linux-kernel - Re: [PATCH 2/2] drm: xlnx: zynqmp_kms: set preferred

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Message-ID: <52b59334-9c93-4273-b142-41c14a7a2c3c@suse.de>
Date: Tue, 6 Jan 2026 08:38:00 +0100
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Mikko Rapeli <mikko.rapeli@...aro.org>, dri-devel@...ts.freedesktop.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Michal Simek <michal.simek@....com>,
 Bill Mills <bill.mills@...aro.org>,
 Ilias Apalodimas <ilias.apalodimas@...aro.org>,
 Anatoliy Klymenko <anatoliy.klymenko@....com>, stable@...r.kernel.org
Subject: Re: [PATCH 2/2] drm: xlnx: zynqmp_kms: set preferred_depth to 16 bpp

Hi

Am 05.12.25 um 13:37 schrieb Mikko Rapeli:
> Xorg fails to start with defaults on AMD KV260, /var/log/Xorg.0.log:
>
> [    23.491] (II) Loading /usr/lib/xorg/modules/drivers/fbdev_drv.so
> [    23.491] (II) Module fbdev: vendor="X.Org Foundation"
> [    23.491]    compiled for 1.21.1.18, module version = 0.5.1
> [    23.491]    Module class: X.Org Video Driver
> [    23.491]    ABI class: X.Org Video Driver, version 25.2
> [    23.491] (II) modesetting: Driver for Modesetting Kernel Drivers:
> kms
> [    23.491] (II) FBDEV: driver for framebuffer: fbdev
> [    23.510] (II) modeset(0): using drv /dev/dri/card1
> [    23.511] (WW) Falling back to old probe method for fbdev
> [    23.511] (II) Loading sub module "fbdevhw"
> [    23.511] (II) LoadModule: "fbdevhw"
> [    23.511] (II) Loading /usr/lib/xorg/modules/libfbdevhw.so
> [    23.511] (II) Module fbdevhw: vendor="X.Org Foundation"
> [    23.511]    compiled for 1.21.1.18, module version = 0.0.2
> [    23.511]    ABI class: X.Org Video Driver, version 25.2
> [    23.512] (II) modeset(0): Creating default Display subsection in
> Screen section
>          "Default Screen Section" for depth/fbbpp 24/32
> [    23.512] (==) modeset(0): Depth 24, (==) framebuffer bpp 32
> [    23.512] (==) modeset(0): RGB weight 888
> [    23.512] (==) modeset(0): Default visual is TrueColor
> ...
> [    23.911] (II) Loading sub module "fb"
> [    23.911] (II) LoadModule: "fb"
> [    23.911] (II) Module "fb" already built-in
> [    23.911] (II) UnloadModule: "fbdev"
> [    23.911] (II) Unloading fbdev
> [    23.912] (II) UnloadSubModule: "fbdevhw"
> [    23.912] (II) Unloading fbdevhw
> [    24.238] (==) modeset(0): Backing store enabled
> [    24.238] (==) modeset(0): Silken mouse enabled
> [    24.249] (II) modeset(0): Initializing kms color map for depth 24, 8
> bpc.
> [    24.250] (==) modeset(0): DPMS enabled
> [    24.250] (II) modeset(0): [DRI2] Setup complete
> [    24.250] (II) modeset(0): [DRI2]   DRI driver: kms_swrast
> [    24.250] (II) modeset(0): [DRI2]   VDPAU driver: kms_swrast
> ...
> [    24.770] (II) modeset(0): Disabling kernel dirty updates, not
> required.
> [    24.770] (EE) modeset(0): failed to set mode: Invalid argument
>
> xorg tries to use 24 and 32 bpp which pass on the fb API but which
> don't actually work on AMD KV260 when Xorg starts. As a workaround
> Xorg config can set color depth to 16 using /etc/X11/xorg.conf snippet:
>
> Section "Screen"
>          Identifier     "Default Screen"
>          Monitor        "Configured Monitor"
>          Device         "Configured Video Device"
>          DefaultDepth   16
> EndSection
>
> But this is cumbersome on images meant for multiple different arm64
> devices and boards. So instead set 16 bpp as preferred depth
> in zynqmp_kms fb driver which is used by Xorg in the logic to find
> out a working depth.
>
> Now Xorg startup and bpp query using fb API works and HDMI display
> shows graphics. /var/log/Xorg.0.log shows:
>
> [    23.219] (II) LoadModule: "fbdev"
> [    23.219] (II) Loading /usr/lib/xorg/modules/drivers/fbdev_drv.so
> [    23.219] (II) Module fbdev: vendor="X.Org Foundation"
> [    23.219]    compiled for 1.21.1.18, module version = 0.5.1
> [    23.219]    Module class: X.Org Video Driver
> [    23.219]    ABI class: X.Org Video Driver, version 25.2
> [    23.219] (II) modesetting: Driver for Modesetting Kernel Drivers:
> kms
> [    23.219] (II) FBDEV: driver for framebuffer: fbdev
> [    23.238] (II) modeset(0): using drv /dev/dri/card1
> [    23.238] (WW) Falling back to old probe method for fbdev
> [    23.238] (II) Loading sub module "fbdevhw"
> [    23.238] (II) LoadModule: "fbdevhw"
> [    23.239] (II) Loading /usr/lib/xorg/modules/libfbdevhw.so
> [    23.239] (II) Module fbdevhw: vendor="X.Org Foundation"
> [    23.239]    compiled for 1.21.1.18, module version = 0.0.2
> [    23.239]    ABI class: X.Org Video Driver, version 25.2
> [    23.240] (II) modeset(0): Creating default Display subsection in Screen section
>          "Default Screen Section" for depth/fbbpp 16/16
> [    23.240] (==) modeset(0): Depth 16, (==) framebuffer bpp 16
> [    23.240] (==) modeset(0): RGB weight 565
> [    23.240] (==) modeset(0): Default visual is TrueColor
> ...
> [    24.015] (==) modeset(0): Backing store enabled
> [    24.015] (==) modeset(0): Silken mouse enabled
> [    24.027] (II) modeset(0): Initializing kms color map for depth 16, 6 bpc.
> [    24.028] (==) modeset(0): DPMS enabled
> [    24.028] (II) modeset(0): [DRI2] Setup complete
> [    24.028] (II) modeset(0): [DRI2]   DRI driver: kms_swrast
> [    24.028] (II) modeset(0): [DRI2]   VDPAU driver: kms_swrast
>
> Cc: Bill Mills <bill.mills@...aro.org>
> Cc: Ilias Apalodimas <ilias.apalodimas@...aro.org>
> Cc: Anatoliy Klymenko <anatoliy.klymenko@....com>
> Cc: stable@...r.kernel.org
> Signed-off-by: Mikko Rapeli <mikko.rapeli@...aro.org>

Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>

> ---
>   drivers/gpu/drm/xlnx/zynqmp_kms.c | 1 +
>   1 file changed, 1 insertion(+)
>
> diff --git a/drivers/gpu/drm/xlnx/zynqmp_kms.c b/drivers/gpu/drm/xlnx/zynqmp_kms.c
> index ccc35cacd10cb..a42192c827af0 100644
> --- a/drivers/gpu/drm/xlnx/zynqmp_kms.c
> +++ b/drivers/gpu/drm/xlnx/zynqmp_kms.c
> @@ -506,6 +506,7 @@ int zynqmp_dpsub_drm_init(struct zynqmp_dpsub *dpsub)
>   	drm->mode_config.min_height = 0;
>   	drm->mode_config.max_width = ZYNQMP_DISP_MAX_WIDTH;
>   	drm->mode_config.max_height = ZYNQMP_DISP_MAX_HEIGHT;
> +	drm->mode_config.preferred_depth = 16;

There is another discussion on-going about rearranging planes. But to 
make user space work correctly, preferred_depth should be set no matter 
what.

Best regards
Thomas

>   
>   	ret = drm_vblank_init(drm, 1);
>   	if (ret)

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)