Re: [PATCH v9 2/2] drm/bridge: add support for lontium lt9211c bridge

[Philipp Zabel <p.zabel@pengutronix.de>]

On Do, 2026-09-24 at 21:29 +0530, vishnu.saini@oss.qualcomm.com wrote:
> From: Yi Zhang <zhanyi@qti.qualcomm.com>
> 
> LT9211C is a Single/Dual-Link DSI/LVDS or Single DPI input to
> Single-Link/Dual-Link DSI/LVDS or Single DPI output bridge chip.
> Extend the existing lontium-lt9211 driver to support DSI-to-LVDS
> bridge configuration by detecting and handling both LT9211 and LT9211C
> variants from a single driver.
> 
> Chip detection in lt9211_read_chipid() is extended to identify the
> LT9211C by its distinct chip ID registers, and cross-checked against
> the chip type requested by the DT compatible string to catch a
> mismatched board/compatible combination.
> 
> Add LT9211C-specific regmap support and use lt9211_chip_data with
> i2c_get_match_data() to provide per-chip configuration.
> 
> Five new functions implement the LT9211C DSI-to-LVDS initialisation
> sequence: lt9211c_configure_rx(), lt9211c_autodetect_rx(),
> lt9211c_configure_timing(), lt9211c_configure_plls() and
> lt9211c_configure_tx().
> 
> Defer the remaining LT9211C initialization to a work item scheduled
> from atomic_enable(), since RX auto-detection requires an active DSI
> stream.

This is still wrong, and I don't understand why you need it.

All scheduling initialization as a work item should allow is for
downstream bridges and/or panels to be atomic_enabled while
lt9211_work_func() is waiting for a vblank interrupt.
They expect the LVDS signal to be active at this point. If LVDS is
enabled at some unknown later point in time by the work item, any
startup timing requirements the panel might have can not be applied
correctly.

Also, deferring initialization as a work item shouldn't have any
influence on the upstream DSI signal. That should already be active
when lt9211c atomic_enable is called. Could it be that there is a bug
in your display controller or DSI bridge driver that causes the DSI
signal to still not be completely active at this point?

> Signed-off-by: Yi Zhang <zhanyi@qti.qualcomm.com>
> Signed-off-by: Nilesh Laad <nilesh.laad@oss.qualcomm.com>
> Signed-off-by: Gopi Botlagunta <venkata.botlagunta@oss.qualcomm.com>
> Signed-off-by: Vishnu Saini <vishnu.saini@oss.qualcomm.com>
> Tested-by: Philipp Zabel <p.zabel@pengutronix.de>

I have not tested this version (yet).


regards
Philipp