linux-kernel - Re: [PATCH v2 02/10] serdev: Add serdev device based driver match support

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Message-ID: <CAMRc=MdNTHtzTJ3f3qVHH=qFbK86MzUP0vvx3ogZsXG+iqMUnw@mail.gmail.com>
Date: Fri, 2 Jan 2026 12:13:27 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Manivannan Sadhasivam <mani@...nel.org>
Cc: manivannan.sadhasivam@....qualcomm.com, 
	Manivannan Sadhasivam via B4 Relay <devnull+manivannan.sadhasivam.oss.qualcomm.com@...nel.org>, 
	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>, Rob Herring <robh@...nel.org>, 
	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>
Subject: Re: [PATCH v2 02/10] serdev: Add serdev device based driver match support

On Tue, Dec 30, 2025 at 8:56 AM Manivannan Sadhasivam <mani@...nel.org> wrote:
>
> On Thu, Nov 27, 2025 at 06:32:04AM -0800, Bartosz Golaszewski wrote:
> > On Tue, 25 Nov 2025 15:45:06 +0100, Manivannan Sadhasivam via B4 Relay
> > <devnull+manivannan.sadhasivam.oss.qualcomm.com@...nel.org> said:
> > > From: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
> > >
> > > Add support to match serdev devices with serdev drivers based on the serdev
> > > ID table defined in serdev_device_driver::id_table.
> > >
> > > The matching function, serdev_driver_match_device() uses the serdev device
> > > name to match against the entries in serdev_device_driver::id_table.
> > >
> > > If there is no serdev id_table for the driver, then serdev_device_match()
> > > will fallback to ACPI and DT based matching.
> > >
> > > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
> > > ---
> > >  drivers/tty/serdev/core.c         | 23 ++++++++++++++++++++++-
> > >  include/linux/mod_devicetable.h   |  7 +++++++
> > >  include/linux/serdev.h            |  4 ++++
> > >  scripts/mod/devicetable-offsets.c |  3 +++
> > >  4 files changed, 36 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/tty/serdev/core.c b/drivers/tty/serdev/core.c
> > > index b33e708cb245..2b5582cd5063 100644
> > > --- a/drivers/tty/serdev/core.c
> > > +++ b/drivers/tty/serdev/core.c
> > > @@ -85,12 +85,33 @@ static const struct device_type serdev_ctrl_type = {
> > >     .release        = serdev_ctrl_release,
> > >  };
> > >
> > > +static int serdev_driver_match_device(struct device *dev, const struct device_driver *drv)
> > > +{
> > > +   const struct serdev_device_driver *serdev_drv = to_serdev_device_driver(drv);
> > > +   struct serdev_device *serdev = to_serdev_device(dev);
> > > +   const struct serdev_device_id *id;
> > > +
> > > +   if (!serdev_drv->id_table)
> > > +           return 0;
> > > +
> > > +   for (id = serdev_drv->id_table; id->name[0]; id++) {
> > > +           if (!strcmp(dev_name(dev), id->name)) {
> > > +                   serdev->id = id;
> > > +                   return 1;
> > > +           }
> > > +   }
> > > +
> > > +   return 0;
> > > +}
> > > +
> >
> > I don't know if Rob agrees with me but I would very much prefer to see
> > software-node-based approach instead of an ID table matching.
> >
> > Could you in the pwrseq driver, create a software node for the serdev device
> > you allocate, set its "compatible" to "qcom,wcn7850-bt" and match against it
> > here?
> >
> > This has several benefits: if you ever need to pass more properties to the
> > serdev devices, you already have a medium for that and you can also leave
> > serdev_device_add() alone. You're comparing the entire name here - what if
> > someone sets device's ID to some value and the name will be "WCN7850.2"?
> >
> > You could also drop the serdev_id field from struct serdev_device. For matching
> > you could even reuse the of_device_id from the device driver.
> >
>
> I tried this approach and I really liked it since it gets rid of the yet-another
> id_table for serdev (which I didn't like it btw). But there is one concern
> though. We need a generic 'device_get_match_data' implementation for swnode.
> While trying to implement it, I stumbled upon this patch [1] which does the same
> for other usecase, but there was a disagreement on whether swnode should be used
> for driver matching or not. For my usecase, I find it very useful and
> reasonable, but Dmitry Torokhov believes otherwise.
>
> Maybe I'll include this patch in the next version, CC Dmitry and see where it
> goes.

Thanks for bringing this to my attention. I think that historically
software nodes were meant to always be "secondary" but now we have all
kinds of auxiliary devices that use software nodes as their "primary"
nodes so maybe we can re-discuss this.

Bart