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

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Message-ID: <b642d226-1312-4846-a353-622a7e21939e@ti.com>
Date:   Wed, 8 Nov 2023 00:01:44 +0530
From:   Aradhya Bhatia <a-bhatia1@...com>
To:     Sam Ravnborg <sam@...nborg.org>
CC:     Nishanth Menon <nm@...com>, Vignesh Raghavendra <vigneshr@...com>,
        Devarsh Thakkar <devarsht@...com>,
        Jan Kiszka <jan.kiszka@...mens.com>,
        DRI Development List <dri-devel@...ts.freedesktop.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Robert Foss <rfoss@...nel.org>,
        Francesco Dolcini <francesco@...cini.it>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Jonas Karlman <jonas@...boo.se>,
        Maxime Ripard <mripard@...nel.org>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Jayesh Choudhary <j-choudhary@...com>,
        Tomi Valkeinen <tomba@...nel.org>,
        Linux Kernel List <linux-kernel@...r.kernel.org>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        Jyri Sarha <jyri.sarha@....fi>
Subject: Re: [PATCH] drm/bridge: tc358767: Support input format negotiation
 hook

Hi Sam,

On 07-Nov-23 21:11, Sam Ravnborg wrote:
> Hi Aradhya,
> 
> On Tue, Nov 07, 2023 at 01:17:03AM +0530, Aradhya Bhatia wrote:
>> 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@...mens.com>
>>>> Signed-off-by: Aradhya Bhatia <a-bhatia1@...com>
>>>> ---
>>>>
>>>> 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@ti.com/
>>>>
>>>>  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.
> 
> I never managed to fully wrap my head around the bus fmt negotiation,
> and as I am trying to recover from a flu this is not the time to try.
> Your explanations sounds like you have grasped it so I suggest to move
> ahead.
> 

Sure, I will send a new version.

Hope you recover soon! =)

Regards
Aradhya