linux-kernel - Re: [PATCH] vboxvideo: Fix incorrect type in assignment sparse warning

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Date:   Sat, 6 Jan 2018 17:00:56 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Alexander Kapshuk <alexander.kapshuk@...il.com>,
        gregkh@...uxfoundation.org, michael.thayer@...cle.com,
        dri-devel@...ts.freedesktop.org
Cc:     peda@...ntia.se, daniel.vetter@...ll.ch, cakturk@...il.com,
        seanpaul@...omium.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vboxvideo: Fix incorrect type in assignment sparse
 warning

Hi,

On 06-01-18 15:20, Alexander Kapshuk wrote:
> On Mon, Dec 25, 2017 at 04:42:59PM +0200, Alexander Kapshuk wrote:
>> Sparse emitted the following warning:
>> ../drivers/staging/vboxvideo/vbox_fb.c:173:27: warning: incorrect type in assignment (different address spaces)
>> ../drivers/staging/vboxvideo/vbox_fb.c:173:27:    expected char [noderef] <asn:2>*screen_base
>> ../drivers/staging/vboxvideo/vbox_fb.c:173:27:    got void *virtual
>>
>> The vbox_bo buffer object kernel mapping is handled by a call
>> to ttm_bo_kmap() prior to the assignment of bo->kmap.virtual to
>> info->screen_base of type char __iomem*.
>> Casting bo->kmap.virtual to char __iomem* in this assignment fixes
>> the warning.
>>
>> vboxvideo: Fix address space of expression removal sparse warning
>>
>> Sparse emitted the following warning:
>> ../drivers/staging/vboxvideo/vbox_main.c:64:25: warning: cast removes address space of expression
>>
>> vbox->vbva_buffers iomapping is handled by calling vbox_accel_init()
>> from vbox_hw_init().
>> __force attribute is used in assignment to vbva to fix the warning.
>>
>> Signed-off-by: Alexander Kapshuk <alexander.kapshuk@...il.com>
>> ---
>>   drivers/staging/vboxvideo/vbox_fb.c   | 2 +-
>>   drivers/staging/vboxvideo/vbox_main.c | 2 +-
>>   2 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/staging/vboxvideo/vbox_fb.c b/drivers/staging/vboxvideo/vbox_fb.c
>> index 8aed248db6e2..43c39eca4ae1 100644
>> --- a/drivers/staging/vboxvideo/vbox_fb.c
>> +++ b/drivers/staging/vboxvideo/vbox_fb.c
>> @@ -170,7 +170,7 @@ static int vboxfb_create(struct drm_fb_helper *helper,
>>   	drm_fb_helper_fill_var(info, &fbdev->helper, sizes->fb_width,
>>   			       sizes->fb_height);
>>
>> -	info->screen_base = bo->kmap.virtual;
>> +	info->screen_base = (char __iomem *)bo->kmap.virtual;
>>   	info->screen_size = size;
>>
>>   #ifdef CONFIG_DRM_KMS_FB_HELPER

This fix looks good to me.

>> diff --git a/drivers/staging/vboxvideo/vbox_main.c b/drivers/staging/vboxvideo/vbox_main.c
>> index 80bd039fa08e..973b3bcc04b1 100644
>> --- a/drivers/staging/vboxvideo/vbox_main.c
>> +++ b/drivers/staging/vboxvideo/vbox_main.c
>> @@ -61,7 +61,7 @@ void vbox_enable_accel(struct vbox_private *vbox)
>>   		if (vbox->vbva_info[i].vbva)
>>   			continue;
>>
>> -		vbva = (void *)vbox->vbva_buffers + i * VBVA_MIN_BUFFER_SIZE;
>> +		vbva = (void __force *)vbox->vbva_buffers + i * VBVA_MIN_BUFFER_SIZE;
>>   		if (!vbva_enable(&vbox->vbva_info[i],
>>   				 vbox->guest_pool, vbva, i)) {
>>   			/* very old host or driver error. */

Hmm, isn't there a cleaner way to fix this ? Maybe make vbva_enable's
argument (and the local vbva variable) of type u8 __iomem * too ?

Regards,

Hans