >         bool found = false;
> >
> > +       /*
> > +        * When the serdev controller is connected to an external connector like
> > +        * M.2 in DT, then the serdev devices will be created dynamically by the
> > +        * connector driver. So skip looking for devices in DT node as there will
> > +        * be no statically defined devices.
> > +        */
> > +       if (of_graph_is_present(ctrl->dev.of_node))
> > +               return 0;
> 
> Where's the schema that allows graph nodes?
> 

Err... I missed updating it. Will do it in v2.

- Mani

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