Re: [Intel-gfx] [v4] drm/i915/dsi: Send proper brightness value via MIPI DCS command

["Lee, Shawn C" <shawn.c.lee@intel.com>]

On Wed, 18 Aug 2021, Jani Nikula <jani.nikula@linux.intel.com> wrote:
>On Fri, 13 Aug 2021, Lee Shawn C <shawn.c.lee@intel.com> wrote:
>> Driver has to swap the endian before send brightness level value to 
>> tcon.
>>
>> v2: Use __be16 instead of u16 to fix sparse warning.
>>
>> Reported-by: kernel test robot <lkp@intel.com>
>> Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
>> Cc: Jani Nikula <jani.nikula@linux.intel.com>
>> Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
>> Cc: Cooper Chiou <cooper.chiou@intel.com>
>> Cc: William Tseng <william.tseng@intel.com>
>> Signed-off-by: Lee Shawn C <shawn.c.lee@intel.com>
>> ---
>>  drivers/gpu/drm/i915/display/intel_dsi_dcs_backlight.c | 3 +--
>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> 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 cd85520d36e2..71c2adfa8931 100644
>> --- a/drivers/gpu/drm/i915/display/intel_dsi_dcs_backlight.c
>> +++ b/drivers/gpu/drm/i915/display/intel_dsi_dcs_backlight.c
>> @@ -66,10 +66,9 @@ static void dcs_set_backlight(const struct 
>> drm_connector_state *conn_state, u32  {
>>  	struct intel_dsi *intel_dsi = enc_to_intel_dsi(to_intel_encoder(conn_state->best_encoder));
>>  	struct mipi_dsi_device *dsi_device;
>> -	u8 data = level;
>> +	__be16 data = cpu_to_be16(level);
>
>Just discussed this with Vandita. Both the set and get brightness need to be adjusted, and the read/write size (one or two bytes) has to depend on the precision. From MIPI DCS spec:
>
>	Note: It is up to display manufacturer to determine the
>	implementation of this register and background logic. Only one
>	parameter shall be sent for devices that support 8-bit
>	brightness levels. Two parameters shall be sent for devices that
>	support between 9-bit and 16-bit brightness levels.
>
>BR,
>Jani.
>

OK! We will send a patch that modify read/write size depend on precision setting.

Best regards,
Shawn

>
>>  	enum port port;
>>  
>> -	/* FIXME: Need to take care of 16 bit brightness level */
>>  	for_each_dsi_port(port, intel_dsi->dcs_backlight_ports) {
>>  		dsi_device = intel_dsi->dsi_hosts[port]->device;
>>  		mipi_dsi_dcs_write(dsi_device, MIPI_DCS_SET_DISPLAY_BRIGHTNESS,
>
>--
>Jani Nikula, Intel Open Source Graphics Center