On Mon, Sep 03, 2012 at 04:57:45PM +0200, Sjur Brændeland wrote:
> Hi Michael,
>
> > How does access to descriptors work in this setup?
>
> When the ring is setup by remoteproc the descriptors are
> also allocated using dma_alloc_coherent().
>
> >> -static void free_buf(struct port_buffer *buf)
> >> +/* Allcoate data buffer from DMA memory if requested */
> >
> > typo
>
> Thanks.
>
> >> +static inline void *
> >> +alloc_databuf(struct virtio_device *vdev, size_t size, dma_addr_t *dma_handle,
> >> + gfp_t flag)
> >> {
> >> - kfree(buf->buf);
> >> +#ifdef CONFIG_HAS_DMA
> >> + if (virtio_has_feature(vdev, VIRTIO_CONSOLE_F_DMA_MEM)) {
> >> + struct device *dev = &vdev->dev;
> >> + /*
> >> + * Allocate DMA memory from ancestors. Finding the ancestor
> >> + * is a bit quirky when DMA_MEMORY_INCLUDES_CHILDREN is not
> >> + * implemented.
> >> + */
> >> + dev = dev->parent ? dev->parent : dev;
> >> + dev = dev->parent ? dev->parent : dev;
> >> + return dma_alloc_coherent(dev, size, dma_handle, flag);
> >> + }
> >> +#endif
> >
> > Are these ifdefs really needed? If DMA_MEM is set,
> > can't we use dma_alloc_coherent
> > unconditionally?
>
> If an architecture do not support DMA you will get
> a link error: "unknown symbol" for dma_alloc_coherent.
>
> Regards,
> Sjur
Yes, it even seems intentional.
But I have a question: can the device work without DMA?
Does not VIRTIO_CONSOLE_F_DMA_MEM mean dma api is required?
If yes you should just fail load.
Also let's add a wrapper at top of file so ifdefs
do not litter the code like this. For example:
#ifdef CONFIG_HAS_DMA
#define VIRTIO_CONSOLE_HAS_DMA (1)
#else
#define VIRTIO_CONSOLE_HAS_DMA (0)
#endif
Now use if instead of ifdef.
--
MST
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