[PATCH] video: simplefb: Map framebuffer region on probe on ARM64

[Sumit Garg]

Hi Luca,

On Wed, Mar 18, 2026 at 04:07:17PM +0100, Luca Weiss wrote:
> The framebuffer buffer might not be mapped on some devices.
> 
> This is #ifdef'ed for ARM64 since mmu_map_region() is not defined for
> any other architecture.

This isn't an appropriate fix to the problem.

> 
> Signed-off-by: Luca Weiss <luca.weiss at fairphone.com>
> ---
> Map 0x1000 extra due to unknown reason, but otherwise it's not enough
> and we still get a "Synchronous Abort" when drawing at the bottom of the
> framebuffer.
> 
> For milos-fairphone-fp6 the framebuffer is reg=0xe3940000
> size=0xa932c0 (2484*1116*4).
> 
> When just calling mmu_map_region with plat->size, then it's crashing at
> 0xe43d3000 even though everything up to 0xe43d32c0 should be mapped.
> With size+0x800 (or less) it was also still crashing, only size+0x1000
> then worked.
> 
> Possible I just don't know enough about memory mapping things, so
> suggestions welcome! :)

This sounds more likely the synchronous aborts caused by cache prefetch
of nearby reserved memory regions. I see there are some reserved mememory
regions around the address space you have mentioned on Milos.

On Qcom platforms, the default memory map strategy is to map the overall
DRAM space without excluding reserved reqions. One can exclude reserved
regions in a SoC specific manner here [1] but it adds some runtime
overhead. Give it a try for Milos as well in case it resolves your
issue.

I think we still need to revisit that reserved memory strategy where
default should rather be we unmap the reserved regions.

[1] https://github.com/u-boot/u-boot/blob/master/arch/arm/mach-snapdragon/board.c#L743

-Sumit

> ---
>  drivers/video/simplefb.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/video/simplefb.c b/drivers/video/simplefb.c
> index 8d0772d4e51..e144fde697b 100644
> --- a/drivers/video/simplefb.c
> +++ b/drivers/video/simplefb.c
> @@ -9,6 +9,7 @@
>  #include <log.h>
>  #include <video.h>
>  #include <asm/global_data.h>
> +#include <asm/system.h>
>  
>  static int simple_video_probe(struct udevice *dev)
>  {
> @@ -37,6 +38,11 @@ static int simple_video_probe(struct udevice *dev)
>  	plat->base = base;
>  	plat->size = size;
>  
> +#ifdef CONFIG_ARM64
> +	/* The framebuffer buffer might not be mapped on some devices */
> +	mmu_map_region((phys_addr_t)plat->base, (phys_addr_t)plat->size + 0x1000, false);
> +#endif
> +
>  	video_set_flush_dcache(dev, true);
>  
>  	debug("%s: Query resolution...\n", __func__);
> 
> ---
> base-commit: ba7bf918dafcd093ad733b07ba490baeb20cf5da
> change-id: 20260318-simplefb-map-abb9dba0eed1
> 
> Best regards,
> -- 
> Luca Weiss <luca.weiss at fairphone.com>
>