linux-kernel - Re: [PATCH v4 07/14] drm/imx: dc: Add DPR channel support

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Message-ID: <500852c9-2cd5-4897-a139-4e93988f5469@mailbox.org>
Date: Sun, 2 Nov 2025 17:14:05 +0100
From: Marek Vasut <marek.vasut@...lbox.org>
To: Liu Ying <victor.liu@....com>, Philipp Zabel <p.zabel@...gutronix.de>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
 Sascha Hauer <s.hauer@...gutronix.de>,
 Pengutronix Kernel Team <kernel@...gutronix.de>,
 Fabio Estevam <festevam@...il.com>, Dmitry Baryshkov <lumag@...nel.org>
Cc: dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
 imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, Frank Li <Frank.Li@....com>
Subject: Re: [PATCH v4 07/14] drm/imx: dc: Add DPR channel support

On 10/20/25 4:47 AM, Liu Ying wrote:

Hello Liu,

sorry for my late reply.

>>> +++ b/drivers/gpu/drm/imx/dc/Kconfig
>>> @@ -1,6 +1,7 @@
>>>    config DRM_IMX8_DC
>>>        tristate "Freescale i.MX8 Display Controller Graphics"
>>>        depends on DRM && COMMON_CLK && OF && (ARCH_MXC || COMPILE_TEST)
>>> +    depends on IMX_SCU
>> Can the SCU dependency be made optional,
> 
> I don't think this can be done.  If you grep 'depends on IMX_SCU' in
> kernel, you may find a handful of existing dependancies.

Sure, I do not dispute this part.

But the SCU dependency can be contained in a component of this driver, 
which is not used by MX95, and used only by MX8Q . Then there will be no 
problem.

>> or per-module,
> 
> Well, DRM_IMX8_DC(for the imx8_dc_drm module) depends on IMX_SCU just as
> this patch does.

I assume it shouldn't have to, because the SCU dependency is only 
relevant for the prefetch engine ?

>> or somehow abstracted out (via regmap?),
> 
> Like I replied to your i.MX95 DC patch series's cover letter, SCU accesses
> registers via Cortex-M core instead of Cortex-A core IIUC.  I really don't
> know how to abstract IMX_SCU out, especially via regmap.

The simplest way would be to use regmap_config .reg_read and .reg_write 
, if there is no better way.

>> so iMX95 support can be added into the driver easily too ?
> 
> Like I replied to your i.MX95 DC patch series, I think i.MX95 DC support
> can be in drivers/gpu/drm/imx/dc, but it should be in a separate module
> (something like imx95_dc_drm) plus an additional common module(like
> imx_dc_drm_common).
This design part is something I do not fully understand. Sure, it can be 
two modules, but in the end, the result would have to be capable of 
being compiled into single kernel binary if both modules would be =y in 
Kconfig anyway.