[RFC][PATCH 0/7] drm/bridge: Add support for selecting DSI host HS clock from DSI bridge

[Marek Vasut <marex@denx.de>]

This patch series attempts to address a problem of missing support for DSI
bridge-to-bridge or panel-to-bridge clock frequency negotiation. The problem
has two variants.

First, a DSI->to->x bridge derives its own internal clock from DSI HS clock,
but the DSI HS clock cannot be set to arbitrary values. TS358767 is one such
bridge in case it operates without Xtal. In that case, the TC358767 driver
must be able to negotiate the specific suitable DSI HS clock frequency for
the chip.

Second, both DSI->to->x bridges and DSI hosts currently calculate, or rather
guess and hope they both guess the same number as their neighbor, the DSI HS
clock frequency from form of PLL=(width * height * bpp / lanes / 2). This is
dangerous, since the PLL capabilities on both ends of the DSI bus might differ
and the DSI host could easily end up generating wildly different clock than
what the DSI bridge/panel expects to receive.

This series attempts to address these negotiation problems by extending the
existing .atomic_get_input_bus_fmts callback into .atomic_get_input_bus_cfgs
callback in struct drm_bridge_funcs {}. The extended version returns not only
a list of a list of bus formats supported by a bridge, but the entire list of
struct drm_bus_cfg, which currently contains format and bus flags, but can be
extended with other members, like desired clock frequency, as required.

This series demonstrates such extension by adding the support for negotiating
the DSI clock and by implementing such support in DW DSI Host and TC358767 DSI
bridge.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
Cc: Maxime Ripard <maxime@cerno.tech>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Cc: Sam Ravnborg <sam@ravnborg.org>

TC358767 part depends on:
https://patchwork.freedesktop.org/series/100372

Marek Vasut (7):
  drm/bridge: Pass struct drm_bus_cfg to select_bus_fmt_recursive()
  drm/bridge: Add new atomic_get_input_bus_cfgs callback
  drm/bridge: Extend struct drm_bus_cfg with clock field
  drm/bridge: dw-mipi-dsi: Move PLL setup into atomic_enable
  drm/bridge: dw-mipi-dsi: Pass bridge state into
    dw_mipi_dsi_get_lane_mbps()
  drm/bridge: dw-mipi-dsi: Prefer DSI bus clock settings from
    bridge_state
  drm/bridge: tc358767: Add support for PLL clock derivation from DSI HS
    clock

 drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c | 22 +++--
 drivers/gpu/drm/bridge/tc358767.c             | 97 +++++++++++++++----
 drivers/gpu/drm/drm_bridge.c                  | 78 +++++++++++----
 .../gpu/drm/rockchip/dw-mipi-dsi-rockchip.c   |  1 +
 drivers/gpu/drm/stm/dw_mipi_dsi-stm.c         | 17 ++--
 include/drm/bridge/dw_mipi_dsi.h              |  2 +
 include/drm/drm_atomic.h                      |  5 +
 include/drm/drm_bridge.h                      | 42 ++++++++
 8 files changed, 214 insertions(+), 50 deletions(-)

-- 
2.34.1