Hi Philippe, On Monday, 29 January 2018 12:17:37 EET Philippe CORNU wrote: > On 01/29/2018 10:46 AM, Laurent Pinchart wrote: > > On Thursday, 25 January 2018 17:55:04 EET Philippe Cornu wrote: > > > >> The "adjusted_mode" clock value (ie the real pixel clock) is more > >> accurate than "mode" clock value (ie the panel/bridge requested > >> clock value). It offers a better preciseness for timing > >> computations and allows to reduce the extra dsi bandwidth in > >> burst mode (from ~20% to ~10-12%, hw platform dependant). > >> > >> Signed-off-by: Philippe Cornu <philippe.cornu@xxxxxx> > > > > The adjusted mode is documented as > > > > /** > > * @adjusted_mode: > > * > > * Internal display timings which can be used by the driver to handle > > * differences between the mode requested by userspace in @mode and what > > * is actually programmed into the hardware. It is purely driver > > * implementation defined what exactly this adjusted mode means. Usually > > * it is used to store the hardware display timings used between the > > * CRTC and encoder blocks. > > */ > > > > This is easy to handle when the CRTC and encoder are controlled by the > > same driver, as the field is "implementation defined" by a single driver > > . However, when using bridges, there are two drivers involved, and they > > must both agree to meaningfully use the adjusted mode. I can't see how to > > do so without standardizing the meaning of the adjusted mode field. > > This is exactly the reason why my first implementation used the dsi > bridge "optional pixel clock" instead of the adjusted_mode (see [1]) > > But after digging more into the drm source code, I think using > adjusted_mode instead of the pixel clock here brings more advantages > because: > * adjusted_mode is an argument of bridge mode_set() probably for being > used in any manner, maybe like this :) > * if the bridge "user" (crtc or a master bridge drivers) does not need > to modify its adjusted_mode then mode & adjusted_mode mode_set() > arguments will have the same values so "no consequence" for the bridge. > * if the bridge "user" (crtc or master bridge drivers) needs to adjust > any value of the mode then this adjustment is available for the bridge. Remember that there can be multiple chained bridges, and a single adjusted mode field. > * rockchip crtc updates a part of the mode (the clock), stm is doing the > same (see [2]) but any future "user" of the dw_mipi_dsi bridge can > adjust something else (blankings...) and the dw_mipi_dsi bridge will be > then aware of... > > But maybe it is a wrong usage of the "adjusted_mode offer"... I don't disagree that there's a need for using adjusted values, but I believe we need to create a clear API to do so. Using the adjust_mode field as-is when it's clearly documented as being implementation-defined is asking for trouble. > Many thanks, > Philippe :-) > [1] https://patchwork.freedesktop.org/patch/200240/ > [2] https://patchwork.freedesktop.org/patch/200720/ > > > Daniel, what's your opinion on this ? > > > >> --- > >> Note: This patch replaces "drm/bridge/synopsys: dsi: add optional pixel > >> clock" > >> > >> drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c | 12 ++++++------ > >> 1 file changed, 6 insertions(+), 6 deletions(-) > >> > >> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c > >> b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c index > >> ed8af32f8e52..b926b62e9e33 100644 > >> --- a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c > >> +++ b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c > >> @@ -707,20 +707,20 @@ static void dw_mipi_dsi_bridge_mode_set(struct > >> drm_bridge *bridge, > >> > >> clk_prepare_enable(dsi->pclk); > >> > >> - ret = phy_ops->get_lane_mbps(priv_data, mode, dsi->mode_flags, > >> + ret = phy_ops->get_lane_mbps(priv_data, adjusted_mode, > >> dsi->mode_flags, > >> dsi->lanes, dsi->format, &dsi->lane_mbps); > >> if (ret) > >> DRM_DEBUG_DRIVER("Phy get_lane_mbps() failed\n"); > >> > >> pm_runtime_get_sync(dsi->dev); > >> dw_mipi_dsi_init(dsi); > >> > >> - dw_mipi_dsi_dpi_config(dsi, mode); > >> + dw_mipi_dsi_dpi_config(dsi, adjusted_mode); > >> dw_mipi_dsi_packet_handler_config(dsi); > >> dw_mipi_dsi_video_mode_config(dsi); > >> - dw_mipi_dsi_video_packet_config(dsi, mode); > >> + dw_mipi_dsi_video_packet_config(dsi, adjusted_mode); > >> dw_mipi_dsi_command_mode_config(dsi); > >> - dw_mipi_dsi_line_timer_config(dsi, mode); > >> - dw_mipi_dsi_vertical_timing_config(dsi, mode); > >> + dw_mipi_dsi_line_timer_config(dsi, adjusted_mode); > >> + dw_mipi_dsi_vertical_timing_config(dsi, adjusted_mode); > >> dw_mipi_dsi_dphy_init(dsi); > >> dw_mipi_dsi_dphy_timing_config(dsi); > >> > >> @@ -734,7 +734,7 @@ static void dw_mipi_dsi_bridge_mode_set(struct > >> drm_bridge *bridge, > >> > >> dw_mipi_dsi_dphy_enable(dsi); > >> > >> - dw_mipi_dsi_wait_for_two_frames(mode); > >> + dw_mipi_dsi_wait_for_two_frames(adjusted_mode); > >> > >> /* Switch to cmd mode for panel-bridge pre_enable & panel prepare */ > >> dw_mipi_dsi_set_mode(dsi, 0); -- Regards, Laurent Pinchart _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
