[PATCH v2 0/8] drivers: Transition to the faux device interface

[PATCH v2 0/8] drivers: Transition to the faux device interface

[Sudeep Holla]

Recently when debugging why one of the scmi platform device was not
showing up under /sys/devices/platform/firmware:scmi instead was
appearing directly under /sys/devices/platform, I noticed the new
faux interface /sys/devices/faux.

Looking through the discussion and the background, I got excited and
took the opportunity to clear all the platform devices under
/sys/devices/platform on the Arm Juno/FVP platforms that are really
faux devices. Only the platform devices created for the device nodes
from the DT remain under /sys/devices/platform after these changes.

All the patches are independent of each other and are part of the series
just to demonstrate the use of macro module_faux_driver() where
applicable. The idea is to get the macro merged first and then push the
individual patches via respective subsystem later.

Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
---
Changes in v2:
- Dropped all the modalias expect efivars(reason in the patch)
- Defined new helper macro module_faux_driver() and moved most of the
  drivers to use it
- Dropped already queued ASoC and regulator changes
- Link to v1: https://lore.kernel.org/r/20250317-plat2faux_dev-v1-0-5fe67c085ad5@arm.com

---
Sudeep Holla (8):
      driver core: add helper macro for module_faux_driver() boilerplate
      cpuidle: psci: Transition to the faux device interface
      hwrng: arm-smccc-trng - transition to the faux device interface
      rtc: efi: Transition to the faux device interface
      virt: efi_secret: Transition to the faux device interface
      efi: efivars: Transition to the faux device interface
      ACPI: APEI: EINJ: Transition to the faux device interface
      net: phy: fixed_phy: transition to the faux device interface

 drivers/acpi/apei/einj-core.c             | 51 ++++---------------------------
 drivers/char/hw_random/arm_smccc_trng.c   | 19 +++++-------
 drivers/cpuidle/cpuidle-psci.c            | 32 +++----------------
 drivers/firmware/efi/efi-pstore.c         |  2 +-
 drivers/firmware/efi/efi.c                | 12 ++------
 drivers/firmware/smccc/smccc.c            | 17 -----------
 drivers/net/phy/fixed_phy.c               | 16 +++++-----
 drivers/rtc/rtc-efi.c                     | 16 +++-------
 drivers/virt/coco/efi_secret/efi_secret.c | 29 +++++-------------
 include/linux/device/faux.h               | 49 +++++++++++++++++++++++++++++
 10 files changed, 90 insertions(+), 153 deletions(-)
---
base-commit: 4701f33a10702d5fc577c32434eb62adde0a1ae1
change-id: 20250315-plat2faux_dev-8c28b35be96a
-- 
Regards,
Sudeep

[PATCH v2 8/8] net: phy: fixed_phy: transition to the faux device interface

[Sudeep Holla]

The net fixed phy driver does not require the creation of a platform
device. Originally, this approach was chosen for simplicity when the
driver was first implemented.

With the introduction of the lightweight faux device interface, we now
have a more appropriate alternative. Migrate the device to utilize the
faux bus, given that the platform device it previously created was not
a real one anyway. This will get rid of the fake platform device.

Cc: Andrew Lunn <andrew@lunn.ch>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: netdev@vger.kernel.org
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
---
 drivers/net/phy/fixed_phy.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/net/phy/fixed_phy.c b/drivers/net/phy/fixed_phy.c
index aef739c20ac4d5a271465a677a85ef7c18cfce70..ee7831a9849b3728ca9c541da35d17e089985da2 100644
--- a/drivers/net/phy/fixed_phy.c
+++ b/drivers/net/phy/fixed_phy.c
@@ -10,7 +10,7 @@
 
 #include <linux/kernel.h>
 #include <linux/module.h>
-#include <linux/platform_device.h>
+#include <linux/device/faux.h>
 #include <linux/list.h>
 #include <linux/mii.h>
 #include <linux/phy.h>
@@ -40,7 +40,7 @@ struct fixed_phy {
 	struct gpio_desc *link_gpiod;
 };
 
-static struct platform_device *pdev;
+static struct faux_device *fdev;
 static struct fixed_mdio_bus platform_fmb = {
 	.phys = LIST_HEAD_INIT(platform_fmb.phys),
 };
@@ -337,9 +337,9 @@ static int __init fixed_mdio_bus_init(void)
 	struct fixed_mdio_bus *fmb = &platform_fmb;
 	int ret;
 
-	pdev = platform_device_register_simple("Fixed MDIO bus", 0, NULL, 0);
-	if (IS_ERR(pdev))
-		return PTR_ERR(pdev);
+	fdev = faux_device_create("Fixed MDIO bus", NULL, NULL);
+	if (!fdev)
+		return -ENODEV;
 
 	fmb->mii_bus = mdiobus_alloc();
 	if (fmb->mii_bus == NULL) {
@@ -350,7 +350,7 @@ static int __init fixed_mdio_bus_init(void)
 	snprintf(fmb->mii_bus->id, MII_BUS_ID_SIZE, "fixed-0");
 	fmb->mii_bus->name = "Fixed MDIO Bus";
 	fmb->mii_bus->priv = fmb;
-	fmb->mii_bus->parent = &pdev->dev;
+	fmb->mii_bus->parent = &fdev->dev;
 	fmb->mii_bus->read = &fixed_mdio_read;
 	fmb->mii_bus->write = &fixed_mdio_write;
 	fmb->mii_bus->phy_mask = ~0;
@@ -364,7 +364,7 @@ static int __init fixed_mdio_bus_init(void)
 err_mdiobus_alloc:
 	mdiobus_free(fmb->mii_bus);
 err_mdiobus_reg:
-	platform_device_unregister(pdev);
+	faux_device_destroy(fdev);
 	return ret;
 }
 module_init(fixed_mdio_bus_init);
@@ -376,7 +376,7 @@ static void __exit fixed_mdio_bus_exit(void)
 
 	mdiobus_unregister(fmb->mii_bus);
 	mdiobus_free(fmb->mii_bus);
-	platform_device_unregister(pdev);
+	faux_device_destroy(fdev);
 
 	list_for_each_entry_safe(fp, tmp, &fmb->phys, node) {
 		list_del(&fp->node);

-- 
2.34.1

Re: [PATCH v2 8/8] net: phy: fixed_phy: transition to the faux device interface

[Andrew Lunn]

On Tue, Mar 18, 2025 at 05:01:46PM +0000, Sudeep Holla wrote:
> The net fixed phy driver does not require the creation of a platform
> device. Originally, this approach was chosen for simplicity when the
> driver was first implemented.
> 
> With the introduction of the lightweight faux device interface, we now
> have a more appropriate alternative. Migrate the device to utilize the
> faux bus, given that the platform device it previously created was not
> a real one anyway. This will get rid of the fake platform device.

You were asked to split this up by subsystem. So why is this 8/8?
There are not 7 other patches for netdev.

Please also take a read of:

https://www.kernel.org/doc/html/latest/process/maintainer-netdev.html

    Andrew

---
pw-bot: cr

Re: [PATCH v2 8/8] net: phy: fixed_phy: transition to the faux device interface

[Sudeep Holla]

On Tue, Mar 18, 2025 at 06:12:21PM +0100, Andrew Lunn wrote:
> On Tue, Mar 18, 2025 at 05:01:46PM +0000, Sudeep Holla wrote:
> > The net fixed phy driver does not require the creation of a platform
> > device. Originally, this approach was chosen for simplicity when the
> > driver was first implemented.
> > 
> > With the introduction of the lightweight faux device interface, we now
> > have a more appropriate alternative. Migrate the device to utilize the
> > faux bus, given that the platform device it previously created was not
> > a real one anyway. This will get rid of the fake platform device.
> 
> You were asked to split this up by subsystem. So why is this 8/8?
> There are not 7 other patches for netdev.
>

Sorry for that. I admit this patch unlike other patches in the series is
not dependent on the macro introduced in 1/8. I should have posted this
independent of the series, my bad. I will do that. Thanks!

-- 
Regards,
Sudeep