Re: [PATCH] drm/i915/dsi: Use owned panel/backlight GPIOs in VLV MIPI sequences

[Andy Shevchenko]

On Sun, Oct 18, 2026 at 04:12:40PM -0400, Mike Anderson via B4 Relay wrote:

> On VLV with PPS_BLC_SOC, intel_dsi_vbt_gpio_init() requests the
> backlight and panel enable GPIOs (INT33FC:01 pins 10 and 11) for i915
> itself. Since commit 8241b55f1ded ("drm/i915/dsi: Replace poking of VLV
> GPIOs behind the driver's back") the GPIO elements of the VBT MIPI
> sequences also request their pin through gpiolib, so when a sequence
> toggles one of these two pins the request fails and the toggle is
> dropped:
> 
>   i915 0000:00:02.0: [drm] *ERROR* GPIO index 10 request failed (-EBUSY)
> 
> Before that commit the pad registers were written directly, so the
> sequences could still drive the pins i915 owned.
> 
> The Toshiba Encore 2 WT8-B (Bay Trail, DSI panel) uses pin 10 as the
> panel reset line: MIPI_SEQ_ASSERT_RESET drives it low and
> MIPI_SEQ_DEASSERT_RESET pulses it high-low-high. With every toggle
> failing, the panel is never reset after i915 sends MIPI_SEQ_DISPLAY_OFF
> during takeover and stays black, even though the backlight PWM and both
> enable GPIOs read back as on. The tablet only has a usable display
> with nomodeset.
> 
> When a VLV MIPI sequence targets pin 10 or 11 and i915 holds the
> corresponding descriptor, set it through that descriptor instead of
> requesting the pin a second time.

Ah, nice, this should be solved via using reset-gpio, which is exactly fixed
for the reset shared lines case.

-- 
With Best Regards,
Andy Shevchenko