Re: [PATCH] drm/bridge: tc358767: Support input format negotiation hook

[Aradhya Bhatia]

Hi Sam,

Thank you for the suggestion!

On 06-Nov-23 18:08, Sam Ravnborg wrote:
> Hi Aradhya,
> 
> On Tue, Oct 31, 2023 at 12:58:46AM +0530, Aradhya Bhatia wrote:
>> With new connector model, tc358767 will not create the connector, when
>> DRM_BRIDGE_ATTACH_NO_CONNECTOR is set and display-controller driver will
>> rely on format negotiation to setup the encoder format.
>>
>> Add the missing input-format negotiation hook in the
>> drm_bridge_funcs to complete DRM_BRIDGE_ATTACH_NO_CONNECTOR support.
>>
>> Input format is selected to MEDIA_BUS_FMT_RGB888_1X24 as default, as is
>> the case with older model.
>>
>> Reported-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
>> Signed-off-by: Aradhya Bhatia <a-bhatia1@xxxxxx>
>> ---
>>
>> Notes:
>>
>>   * Since I do not have hardware with me, this was just build tested. I would
>>     appreciate it if someone could test and review it, especically somebody, who
>>     uses the bridge for DPI/DSI to eDP format conversion.
>>
>>   * The Toshiba TC358767 bridge is not enabled in arm64 defconfig by default,
>>     when it should be. Hence, I sent a quick patch[0] earlier.
>>
>> [0]: https://lore.kernel.org/all/20231030152834.18450-1-a-bhatia1@xxxxxx/
>>
>>  drivers/gpu/drm/bridge/tc358767.c | 25 +++++++++++++++++++++++++
>>  1 file changed, 25 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/bridge/tc358767.c b/drivers/gpu/drm/bridge/tc358767.c
>> index ef2e373606ba..0affcefdeb1c 100644
>> --- a/drivers/gpu/drm/bridge/tc358767.c
>> +++ b/drivers/gpu/drm/bridge/tc358767.c
>> @@ -1751,6 +1751,30 @@ tc_dpi_atomic_get_input_bus_fmts(struct drm_bridge *bridge,
>>  	return input_fmts;
>>  }
>>  
>> +static u32 *
>> +tc_edp_atomic_get_input_bus_fmts(struct drm_bridge *bridge,
>> +				 struct drm_bridge_state *bridge_state,
>> +				 struct drm_crtc_state *crtc_state,
>> +				 struct drm_connector_state *conn_state,
>> +				 u32 output_fmt,
>> +				 unsigned int *num_input_fmts)
>> +{
>> +	u32 *input_fmts;
>> +
>> +	*num_input_fmts = 0;
>> +
>> +	input_fmts = kcalloc(MAX_INPUT_SEL_FORMATS, sizeof(*input_fmts),
>> +			     GFP_KERNEL);
>> +	if (!input_fmts)
>> +		return NULL;
>> +
>> +	/* This is the DSI/DPI-end bus format */
>> +	input_fmts[0] = MEDIA_BUS_FMT_RGB888_1X24;
>> +	*num_input_fmts = 1;
>> +
>> +	return input_fmts;
>> +}
> 
> You could benefit from using the helper:
> drm_atomic_helper_bridge_propagate_bus_fmt()

You are right!

Upon taking a second look, I realize that the bridge chain works with
MEDIA_BUS_FMT_FIXED bus format, when tc358767 is being used in DPI/DSI
to eDP mode (because the panel-bridge does not have a get_output_bus_fmt
hook, and uses the same helper for its get_input_bus_fmt hook). My patch
creates a deviation from that, by forcing MEDIA_BUS_FMT_RGB888_1X24 even
when eDP is involved.

Using the helper here, will certainly address this deviation.

However, for the DPI/DSI to DP mode, MEDIA_BUS_FMT_RGB888_1X24 bus
format is required, and *just* using the helper as its get_input_bus_fmt
hook, might not be enough.

Since tc358767 is the last bridge in DPI/DSI to DP mode, the
output_fmt parameter get defaulted to MEDIA_BUS_FMT_FIXED too, as there
is no get_output_bus_fmt hook present in the driver. If we simply us
the helper here, the input_fmt will also get set to MEDIA_BUS_FMT_FIXED.
This too is an unwanted deviation.

It seems like the right way to address both the cases, would be by
adding the get_output_bus_fmt hook that sets output_fmt to
MEDIA_BUS_FMT_RGB888_1X24, as well as using the helper as the
get_input_bus_fmt hook.

If this seems good to you too, I will send a new version of Tomi's
series[0] which incorporates this patch.


Regards
Aradhya

[0]:
https://lore.kernel.org/all/20231031-tc358767-v1-0-392081ad9f4b@xxxxxxxxxxxxxxxx/