[PATCH v3 0/2] platform/x86: dell-uart-backlight: fall back to PCH PWM on UART timeout

[chitranshmandhaniya]

From: Chitransh Mandhaniya <Chitransh_Mandhaniya@xxxxxxxx>

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.

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

v1 -> v2:
  - Use __free(pci_dev_put) for automatic PCI device cleanup (Ilpo)
  - Replace 0x10 with SZ_16, 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
    so the probe function reads more clearly (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   | 156 +++++++++++++++---
 1 file changed, 133 insertions(+), 23 deletions(-)

-- 
2.43.0