linux-kernel - Re: [PATCH -next] drm/amdgpu: Use DIV_ROUND_UP_ULL instead of DIV_ROUND

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Message-ID: <5ffe00de-a7b6-3ac4-f61a-5f28b653e7b1@amd.com>
Date:   Thu, 10 Jun 2021 10:20:44 +0200
From:   Christian König <christian.koenig@....com>
To:     He Ying <heying24@...wei.com>, alexander.deucher@....com,
        Xinhui.Pan@....com, airlied@...ux.ie, daniel@...ll.ch,
        airlied@...hat.com, bskeggs@...hat.com, matthew.auld@...el.com,
        Ramesh.Errabolu@....com, mchehab+huawei@...nel.org,
        Dennis.Li@....com, funfunctor@...klore1984.net
Cc:     amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] drm/amdgpu: Use DIV_ROUND_UP_ULL instead of
 DIV_ROUND_UP



Am 10.06.21 um 10:20 schrieb He Ying:
> When compiling the kernel for MIPS with CONFIG_DRM_AMDGPU = y, errors are
> encountered as follows:
>
> drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.o: In function `amdgpu_vram_mgr_new':
> amdgpu_vram_mgr.c:(.text+0x740): undefined reference to `__udivdi3'
>
> Making a 64 bit division by a/b (a is uint64_t) is not supported by default
> in linux kernel space. Instead, using do_div is OK for this situation. For
> this problem, using DIV_ROUND_UP_ULL instead of DIV_ROUND_UP is better.

Already fixed by this patch in drm-next:

commit 691cf8cd7a531dbfcc29d09a23c509a86fd9b24f
Author: Dave Airlie <airlied@...hat.com>
Date:   Thu Jun 10 12:59:00 2021 +1000

     drm/amdgpu: use correct rounding macro for 64-bit

     This fixes 32-bit arm build due to lack of 64-bit divides.

Regards,
Christian.

>
> Fixes: 6a7f76e70fac ("drm/amdgpu: add VRAM manager v2")
> Reported-by: Hulk Robot <hulkci@...wei.com>
> Signed-off-by: He Ying <heying24@...wei.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
> index 9a6df02477ce..436ec246a7da 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
> @@ -407,7 +407,7 @@ static int amdgpu_vram_mgr_new(struct ttm_resource_manager *man,
>   #endif
>   		pages_per_node = max_t(uint32_t, pages_per_node,
>   				       tbo->page_alignment);
> -		num_nodes = DIV_ROUND_UP(PFN_UP(mem_bytes), pages_per_node);
> +		num_nodes = DIV_ROUND_UP_ULL(PFN_UP(mem_bytes), pages_per_node);
>   	}
>   
>   	node = kvmalloc(struct_size(node, mm_nodes, num_nodes),