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Date:   Wed, 29 Apr 2020 09:05:39 +0530
From:   Srivatsa Vaddagiri <vatsa@codeaurora.org>
To:     "Michael S. Tsirkin" <mst@redhat.com>
Cc:     konrad.wilk@oracle.com, jasowang@redhat.com,
        jan.kiszka@siemens.com, will@kernel.org,
        stefano.stabellini@xilinx.com, iommu@lists.linux-foundation.org,
        virtualization@lists.linux-foundation.org,
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        pratikp@codeaurora.org, christoffer.dall@arm.com,
        alex.bennee@linaro.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 5/5] virtio: Add bounce DMA ops
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* Michael S. Tsirkin <mst@redhat.com> [2020-04-28 16:41:04]:

> > Won't we still need some changes to virtio to make use of its own pool (to
> > bounce buffers)? Something similar to its own DMA ops proposed in this patch?
> 
> If you are doing this for all devices, you need to either find a way
> to do this without chaning DMA ops, or by doing some automatic change
> to all drivers.

Ok thanks for this input. I will see how we can obfuscate this in DMA APIs
itself.

Can you also comment on the virtio transport problem I cited? The hypervisor we
are dealing with does not support MMIO transport. It supports message queue
send/recv and also doorbell, which I think can be used if we can make some
change like this to virtio_mmio.c:

+static inline u32
+virtio_readl(struct virtio_mmio_device *vm_dev, u32 reg_offset)
+{
+        return vm_dev->mmio_ops->readl(vm_dev, reg_offset);
+}
+ 
+static inline void
+virtio_writel(struct virtio_mmio_device *vm_dev, u32 reg_offset, u32 data)
+{
+        vm_dev->mmio_ops->writel(vm_dev, reg_offset, data);
+}


        /* Check magic value */
-        magic = readl(vm_dev->base + VIRTIO_MMIO_MAGIC_VALUE);
+        magic = vrito_readl(vm_dev, VIRTIO_MMIO_MAGIC_VALUE);

mmio_ops->readl on most platforms can default to readl itself, while on a
platform like us, it can boil down to message_queue send/recv. Would such a
change be acceptable?

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