linux-kernel - Re: [PATCH 1/2] drm: fix drm

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Message-ID: <20170111162713.veyyu56sbjaym3fe@phenom.ffwll.local>
Date:   Wed, 11 Jan 2017 17:27:13 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Daniel Vetter <daniel.vetter@...ll.ch>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Sean Paul <seanpaul@...omium.org>,
        David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] drm: fix drm_vm for NOMMU builds

On Wed, Jan 11, 2017 at 02:33:34PM +0100, Arnd Bergmann wrote:
> When building DRM without an MMU, we run into a compile-time error because
> pte_wrprotect() is not defined:
> 
> drivers/gpu/drm/drm_vm.c: In function 'drm_mmap_dma':
> drivers/gpu/drm/drm_vm.c:496:9: error: implicit declaration of function 'pte_wrprotect' [-Werror=implicit-function-declaration]
> 
> The line is not meaningful here, so we can simply add another
> compile-time check around it.
> 
> Fixes: 62a0d98a188c ("drm: allow to use mmuless SoC")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

We don't need drm_vm.c on modern drivers, and the idea was to simply not
compile it when not needed. See:

commit 99c48e1e38f0aeaa107ad67c8d91f6c9d9d567a9
Author: Benjamin Gaignard <benjamin.gaignard@...aro.org>
Date:   Wed Jan 4 10:12:56 2017 +0100

    drm: compile drm_vm.c only when needed


How did you manage to enable this stuff?
-Daniel

> ---
>  drivers/gpu/drm/drm_vm.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_vm.c b/drivers/gpu/drm/drm_vm.c
> index bd311c77c254..038946588ed7 100644
> --- a/drivers/gpu/drm/drm_vm.c
> +++ b/drivers/gpu/drm/drm_vm.c
> @@ -488,7 +488,7 @@ static int drm_mmap_dma(struct file *filp, struct vm_area_struct *vma)
>  		vma->vm_flags &= ~(VM_WRITE | VM_MAYWRITE);
>  #if defined(__i386__) || defined(__x86_64__)
>  		pgprot_val(vma->vm_page_prot) &= ~_PAGE_RW;
> -#else
> +#elif IS_ENABLED(CONFIG_MMU)
>  		/* Ye gads this is ugly.  With more thought
>  		   we could move this up higher and use
>  		   `protection_map' instead.  */
> @@ -572,7 +572,7 @@ static int drm_mmap_locked(struct file *filp, struct vm_area_struct *vma)
>  		vma->vm_flags &= ~(VM_WRITE | VM_MAYWRITE);
>  #if defined(__i386__) || defined(__x86_64__)
>  		pgprot_val(vma->vm_page_prot) &= ~_PAGE_RW;
> -#else
> +#elif defined (CONFIG_MMU)
>  		/* Ye gads this is ugly.  With more thought
>  		   we could move this up higher and use
>  		   `protection_map' instead.  */
> -- 
> 2.9.0
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch