Hi Linus, Thank you for the patch. On Friday, 20 October 2017 09:59:41 EEST Linus Walleij wrote: > This extends the dumb VGA DAC bridge to handle the THS8134A > and THS8134B VGA DACs in addition to those already handled. > > The THS8134A, THS8134B and as it turns out also THS8135 need to > have data clocked out at the negative edge of the clock pulse, > since they clock it into the DAC at the positive edge (so by > then it needs to be stable) so we need some extra logic to flag > this on the connector to the driver. > > The semantics of the flag DRM_BUS_FLAG_PIXDATA_NEGEDGE in > <drm/drm_connector.h> clearly indicates that this flag tells > when to *drive* the data, not when the receiver *reads* it, > so the TI variants needs to be handled like this. > > Introduce a variant struct and contain the information there, > and add a bit of helpful comments about how this works so > people will get it right when adding new DACs or connectiong > new display drivers to DACs. > > The fact that THS8135 might be working on some systems today > is probably due to the fact that the display driver cannot > configure when the data is clocked out and the electronics > have simply been designed around it so it works anyways. > > The phenomenon is very real on the ARM reference designs using > PL111 where the hardware can control which edge to push out > the data. > > Cc: Laurent Pinchart <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx> > Cc: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx> > Cc: Maxime Ripard <maxime.ripard@xxxxxxxxxxxxxxxxxx> > Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx> > --- > ChangeLog v2->v3: > - Move const specifier. > - Cut one line of code assigning bus flags. > - Preserve the "ti,ths8135" compatible for elder device trees. > ChangeLog v1->v2: > - Alphabetize includes > - Use a u32 with the bus polarity flags and just encode the > polarity using the DRM define directly. > - Rename vendor_data to vendor_info. > - Simplify assignment of the flag as it is just a simple > u32 now. > - Probe all TI variants on the "ti,ths813x" wildcard for now, > we only need to know that the device is in this family to > set the clock edge flag right. > --- > drivers/gpu/drm/bridge/dumb-vga-dac.c | 55 +++++++++++++++++++++++++++++--- > 1 file changed, 51 insertions(+), 4 deletions(-) > > diff --git a/drivers/gpu/drm/bridge/dumb-vga-dac.c > b/drivers/gpu/drm/bridge/dumb-vga-dac.c index 831a606c4706..2622e2f778d1 > 100644 > --- a/drivers/gpu/drm/bridge/dumb-vga-dac.c > +++ b/drivers/gpu/drm/bridge/dumb-vga-dac.c [snip] > @@ -55,7 +65,8 @@ static int dumb_vga_get_modes(struct drm_connector > *connector) } > > drm_mode_connector_update_edid_property(connector, edid); > - return drm_add_edid_modes(connector, edid); > + connector->display_info.bus_flags |= vga->variant->clk_edge_latch; > + retturn drm_add_edid_modes(connector, edid); Have you compiled this ? > fallback: > /* [snip] -- Regards, Laurent Pinchart _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
