Hi Laurent & Daniel :-) On 01/29/2018 11:40 AM, Laurent Pinchart wrote: > 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. > Laurent, do you think we can use "adjusted mode" here in this small patch as the actual 2 "users" of this bridge (rockchip & stm) use both "adjusted mode" in their crtc? >> Many thanks, >> Philippe :-) >> [1] https://patchwork.freedesktop.org/patch/200240/ >> [2] https://patchwork.freedesktop.org/patch/200720/ >> >>> Daniel, what's your opinion on this ? >>> Daniel, any opinion on the adjusted_mode usage? Many thanks to both of you, Philippe :-) >>>> --- >>>> 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); > _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
