Re: [Intel-gfx] [PATCH v3] drm/i915/dsi: transmit brightness command in HS state

[Jani Nikula <jani.nikula@linux.intel.com>]

On Wed, 10 Nov 2021, William Tseng <william.tseng@intel.com> wrote:
> In Video Mode, if DSI transcoder is set to transmit packets
> in LP Escape mode, screen flickering would be obseved when
> brightness commands are continuously and quickly transmitted
> to a panel.
>
> The problem may be resolved by changing the mode to transmit
> packets from Low Power to HS.
>
> Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
> Cc: Lee Shawn C <shawn.c.lee@intel.com>
> Cc: Cooper Chiou <cooper.chiou@intel.com>
> Signed-off-by: William Tseng <william.tseng@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dsi_dcs_backlight.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dsi_dcs_backlight.c b/drivers/gpu/drm/i915/display/intel_dsi_dcs_backlight.c
> index f61ed82e8867..7d234429e71e 100644
> --- a/drivers/gpu/drm/i915/display/intel_dsi_dcs_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_dsi_dcs_backlight.c
> @@ -71,6 +71,7 @@ static void dcs_set_backlight(const struct drm_connector_state *conn_state, u32
>  	u8 data[2] = {};
>  	enum port port;
>  	size_t len = panel->backlight.max > U8_MAX ? 2 : 1;
> +	unsigned long mode_flags;
>  
>  	if (len == 1) {
>  		data[0] = level;
> @@ -81,8 +82,11 @@ static void dcs_set_backlight(const struct drm_connector_state *conn_state, u32
>  
>  	for_each_dsi_port(port, intel_dsi->dcs_backlight_ports) {
>  		dsi_device = intel_dsi->dsi_hosts[port]->device;
> +		mode_flags = dsi_device->mode_flags;
> +		dsi_device->mode_flags &= ~MIPI_DSI_MODE_LPM;
>  		mipi_dsi_dcs_write(dsi_device, MIPI_DCS_SET_DISPLAY_BRIGHTNESS,
>  				   &data, len);
> +		dsi_device->mode_flags = mode_flags;

I realize we don't really have a clear picture how to manage
->mode_flags or MIPI_DSI_MODE_LPM in particular, but this seems like the
safest option for now.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>

I'll push once CI results are in; had to request a re-run.



>  	}
>  }

-- 
Jani Nikula, Intel Open Source Graphics Center