| Message ID | 20241115160641.74074-2-dse@thaumatec.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | drm/bridge: tc358775: Remove burst mode support | expand |
On 15/11/2024 17:06, Daniel Semkowicz wrote: > Current tc358775 bridge driver implementation assumes that DSI clock > is used as a source for LVDS pixel clock. Moreover, clock divider > PCLKDIV has a hard-coded value. This means that driver expects DSI > clock to always match a panel pixel clock. With such assumption, LVDS > pixel clock is configured to be (DSI pixel clock / 3) for single link. > This is true for DSI non-burst video modes. In burst mode, DSI host > is allowed to set transmission rate higher than pixel clock to allow > shorter data bursts. When the transmission rate is higher than expected > by the bridge, LVDS output timings are still configured for the lower > frequency, but the output is clocked with the higher one. In most cases, > bad LVDS timings cause incorrect panel operation. > > Remove support for burst mode, so the non-burst mode is used by DSI > host by default. Burst mode is supported by the bridge itself, > but requires proper implementation in the driver to operate correctly > in all scenarios. > > Fixes: a4ed72e85c46 ("drm/bridge: tc358775: Add burst and low-power modes") > Signed-off-by: Daniel Semkowicz <dse@thaumatec.com> > --- > > drivers/gpu/drm/bridge/tc358775.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/drivers/gpu/drm/bridge/tc358775.c b/drivers/gpu/drm/bridge/tc358775.c > index 0b4efaca6d682..7496681c7b883 100644 > --- a/drivers/gpu/drm/bridge/tc358775.c > +++ b/drivers/gpu/drm/bridge/tc358775.c > @@ -632,8 +632,7 @@ static int tc_attach_host(struct tc_data *tc) > > dsi->lanes = tc->num_dsi_lanes; > dsi->format = MIPI_DSI_FMT_RGB888; > - dsi->mode_flags = MIPI_DSI_MODE_VIDEO | MIPI_DSI_MODE_VIDEO_BURST | > - MIPI_DSI_MODE_LPM; > + dsi->mode_flags = MIPI_DSI_MODE_VIDEO | MIPI_DSI_MODE_LPM; > > /* > * The hs_rate and lp_rate are data rate values. The HS mode is Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
diff --git a/drivers/gpu/drm/bridge/tc358775.c b/drivers/gpu/drm/bridge/tc358775.c index 0b4efaca6d682..7496681c7b883 100644 --- a/drivers/gpu/drm/bridge/tc358775.c +++ b/drivers/gpu/drm/bridge/tc358775.c @@ -632,8 +632,7 @@ static int tc_attach_host(struct tc_data *tc) dsi->lanes = tc->num_dsi_lanes; dsi->format = MIPI_DSI_FMT_RGB888; - dsi->mode_flags = MIPI_DSI_MODE_VIDEO | MIPI_DSI_MODE_VIDEO_BURST | - MIPI_DSI_MODE_LPM; + dsi->mode_flags = MIPI_DSI_MODE_VIDEO | MIPI_DSI_MODE_LPM; /* * The hs_rate and lp_rate are data rate values. The HS mode is
Current tc358775 bridge driver implementation assumes that DSI clock is used as a source for LVDS pixel clock. Moreover, clock divider PCLKDIV has a hard-coded value. This means that driver expects DSI clock to always match a panel pixel clock. With such assumption, LVDS pixel clock is configured to be (DSI pixel clock / 3) for single link. This is true for DSI non-burst video modes. In burst mode, DSI host is allowed to set transmission rate higher than pixel clock to allow shorter data bursts. When the transmission rate is higher than expected by the bridge, LVDS output timings are still configured for the lower frequency, but the output is clocked with the higher one. In most cases, bad LVDS timings cause incorrect panel operation. Remove support for burst mode, so the non-burst mode is used by DSI host by default. Burst mode is supported by the bridge itself, but requires proper implementation in the driver to operate correctly in all scenarios. Fixes: a4ed72e85c46 ("drm/bridge: tc358775: Add burst and low-power modes") Signed-off-by: Daniel Semkowicz <dse@thaumatec.com> --- drivers/gpu/drm/bridge/tc358775.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)