linux-kernel - Re: [PATCH v2 2/2] drm/bridge: add support for lontium lt9211c bridge

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Message-ID: <d2c9cac9-17cc-4bc6-8322-bc43edbf45d1@mailbox.org>
Date: Fri, 7 Nov 2025 16:11:15 +0100
From: Marek Vasut <marek.vasut@...lbox.org>
To: Nilesh Laad <nilesh.laad@....qualcomm.com>
Cc: Andrzej Hajda <andrzej.hajda@...el.com>,
 Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>,
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Marek Vasut <marex@...x.de>,
 dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, venkata.valluru@....qualcomm.com,
 jessica.zhang@....qualcomm.com, Yi Zhang <zhanyi@....qualcomm.com>,
 Gopi Botlagunta <venkata.botlagunta@....qualcomm.com>
Subject: Re: [PATCH v2 2/2] drm/bridge: add support for lontium lt9211c bridge

On 11/7/25 2:52 PM, Nilesh Laad wrote:
> On Fri, Nov 07, 2025 at 02:20:58PM +0100, Marek Vasut wrote:
>> On 11/7/25 2:02 PM, Nilesh Laad wrote:
>>> From: Yi Zhang <zhanyi@....qualcomm.com>
>>>
>>> LT9211c is a Single/Dual-Link DSI/LVDS or Single DPI input to
>>> Single-link/Dual-Link DSI/LVDS or Single DPI output bridge chip.
>>> Add support for DSI to LVDS bridge configuration.
>> How does this differ from existing drivers/gpu/drm/bridge/lontium-lt9211.c ?
>> Can existing lt9211 driver be extended instead ? If not, why ? Details
>> please ...
> LT9211 and LT9211C differ completely in register programming sequences.
> Even lontium mentioned that register configuration are different for lt9211 and lt9211c.

Lontium seems to often suggest, that users should use their provided 
register patches without thinking about the content at all.

Do you have access to the register documentation, and can you compare 
LT9211 and LT9211C register layout? Are they identical or do they differ?

> Nearly every function would require duplicated logic with if (chip_type) branching,
> as register sequence are completely different.
> Having both sequences in single file is not looking good, hence want to merge as separate driver.

Can we somehow use regmap_register_patch() and register patches in 
driver data to avoid duplication ?

-- 
Best regards,
Marek Vasut