linux-kernel - Re: [Linaro-mm-sig] [PATCH 1/3] dma-buf: Introduce dma buffer sharing mechanism

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Date:	Wed, 25 Jan 2012 19:26:52 +0530
From:	"Semwal, Sumit" <sumit.semwal@...com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
	dri-devel@...ts.freedesktop.org, linux-media@...r.kernel.org,
	arnd@...db.de, airlied@...hat.com, linux@....linux.org.uk,
	patches@...aro.org, jesse.barker@...aro.org, daniel@...ll.ch
Subject: Re: [Linaro-mm-sig] [PATCH 1/3] dma-buf: Introduce dma buffer sharing mechanism

On Fri, Jan 20, 2012 at 6:53 PM, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
> Hi Summit,
>
> Sorry for the late review. I know that this code is now in mainline, but I
> still have a couple of comments. I'll send patches if you agree with them.
Hi Laurent,

Thanks for your review; apologies for being late in replying - I was
OoO for last couple of days.
>
> On Monday 26 December 2011 10:23:15 Sumit Semwal wrote:
<snip>
>>
>
> [snip]
>
>> diff --git a/drivers/base/dma-buf.c b/drivers/base/dma-buf.c
>> new file mode 100644
>> index 0000000..e38ad24
>> --- /dev/null
>> +++ b/drivers/base/dma-buf.c
>> @@ -0,0 +1,291 @@
>
> [snip]
>
>> +/**
>> + * dma_buf_export - Creates a new dma_buf, and associates an anon file
>> + * with this buffer, so it can be exported.
>> + * Also connect the allocator specific data and ops to the buffer.
>> + *
>> + * @priv:    [in]    Attach private data of allocator to this buffer
>> + * @ops:     [in]    Attach allocator-defined dma buf ops to the new buffer.
>> + * @size:    [in]    Size of the buffer
>> + * @flags:   [in]    mode flags for the file.
>> + *
>> + * Returns, on success, a newly created dma_buf object, which wraps the
>> + * supplied private data and operations for dma_buf_ops. On either missing
>> + * ops, or error in allocating struct dma_buf, will return negative error.
>> + *
>> + */
>> +struct dma_buf *dma_buf_export(void *priv, struct dma_buf_ops *ops,
>> +                             size_t size, int flags)
>> +{
>> +     struct dma_buf *dmabuf;
>> +     struct file *file;
>> +
>> +     if (WARN_ON(!priv || !ops
>> +                       || !ops->map_dma_buf
>> +                       || !ops->unmap_dma_buf
>> +                       || !ops->release)) {
>> +             return ERR_PTR(-EINVAL);
>> +     }
>> +
>> +     dmabuf = kzalloc(sizeof(struct dma_buf), GFP_KERNEL);
>> +     if (dmabuf == NULL)
>> +             return ERR_PTR(-ENOMEM);
>> +
>> +     dmabuf->priv = priv;
>> +     dmabuf->ops = ops;
>
> dmabuf->ops will never but NULL, but (see below)
>
<snip>
>> +struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
>> +                                       struct device *dev)
>> +{
>> +     struct dma_buf_attachment *attach;
>> +     int ret;
>> +
>> +     if (WARN_ON(!dmabuf || !dev || !dmabuf->ops))
>
> you still check dmabuf->ops here, as well as in several places below.
> Shouldn't these checks be removed ?
You're right - these can be removed.
>
>> +             return ERR_PTR(-EINVAL);
>> +
>> +     attach = kzalloc(sizeof(struct dma_buf_attachment), GFP_KERNEL);
>> +     if (attach == NULL)
>> +             goto err_alloc;
>
> What about returning ERR_PTR(-ENOMEM) directly here ?
>
Right; we can do that.
>> +
>> +     mutex_lock(&dmabuf->lock);
>> +
>> +     attach->dev = dev;
>> +     attach->dmabuf = dmabuf;
>
> These two lines can be moved before mutex_lock().
>
:) Yes - thanks for catching this.
<snip>
> --
> Regards,
>
> Laurent Pinchart

Let me know if you'd send patches for these, or should I just go ahead
and correct.

Best regards,
~Sumit.
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