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Date:   Fri, 23 Oct 2020 10:28:37 +0100
From:   Christoph Hellwig <hch@infradead.org>
To:     Sherry Sun <sherry.sun@nxp.com>
Cc:     hch@infradead.org, sudeep.dutt@intel.com, ashutosh.dixit@intel.com,
        arnd@arndb.de, gregkh@linuxfoundation.org, kishon@ti.com,
        lorenzo.pieralisi@arm.com, linux-kernel@vger.kernel.org,
        linux-pci@vger.kernel.org, linux-imx@nxp.com
Subject: Re: [PATCH V3 4/4] misc: vop: mapping kernel memory to user space as
 noncached
Message-ID: <20201023092837.GC29066@infradead.org>
References: <20201022050638.29641-1-sherry.sun@nxp.com>
 <20201022050638.29641-5-sherry.sun@nxp.com>
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On Thu, Oct 22, 2020 at 01:06:38PM +0800, Sherry Sun wrote:
> Mapping kernel space memory to user space as noncached, since user space
> need check the updates of avail_idx and device page flags timely.
> 
> Signed-off-by: Joakim Zhang <qiangqing.zhang@nxp.com>
> Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
> ---
>  drivers/misc/mic/vop/vop_vringh.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/misc/mic/vop/vop_vringh.c b/drivers/misc/mic/vop/vop_vringh.c
> index b5612183dcb8..b75c2b713a3b 100644
> --- a/drivers/misc/mic/vop/vop_vringh.c
> +++ b/drivers/misc/mic/vop/vop_vringh.c
> @@ -1058,7 +1058,7 @@ static int vop_mmap(struct file *f, struct vm_area_struct *vma)
>  		}
>  		err = remap_pfn_range(vma, vma->vm_start + offset,
>  				      pa >> PAGE_SHIFT, size,
> -				      vma->vm_page_prot);
> +				      pgprot_noncached(vma->vm_page_prot));

Again, memory allocated using dma_alloc_coherent can only be mapped
using dma_mmap_coherent, which will use the right attributes for the
mapping, which often are cached.