linux-kernel - Re: [PATCH v4 2/4] drm/panel: Add refcount support

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Message-ID: <20250527-winged-prawn-of-virtuosity-d11a47@houat>
Date: Tue, 27 May 2025 16:57:51 +0200
From: Maxime Ripard <mripard@...nel.org>
To: Jani Nikula <jani.nikula@...ux.intel.com>
Cc: Anusha Srivatsa <asrivats@...hat.com>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Jessica Zhang <quic_jesszhan@...cinc.com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Thomas Zimmermann <tzimmermann@...e.de>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, dri-devel@...ts.freedesktop.org, 
	linux-kernel@...r.kernel.org, Luca Ceresoli <luca.ceresoli@...tlin.com>
Subject: Re: [PATCH v4 2/4] drm/panel: Add refcount support

On Tue, May 20, 2025 at 01:09:47PM +0300, Jani Nikula wrote:
> 
> Maxime -
> 
> I'm cutting a lot of context here. Not because I don't think it deserves
> an answer, but because I seem to be failing at communication.
> 
> On Mon, 19 May 2025, Maxime Ripard <mripard@...nel.org> wrote:
> > You still haven't explained why it would take anything more than
> > registering a dumb device at probe time though.
> 
> With that, do you mean a dumb struct device, or any struct device with a
> suitable lifetime, that we'd pass to devm_drm_panel_alloc()?
> 
> Is using devm_drm_panel_alloc() like that instead of our own allocation
> with drm_panel_init() the main point of contention for you? If yes, we
> can do that.

Yeah, I was thinking of something along the lines of:

const struct drm_panel_funcs dummy_funcs = {};

struct drm_panel *register_panel() {
    struct faux_device *faux;
    struct drm_panel *panel;
    int ret;

    faux = faux_device_create(...);
    if IS_ERR(faux)
       return ERR_CAST(faux);

    return __devm_drm_panel_alloc(&faux->dev, sizeof(*panel), 0, &dummy_funcs, $CONNECTOR_TYPE);
}

And you have a panel, under your control, with exactly the same
setup than anyone else.

Maxime

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