linux-kernel - Re: [PATCH v3] drm/bridge: ti-sn65dsi86: Add HPD for DisplayPort connector type

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Message-ID: <3dd0f1dc-441c-47e7-bfe5-bd2791c87895@kernel.org>
Date: Sun, 1 Jun 2025 13:09:22 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Geert Uytterhoeven <geert@...ux-m68k.org>,
 Jayesh Choudhary <j-choudhary@...com>
Cc: dianders@...omium.org, andrzej.hajda@...el.com,
 neil.armstrong@...aro.org, rfoss@...nel.org,
 Laurent.pinchart@...asonboard.com, dri-devel@...ts.freedesktop.org,
 tomi.valkeinen@...asonboard.com, max.krummenacher@...adex.com,
 ernestvanhoecke@...il.com, jonas@...boo.se, jernej.skrabec@...il.com,
 maarten.lankhorst@...ux.intel.com, mripard@...nel.org, tzimmermann@...e.de,
 airlied@...il.com, simona@...ll.ch, kieran.bingham+renesas@...asonboard.com,
 linux-kernel@...r.kernel.org, max.oss.09@...il.com, devarsht@...com,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>,
 "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
 <devicetree@...r.kernel.org>
Subject: Re: [PATCH v3] drm/bridge: ti-sn65dsi86: Add HPD for DisplayPort
 connector type

On 30/05/2025 09:55, Geert Uytterhoeven wrote:
> Hi Jayesh,
> 
> CC devicetree
> 
> On Fri, 30 May 2025 at 04:54, Jayesh Choudhary <j-choudhary@...com> wrote:
>> On 29/05/25 16:34, Jayesh Choudhary wrote:
>>> By default, HPD was disabled on SN65DSI86 bridge. When the driver was
>>> added (commit "a095f15c00e27"), the HPD_DISABLE bit was set in pre-enable
>>> call which was moved to other function calls subsequently.
>>> Later on, commit "c312b0df3b13" added detect utility for DP mode. But with
>>> HPD_DISABLE bit set, all the HPD events are disabled[0] and the debounced
>>> state always return 1 (always connected state).
>>>
>>> Set HPD_DISABLE bit conditionally based on "no-hpd" property.
>>> Since the HPD_STATE is reflected correctly only after waiting for debounce
>>> time (~100-400ms) and adding this delay in detect() is not feasible
>>> owing to the performace impact (glitches and frame drop), remove runtime
>>> calls in detect() and add hpd_enable()/disable() bridge hooks with runtime
>>> calls, to detect hpd properly without any delay.
>>>
>>> [0]: <https://www.ti.com/lit/gpn/SN65DSI86> (Pg. 32)
>>>
>>> Fixes: c312b0df3b13 ("drm/bridge: ti-sn65dsi86: Implement bridge connector operations for DP")
>>> Cc: Max Krummenacher <max.krummenacher@...adex.com>
>>> Signed-off-by: Jayesh Choudhary <j-choudhary@...com>
>>> ---
>>>
>>> Changelog v2->v3:
>>> - Change conditional based on no-hpd property to address [1]
>>> - Remove runtime calls in detect() with appropriate comments
>>> - Add hpd_enable() and hpd_disable() in drm_bridge_funcs
>>> - Not picking up "Tested-by" tag as there are new changes
>>>
>>> v2 patch link:
>>> <https://lore.kernel.org/all/20250508115433.449102-1-j-choudhary@ti.com/>
>>>
>>> [1]: <https://lore.kernel.org/all/mwh35anw57d6nvre3sguetzq3miu4kd43rokegvul7fk266lys@5h2euthpk7vq/>
> 
> Thanks for your patch!
> 
>>> This would also require dts changes in all the nodes of sn65dsi86
>>> to ensure that they have no-hpd property.
>>
>> DTS patch is posted now:
>> <https://lore.kernel.org/all/20250529112423.484232-1-j-choudhary@ti.com/>


This does not work like that. You cannot change DTS in other projects,
other users of this ABI. What's more, you cannot change old DTS, unless
you have a time machine.


Best regards,
Krzysztof