linux-kernel - Re: [RFC PATCH] of/platform: Disable sysfb if a simple-framebuffer node is found

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Date:   Mon, 13 Nov 2023 10:18:16 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Javier Martinez Canillas <javierm@...hat.com>,
        linux-kernel@...r.kernel.org
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        Sima Vetter <daniel.vetter@...ll.ch>,
        Rob Herring <robh@...nel.org>, dri-devel@...ts.freedesktop.org,
        Andrew Worsley <amworsley@...il.com>,
        Hector Martin <marcan@...can.st>,
        Sergio Lopez <slp@...hat.com>,
        Frank Rowand <frowand.list@...il.com>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org
Subject: Re: [RFC PATCH] of/platform: Disable sysfb if a simple-framebuffer
 node is found



Am 13.11.23 um 09:51 schrieb Javier Martinez Canillas:
> Some DT platforms use EFI to boot and in this case the EFI Boot Services
> may register a EFI_GRAPHICS_OUTPUT_PROTOCOL handle, that will later be
> queried by the Linux EFI stub to fill the global struct screen_info data.
> 
> The data is used by the Generic System Framebuffers (sysfb) framework to
> add a platform device with platform data about the system framebuffer.
> 
> But if there is a "simple-framebuffer" node in the DT, the OF core will
> also do the same and add another device for the system framebuffer.
> 
> This could lead for example, to two platform devices ("simple-framebuffer"
> and "efi-framebuffer") to be added and matched with their corresponding
> drivers. So both efifb and simpledrm will be probed, leading to following:
> 
> [    0.055752] efifb: framebuffer at 0xbd58dc000, using 16000k, total 16000k
> [    0.055755] efifb: mode is 2560x1600x32, linelength=10240, pages=1
> [    0.055758] efifb: scrolling: redraw
> [    0.055759] efifb: Truecolor: size=2:10:10:10, shift=30:20:10:0
> ...
> [    3.295896] simple-framebuffer bd58dc000.framebuffer: [drm] *ERROR*
> could not acquire memory range [??? 0xffff79f30a29ee40-0x2a5000001a7
> flags 0x0]: -16
> [    3.298018] simple-framebuffer: probe of bd58dc000.framebuffer
> failed with error -16
> 
> To prevent the issue, make the OF core to disable sysfb if there is a node
> with a "simple-framebuffer" compatible. That way only this device will be
> registered and sysfb would not attempt to register another one using the
> screen_info data even if this has been filled.
> 
> This seems the correct thing to do in this case because:
> 
> a) On a DT platform, the DTB is the single source of truth since is what
>     describes the hardware topology. Even if EFI Boot Services are used to
>     boot the machine.
> 
> b) The of_platform_default_populate_init() function is called in the
>     arch_initcall_sync() initcall level while the sysfb_init() function
>     is called later in the subsys_initcall() initcall level.
> 
> Reported-by: Andrew Worsley <amworsley@...il.com>
> Closes: https://lore.kernel.org/all/20231111042926.52990-2-amworsley@gmail.com
> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>

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

> ---
> 
>   drivers/of/platform.c | 18 ++++++++++++++++--
>   1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/of/platform.c b/drivers/of/platform.c
> index f235ab55b91e..0a692fdfef59 100644
> --- a/drivers/of/platform.c
> +++ b/drivers/of/platform.c
> @@ -20,6 +20,7 @@
>   #include <linux/of_irq.h>
>   #include <linux/of_platform.h>
>   #include <linux/platform_device.h>
> +#include <linux/sysfb.h>
>   
>   #include "of_private.h"
>   
> @@ -621,8 +622,21 @@ static int __init of_platform_default_populate_init(void)
>   		}
>   
>   		node = of_get_compatible_child(of_chosen, "simple-framebuffer");
> -		of_platform_device_create(node, NULL, NULL);
> -		of_node_put(node);
> +		if (node) {
> +			/*
> +			 * Since a "simple-framebuffer" device is already added
> +			 * here, disable the Generic System Framebuffers (sysfb)
> +			 * to prevent it from registering another device for the
> +			 * system framebuffer later (e.g: using the screen_info
> +			 * data that may had been filled as well).
> +			 *
> +			 * This can happen for example on DT systems that do EFI
> +			 * booting and may provide a GOP handle to the EFI stub.
> +			 */
> +			sysfb_disable();
> +			of_platform_device_create(node, NULL, NULL);
> +			of_node_put(node);
> +		}
>   
>   		/* Populate everything else. */
>   		of_platform_default_populate(NULL, NULL, NULL);

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

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