linux-kernel - Re: [Xen-devel] [PATCH 3/8] drm/xen-front: fix 32-bit build warning

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Date:   Tue, 29 May 2018 08:58:58 +0300
From:   Oleksandr Andrushchenko <andr2000@...il.com>
To:     Arnd Bergmann <arnd@...db.de>,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>,
        David Airlie <airlied@...ux.ie>
Cc:     Daniel Vetter <daniel.vetter@...ll.ch>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        xen-devel@...ts.xen.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Dan Carpenter <dan.carpenter@...cle.com>
Subject: Re: [Xen-devel] [PATCH 3/8] drm/xen-front: fix 32-bit build warning

Hi,

On 05/25/2018 06:50 PM, Arnd Bergmann wrote:
> In 32-bit kernel builds, we cannot cast between a pointer and a 64-bit
> type:
>
> In file included from drivers/gpu/drm/xen/xen_drm_front_cfg.c:18:
> drivers/gpu/drm/xen/xen_drm_front.h: In function 'xen_drm_front_fb_to_cookie':
> drivers/gpu/drm/xen/xen_drm_front.h:129:9: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
>    return (u64)fb;
>
> drivers/gpu/drm/xen/xen_drm_front.h: In function 'xen_drm_front_dbuf_to_cookie':
> drivers/gpu/drm/xen/xen_drm_front.h:134:9: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
>    return (u64)gem_obj;
>
> drivers/gpu/drm/xen/xen_drm_front_shbuf.c: In function 'backend_unmap':
> drivers/gpu/drm/xen/xen_drm_front_shbuf.c:125:4: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
>     ((phys_addr_t)pfn_to_kaddr(page_to_xen_pfn(page)))
>
> Using uintptr_t instead probably does what we want here, although it's
> not clear to me why we assign a virtual address pointer to a phys_addr_t
> in backend_unmap().
>
> Fixes: c575b7eeb89f ("drm/xen-front: Add support for Xen PV display frontend")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>   drivers/gpu/drm/xen/xen_drm_front.h       | 4 ++--
>   drivers/gpu/drm/xen/xen_drm_front_shbuf.c | 2 +-
>   2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/xen/xen_drm_front.h b/drivers/gpu/drm/xen/xen_drm_front.h
> index 2c2479b571ae..5693b4a4b02b 100644
> --- a/drivers/gpu/drm/xen/xen_drm_front.h
> +++ b/drivers/gpu/drm/xen/xen_drm_front.h
> @@ -126,12 +126,12 @@ struct xen_drm_front_drm_info {
>   
>   static inline u64 xen_drm_front_fb_to_cookie(struct drm_framebuffer *fb)
>   {
> -	return (u64)fb;
> +	return (uintptr_t)fb;
>   }
>   
>   static inline u64 xen_drm_front_dbuf_to_cookie(struct drm_gem_object *gem_obj)
>   {
> -	return (u64)gem_obj;
> +	return (uintptr_t)gem_obj;
>   }
>   
>   int xen_drm_front_mode_set(struct xen_drm_front_drm_pipeline *pipeline,
> diff --git a/drivers/gpu/drm/xen/xen_drm_front_shbuf.c b/drivers/gpu/drm/xen/xen_drm_front_shbuf.c
> index 8099cb343ae3..d333b67cc1a0 100644
> --- a/drivers/gpu/drm/xen/xen_drm_front_shbuf.c
> +++ b/drivers/gpu/drm/xen/xen_drm_front_shbuf.c
> @@ -122,7 +122,7 @@ static void guest_calc_num_grefs(struct xen_drm_front_shbuf *buf)
>   }
>   
>   #define xen_page_to_vaddr(page) \
> -		((phys_addr_t)pfn_to_kaddr(page_to_xen_pfn(page)))
> +		((uintptr_t)pfn_to_kaddr(page_to_xen_pfn(page)))
>   
>   static int backend_unmap(struct xen_drm_front_shbuf *buf)
>   {
Thank you for your patch: this issue was already discussed [1] and 
applied [2] to
drm-misc-next.

Thank you,
Oleksandr

[1] https://patchwork.freedesktop.org/patch/224359/
[2] https://patchwork.freedesktop.org/patch/224920/