[PATCH v4 0/2] platform/x86: dell-uart-backlight: fall back to PCH PWM on UART timeout

[chitranshmandhaniya@gmail.com]

From: Chitransh Mandhaniya <Chitransh_Mandhaniya@dell.com>

Some Dell OptiPlex AIO 7410 (35W) ship with DELL0501 in ACPI but no
physical UART scalar board, leaving the machine with zero backlight
control after the UART probe times out.

Patch 1 is a preparatory refactor that extracts the UART initialization
sequence into dell_uart_bl_init() so the probe function can inspect its
return value.

Patch 2 adds a PCH PWM fallback path: when dell_uart_bl_init() returns
-ETIMEDOUT, the driver reads the Intel PCH BLC_PWM registers and
registers a BACKLIGHT_PLATFORM device.

v3 -> v4:
  - Revert __free(pci_dev_put) to manual pci_dev_put() calls to fix
    build error when CONFIG_PCI is disabled (kernel test robot)

v2 -> v3:
  - Split into two patches: preparatory refactor + fallback (Ilpo)

v1 -> v2:
  - Use SZ_16 instead of 0x10, add linux/sizes.h (Ilpo)
  - Name BIT(31) as PCH_BLC_PWM_ENABLE (Ilpo)
  - Fix double-space in block comment (Ilpo)
  - Reduce devm_backlight_device_register() to fewer lines (Ilpo)
  - Extract dell_uart_bl_init() for the normal UART backlight path (Ilpo)

Chitransh Mandhaniya (2):
  platform/x86: dell-uart-backlight: extract dell_uart_bl_init() from
    probe
  platform/x86: dell-uart-backlight: fall back to PCH PWM on UART
    timeout

 .../platform/x86/dell/dell-uart-backlight.c   | 158 +++++++++++++++---
 1 file changed, 135 insertions(+), 23 deletions(-)

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2.43.0