Re: [PATCH v5 1/3] serdev: handle devices without an ACPI or device tree node

[An Wu]

Hi Markus
    Working on it,
Thank you~

BR
    An

On Sat, Oct 24, 2026 at 8:58 PM Markus Probst <markus.probst@xxxxxxxxx> wrote:
>
> On Sat, 2026-10-24 at 20:04 +0800, ChunAn Wu wrote:
> > Serdev clients instantiated by a driver have no ACPI companion and no
> > device tree node. Their modalias read returns -ENODEV, their add uevent
> > is suppressed, and they cannot be driver-matched, so creators force a
> > bind with device_driver_attach().
> >
> > Resolve both TODOs in the serdev core by modelling matching on the SPI
> > bus: let the creator pass a modalias to serdev_device_add() and give
> > struct serdev_device_driver an id_table. ACPI and OF are still tried
> > first; clients without their own modalias keep returning -ENODEV. The
> > device name, derived from the controller, is unchanged.
> >
> > Split struct serdev_device_id and its defines into a new
> > include/linux/device-id/serdev.h, following the pattern already used by
> > the SPI and I2C buses.
> >
> > Signed-off-by: ChunAn Wu <an.wu@xxxxxxxxxxxxx>
> > ---
> >  MAINTAINERS                                   |  1 +
> >  .../platform/x86/x86-android-tablets/core.c   |  2 +-
> >  drivers/power/sequencing/pwrseq-pcie-m2.c     |  2 +-
> >  drivers/tty/serdev/core.c                     | 62 ++++++++++++++++---
> >  include/linux/device-id/serdev.h              | 19 ++++++
> >  include/linux/serdev.h                        | 12 +++-
> >  6 files changed, 86 insertions(+), 12 deletions(-)
> >  create mode 100644 include/linux/device-id/serdev.h
> >
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 917f3f72e31b..06e67aa5d9b0 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -24905,6 +24905,7 @@ L:    linux-serial@xxxxxxxxxxxxxxx
> >  S:   Maintained
> >  F:   Documentation/devicetree/bindings/serial/serial.yaml
> >  F:   drivers/tty/serdev/
> > +F:   include/linux/device-id/serdev.h
> >  F:   include/linux/serdev.h
> >  F:   rust/helpers/serdev.c
> >  F:   rust/kernel/serdev.rs
> > diff --git a/drivers/platform/x86/x86-android-tablets/core.c b/drivers/platform/x86/x86-android-tablets/core.c
> > index cfff7f5eac5d..853aa6ff5d50 100644
> > --- a/drivers/platform/x86/x86-android-tablets/core.c
> > +++ b/drivers/platform/x86/x86-android-tablets/core.c
> > @@ -317,7 +317,7 @@ static __init int x86_instantiate_serdev(const struct x86_dev_info *dev_info, in
> >       ACPI_COMPANION_SET(&serdev->dev, serdev_adev);
> >       acpi_device_set_enumerated(serdev_adev);
> >
> > -     ret = serdev_device_add(serdev);
> > +     ret = serdev_device_add(serdev, NULL);
> >       if (ret) {
> >               dev_err(&serdev->dev, "error %d adding serdev\n", ret);
> >               serdev_device_put(serdev);
> > diff --git a/drivers/power/sequencing/pwrseq-pcie-m2.c b/drivers/power/sequencing/pwrseq-pcie-m2.c
> > index e42e85f47629..e0482f2ef39f 100644
> > --- a/drivers/power/sequencing/pwrseq-pcie-m2.c
> > +++ b/drivers/power/sequencing/pwrseq-pcie-m2.c
> > @@ -309,7 +309,7 @@ static int pwrseq_pcie_m2_create_serdev_one(struct pwrseq_pcie_m2_ctx *ctx,
> >       if (ret)
> >               goto err_free_serdev;
> >
> > -     ret = serdev_device_add(pci_dev->serdev);
> > +     ret = serdev_device_add(pci_dev->serdev, NULL);
> >       if (ret) {
> >               dev_err(dev, "Failed to add serdev for PCI device (%s): %d\n",
> >                       pci_name(pdev), ret);
> > diff --git a/drivers/tty/serdev/core.c b/drivers/tty/serdev/core.c
> > index 7500efcdfc21..e0517d5a48da 100644
> > --- a/drivers/tty/serdev/core.c
> > +++ b/drivers/tty/serdev/core.c
> > @@ -29,13 +29,21 @@ static DEFINE_IDA(ctrl_ida);
> >  static ssize_t modalias_show(struct device *dev,
> >                            struct device_attribute *attr, char *buf)
> >  {
> > +     const struct serdev_device *serdev = to_serdev_device(dev);
> >       int len;
> >
> >       len = acpi_device_modalias(dev, buf, PAGE_SIZE - 1);
> >       if (len != -ENODEV)
> >               return len;
> >
> > -     return of_device_modalias(dev, buf, PAGE_SIZE);
> > +     len = of_device_modalias(dev, buf, PAGE_SIZE);
> > +     if (len != -ENODEV)
> > +             return len;
> > +
> > +     if (!serdev->modalias[0])
> > +             return -ENODEV;
> > +
> > +     return sysfs_emit(buf, "%s%s\n", SERDEV_MODULE_PREFIX, serdev->modalias);
> >  }
> >  static DEVICE_ATTR_RO(modalias);
> >
> > @@ -47,15 +55,22 @@ ATTRIBUTE_GROUPS(serdev_device);
> >
> >  static int serdev_device_uevent(const struct device *dev, struct kobj_uevent_env *env)
> >  {
> > +     const struct serdev_device *serdev = to_serdev_device(dev);
> >       int rc;
> >
> > -     /* TODO: platform modalias */
> > -
> >       rc = acpi_device_uevent_modalias(dev, env);
> >       if (rc != -ENODEV)
> >               return rc;
> >
> > -     return of_device_uevent_modalias(dev, env);
> > +     rc = of_device_uevent_modalias(dev, env);
> > +     if (rc != -ENODEV)
> > +             return rc;
> > +
> > +     if (!serdev->modalias[0])
> > +             return -ENODEV;
> > +
> > +     return add_uevent_var(env, "MODALIAS=%s%s", SERDEV_MODULE_PREFIX,
> > +                           serdev->modalias);
> >  }
> >
> >  static void serdev_device_release(struct device *dev)
> > @@ -86,28 +101,57 @@ static const struct device_type serdev_ctrl_type = {
> >       .release        = serdev_ctrl_release,
> >  };
> >
> > +static const struct serdev_device_id *serdev_match_id(const struct serdev_device_id *id,
> > +                                                   const char *modalias)
> > +{
> > +     if (!id || !modalias[0])
> > +             return NULL;
> > +
> > +     while (id->name[0]) {
> > +             if (!strcmp(modalias, id->name))
> > +                     return id;
> > +             id++;
> > +     }
> > +
> > +     return NULL;
> > +}
> > +
> >  static int serdev_device_match(struct device *dev, const struct device_driver *drv)
> >  {
> > +     const struct serdev_device *serdev;
> > +     const struct serdev_device_driver *sdrv;
> > +
> >       if (!is_serdev_device(dev))
> >               return 0;
> >
> > -     /* TODO: platform matching */
> > +     serdev = to_serdev_device(dev);
> > +     sdrv = to_serdev_device_driver(drv);
> > +
> >       if (acpi_driver_match_device(dev, drv))
> >               return 1;
> >
> > -     return of_driver_match_device(dev, drv);
> > +     if (of_driver_match_device(dev, drv))
> > +             return 1;
> > +
> > +     return !!serdev_match_id(sdrv->id_table, serdev->modalias);
> >  }
> >
> >  /**
> >   * serdev_device_add() - add a device previously constructed via serdev_device_alloc()
> >   * @serdev:  serdev_device to be added
> > + * @modalias:        Driver name or alias, used to match devices which have neither
> > + *           an ACPI companion nor a device tree node. NULL for devices
> > + *           enumerated from firmware.
> >   */
> > -int serdev_device_add(struct serdev_device *serdev)
> > +int serdev_device_add(struct serdev_device *serdev, const char *modalias)
> >  {
> >       struct serdev_controller *ctrl = serdev->ctrl;
> >       struct device *parent = serdev->dev.parent;
> >       int err;
> >
> > +     if (modalias)
> > +             strscpy(serdev->modalias, modalias);
> > +
> >       dev_set_name(&serdev->dev, "%s-%d", dev_name(parent), serdev->nr);
> >
> >       /* Only a single slave device is currently supported. */
> > @@ -553,7 +597,7 @@ static int of_serdev_register_devices(struct serdev_controller *ctrl)
> >
> >               device_set_node(&serdev->dev, of_fwnode_handle(node));
> >
> > -             err = serdev_device_add(serdev);
> > +             err = serdev_device_add(serdev, NULL);
> >               if (err) {
> >                       dev_err(&serdev->dev,
> >                               "failure adding device. status %pe\n",
> > @@ -707,7 +751,7 @@ static acpi_status acpi_serdev_register_device(struct serdev_controller *ctrl,
> >       ACPI_COMPANION_SET(&serdev->dev, adev);
> >       acpi_device_set_enumerated(adev);
> >
> > -     err = serdev_device_add(serdev);
> > +     err = serdev_device_add(serdev, NULL);
> >       if (err) {
> >               dev_err(&serdev->dev,
> >                       "failure adding ACPI serdev device. status %pe\n",
> > diff --git a/include/linux/device-id/serdev.h b/include/linux/device-id/serdev.h
> > new file mode 100644
> > index 000000000000..96644953cece
> > --- /dev/null
> > +++ b/include/linux/device-id/serdev.h
> > @@ -0,0 +1,19 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#ifndef LINUX_DEVICE_ID_SERDEV_H
> > +#define LINUX_DEVICE_ID_SERDEV_H
> > +
> > +#ifdef __KERNEL__
> > +typedef unsigned long kernel_ulong_t;
> > +#endif
> > +
> > +/* serdev */
> > +
> > +#define SERDEV_NAME_SIZE     40
> > +#define SERDEV_MODULE_PREFIX "serial:"
> > +
> > +struct serdev_device_id {
> > +     char name[SERDEV_NAME_SIZE];
> > +     kernel_ulong_t driver_data;     /* Data private to the driver */
> > +};
> > +
> > +#endif /* ifndef LINUX_DEVICE_ID_SERDEV_H */
> > diff --git a/include/linux/serdev.h b/include/linux/serdev.h
> > index b6c3d957ec15..96a441abc1ac 100644
> > --- a/include/linux/serdev.h
> > +++ b/include/linux/serdev.h
> > @@ -7,7 +7,9 @@
> >
> >  #include <linux/types.h>
> >  #include <linux/device.h>
> > +#include <linux/device-id/serdev.h>
> >  #include <linux/iopoll.h>
> > +#include <linux/string.h>
> Unused include.
>
> >  #include <linux/uaccess.h>
> >  #include <linux/termios.h>
> >  #include <linux/delay.h>
> > @@ -35,6 +37,10 @@ struct serdev_device_ops {
> >   * struct serdev_device - Basic representation of an serdev device
> >   * @dev:     Driver model representation of the device.
> >   * @nr:              Device number on serdev bus.
> > + * @modalias:        Name of the driver to use with this device, or the alias
> > + *           for it. Empty for devices enumerated from firmware, which
> > + *           are identified through their ACPI companion or their device
> > + *           tree node instead. See serdev_device_add().
> >   * @ctrl:    serdev controller managing this device.
> >   * @ops:     Device operations.
> >   * @write_comp:      Completion used by serdev_device_write() internally
> > @@ -43,6 +49,7 @@ struct serdev_device_ops {
> >  struct serdev_device {
> >       struct device dev;
> >       int nr;
> > +     char modalias[SERDEV_NAME_SIZE];
> >       struct serdev_controller *ctrl;
> >       const struct serdev_device_ops *ops;
> >       struct completion write_comp;
> > @@ -55,12 +62,15 @@ struct serdev_device {
> >   * struct serdev_device_driver - serdev slave device driver
> >   * @driver:  serdev device drivers should initialize name field of this
> >   *           structure.
> > + * @id_table:        List of serdev devices supported by this driver, used to
> > + *           match devices which are not enumerated from firmware.
> >   * @probe:   binds this driver to a serdev device.
> >   * @remove:  unbinds this driver from the serdev device.
> >   * @shutdown:        shut down this serdev device.
> >   */
> >  struct serdev_device_driver {
> >       struct device_driver driver;
> > +     const struct serdev_device_id *id_table;
> >       int     (*probe)(struct serdev_device *);
> >       void    (*remove)(struct serdev_device *);
> >       void    (*shutdown)(struct serdev_device *);
> > @@ -158,7 +168,7 @@ static inline void serdev_controller_put(struct serdev_controller *ctrl)
> >  }
> >
> >  struct serdev_device *serdev_device_alloc(struct serdev_controller *);
> > -int serdev_device_add(struct serdev_device *);
> > +int serdev_device_add(struct serdev_device *serdev, const char *modalias);
> >  void serdev_device_remove(struct serdev_device *);
> >
> >  struct serdev_controller *serdev_controller_alloc(struct device *host,
>
> You will need to address the sashiko report (both are true positives).
>
> In the scripts/mod/file2alias.c file, you can copy the spi entry.
> scripts/mod/devicetable-offsets.{h,c,s} and
> include/linux/mod_devicetable.h are also relevant for this.
> (Didn't know myself those files existed, so thx Sashiko)
>
> Also add serdev_device_id to scripts/coccinelle/misc/of_table.cocci .
>
>
> With that fixed,
>
> Reviewed-by: Markus Probst <markus.probst@xxxxxxxxx>
>
>
> Thanks
> - Markus Probst