Hi Amit and Rusty,
I've been looking into the possibility of using the Virtio Console
Driver together with the remoteproc framework to communicate with
ST-Ericsson modem over shared memory.
It seems like Virtio Console would be a good fit, except for a issue
with buffer allocation. Due to HW limitations the STE-Modem cannot
access kernel memory (no IOMMU and limited address range). Instead
we have a designated shared memory region used for IPC.
Due to this I cannot use kmalloc() for buffer allocation, but I
have to allocate buffers from the memory region shared with the
modem.
In remoteproc this is solved by using dma_alloc_coherent() for all
memory to be shared with the modem. This works fine for me, because
I can pass the IPC memory region to dma_declare_coherent_memory()
so dma_alloc_coherent() will allocate from this memory region.
I think I can solve this issue in Virtio Console by changing calls
to kmalloc() to something like:
if (virtio_has_feature(vdev, VIRTIO_CONSOLE_USE_DMA_MEM)) {
dma_addr_t dma;
buf = dma_alloc_coherent(dev, size, &dma, GFP_KERNEL);
} else
buf = kmalloc(count, GFP_KERNEL);
I'd like to get the opinion from you virtualization folks on this!
If you think it looks reasonable I might start cooking some patches...
Regards,
Sjur
On Fri, Jun 1, 2012 at 10:31 AM, Sjur BRENDELAND <sjur.brandeland at stericsson.com> wrote:> ? ? ? ?if (virtio_has_feature(vdev, VIRTIO_CONSOLE_USE_DMA_MEM)) { > ? ? ? ? ? ? ? ?dma_addr_t dma; > ? ? ? ? ? ? ? ?buf = dma_alloc_coherent(dev, size, &dma, GFP_KERNEL); > ? ? ? ?} else > ? ? ? ? ? ? ? ?buf = kmalloc(count, GFP_KERNEL);Something along those lines is also needed for remote processors which access memory via an IOMMU (e.g. OMAP4's M3 and DSP). Allocating the memory via the DMA API will seamlessly configure the relevant IOMMU as needed, and will make the buffers accessible to the remote processors. Thanks, Ohad.
Hi Sjur, On (Fri) 01 Jun 2012 [09:31:30], Sjur BRENDELAND wrote:> Hi Amit and Rusty, > > I've been looking into the possibility of using the Virtio Console > Driver together with the remoteproc framework to communicate with > ST-Ericsson modem over shared memory. > > It seems like Virtio Console would be a good fit, except for a issue > with buffer allocation. Due to HW limitations the STE-Modem cannot > access kernel memory (no IOMMU and limited address range). Instead > we have a designated shared memory region used for IPC. > > Due to this I cannot use kmalloc() for buffer allocation, but I > have to allocate buffers from the memory region shared with the > modem. > > In remoteproc this is solved by using dma_alloc_coherent() for all > memory to be shared with the modem. This works fine for me, because > I can pass the IPC memory region to dma_declare_coherent_memory() > so dma_alloc_coherent() will allocate from this memory region. > > I think I can solve this issue in Virtio Console by changing calls > to kmalloc() to something like: > > if (virtio_has_feature(vdev, VIRTIO_CONSOLE_USE_DMA_MEM)) { > dma_addr_t dma; > buf = dma_alloc_coherent(dev, size, &dma, GFP_KERNEL); > } else > buf = kmalloc(count, GFP_KERNEL); > > I'd like to get the opinion from you virtualization folks on this! > If you think it looks reasonable I might start cooking some patches...I don't have a problem with this. Thanks, Amit