On Mon, 4 Apr 2022 at 21:21, Sankeerth Billakanti (QUIC) <quic_sbillaka@xxxxxxxxxxx> wrote: > > Hi Doug, > > > On Wed, Mar 30, 2022 at 11:02 PM Sankeerth Billakanti (QUIC) > > <quic_sbillaka@xxxxxxxxxxx> wrote: > > > > > > Hi Dmitry, > > > > > > > On Wed, 30 Mar 2022 at 19:04, Sankeerth Billakanti > > > > <quic_sbillaka@xxxxxxxxxxx> wrote: > > > > > > > > > > The panel-edp driver modes needs to be validated differently from > > > > > DP because the link capabilities are not available for EDP by that time. > > > > > > > > > > Signed-off-by: Sankeerth Billakanti <quic_sbillaka@xxxxxxxxxxx> > > > > > > > > This should not be necessary after > > > > > > https://patchwork.freedesktop.org/patch/479261/?series=101682&rev=1. > > > > Could you please check? > > > > > > > > > > The check for DP_MAX_PIXEL_CLK_KHZ is not necessary anymore but we > > > need to return early for eDP because unlike DP, eDP context will not > > > have the information about the number of lanes and link clock. > > > > > > So, I will modify the patch to return after the DP_MAX_PIXEL_CLK_KHZ > > check if is_eDP is set. > > > > I haven't walked through all the relevant code but something you said above > > sounds strange. You say that for eDP we don't have info about the number > > of lanes? We _should_. > > > > It's certainly possible to have a panel that supports _either_ 1 or 2 lanes but > > then only physically connect 1 lane to it. ...or you could have a panel that > > supports 2 or 4 lanes and you only connect 1 lane. > > See, for instance, ti_sn_bridge_parse_lanes. There we assume 4 lanes but if > > a "data-lanes" property is present then we can use that to know that fewer > > lanes are physically connected. > > > > It's also possible to connect more lanes to a panel than it supports. > > You could connect 2 lanes to it but then it only supports 1. This case needs to > > be handled as well... > > > > I was referring to the checks we do for DP in dp_bridge_mode_valid. We check if the > Link bandwidth can support the pixel bandwidth. For an external DP connection, the > Initial DPCD/EDID read after cable connection will return the sink capabilities like link > rate, lane count and bpp information that are used to we filter out the unsupported > modes from the list of modes from EDID. > > For eDP case, the dp driver performs the first dpcd read during bridge_enable. The > dp_bridge_mode_valid function is executed before bridge_enable and hence does > not have the full link or the sink capabilities information like external DP connection, > by then. It sounds to me like we should emulate the HPD event for eDP to be handled earlier than the get_modes()/prepare() calls are attempted. However this might open another can of worms. > So, we need to proceed with the reported mode for eDP. Well... Even if during the first call to get_modes() the DPCD is not read, during subsequent calls the driver has necessary information, so it can proceed with all the checks, can't it? -- With best wishes Dmitry
