netdev - Re: [PATCH 1/7] media: videobuf-dma-contig: use dma_mmap

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Date:   Thu, 24 Nov 2022 15:10:43 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Christoph Hellwig <hch@....de>,
        Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Alexandra Winter <wintera@...ux.ibm.com>,
        Wenjia Zhang <wenjia@...ux.ibm.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Russell King <linux@...linux.org.uk>,
        Robin Murphy <robin.murphy@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-rdma@...r.kernel.org,
        iommu@...ts.linux.dev, linux-media@...r.kernel.org,
        netdev@...r.kernel.org, linux-s390@...r.kernel.org,
        alsa-devel@...a-project.org
Subject: Re: [PATCH 1/7] media: videobuf-dma-contig: use dma_mmap_coherent

Hi Christoph,

On 13/11/2022 17:35, Christoph Hellwig wrote:
> dma_alloc_coherent does not return a physical address, but a DMA address,
> which might be remapped or have an offset.  Passing the DMA address to
> vm_iomap_memory is thus broken.
> 
> Use the proper dma_mmap_coherent helper instead, and stop passing
> __GFP_COMP to dma_alloc_coherent, as the memory management inside the
> DMA allocator is hidden from the callers and does not require it.
> 
> With this the gfp_t argument to __videobuf_dc_alloc can be removed and
> hard coded to GFP_KERNEL.
> 
> Fixes: a8f3c203e19b ("[media] videobuf-dma-contig: add cache support")
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  drivers/media/v4l2-core/videobuf-dma-contig.c | 22 +++++++------------

Very, very old code :-) Hopefully in the not-too-distant future we can kill off
the old videobuf framework. But for now:

Acked-by: Hans Verkuil <hverkuil-cisco@...all.nl>

I assume you take this? If not, then let me know and I will pick it up for the media
subsystem.

Regards,

	Hans

>  1 file changed, 8 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/videobuf-dma-contig.c b/drivers/media/v4l2-core/videobuf-dma-contig.c
> index 52312ce2ba056..f2c4393595574 100644
> --- a/drivers/media/v4l2-core/videobuf-dma-contig.c
> +++ b/drivers/media/v4l2-core/videobuf-dma-contig.c
> @@ -36,12 +36,11 @@ struct videobuf_dma_contig_memory {
>  
>  static int __videobuf_dc_alloc(struct device *dev,
>  			       struct videobuf_dma_contig_memory *mem,
> -			       unsigned long size, gfp_t flags)
> +			       unsigned long size)
>  {
>  	mem->size = size;
> -	mem->vaddr = dma_alloc_coherent(dev, mem->size,
> -					&mem->dma_handle, flags);
> -
> +	mem->vaddr = dma_alloc_coherent(dev, mem->size, &mem->dma_handle,
> +					GFP_KERNEL);
>  	if (!mem->vaddr) {
>  		dev_err(dev, "memory alloc size %ld failed\n", mem->size);
>  		return -ENOMEM;
> @@ -258,8 +257,7 @@ static int __videobuf_iolock(struct videobuf_queue *q,
>  			return videobuf_dma_contig_user_get(mem, vb);
>  
>  		/* allocate memory for the read() method */
> -		if (__videobuf_dc_alloc(q->dev, mem, PAGE_ALIGN(vb->size),
> -					GFP_KERNEL))
> +		if (__videobuf_dc_alloc(q->dev, mem, PAGE_ALIGN(vb->size)))
>  			return -ENOMEM;
>  		break;
>  	case V4L2_MEMORY_OVERLAY:
> @@ -295,22 +293,18 @@ static int __videobuf_mmap_mapper(struct videobuf_queue *q,
>  	BUG_ON(!mem);
>  	MAGIC_CHECK(mem->magic, MAGIC_DC_MEM);
>  
> -	if (__videobuf_dc_alloc(q->dev, mem, PAGE_ALIGN(buf->bsize),
> -				GFP_KERNEL | __GFP_COMP))
> +	if (__videobuf_dc_alloc(q->dev, mem, PAGE_ALIGN(buf->bsize)))
>  		goto error;
>  
> -	/* Try to remap memory */
> -	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
> -
>  	/* the "vm_pgoff" is just used in v4l2 to find the
>  	 * corresponding buffer data structure which is allocated
>  	 * earlier and it does not mean the offset from the physical
>  	 * buffer start address as usual. So set it to 0 to pass
> -	 * the sanity check in vm_iomap_memory().
> +	 * the sanity check in dma_mmap_coherent().
>  	 */
>  	vma->vm_pgoff = 0;
> -
> -	retval = vm_iomap_memory(vma, mem->dma_handle, mem->size);
> +	retval = dma_mmap_coherent(q->dev, vma, mem->vaddr, mem->dma_handle,
> +				   mem->size);
>  	if (retval) {
>  		dev_err(q->dev, "mmap: remap failed with error %d. ",
>  			retval);