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@ideasonboard.com Cc: Bartosz Golaszewski bgolaszewski@baylibre.com Cc: Maxime Ripard maxime.ripard@free-electrons.com Signed-off-by: Linus Walleij linus.walleij@linaro.org
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]