On Mon, Nov 16, 2020 at 09:19:50AM +0000, Christoph Hellwig wrote:
> I just noticed this showing up in Linus' tree and I'm not happy.
>
> This whole model of the DMA subdevices in remoteproc is simply broken.
>
> We really need to change the virtio code pass an expicit DMA device (
> similar to what e.g. the USB and RDMA code does),
Could you point me at an example or two please?
Thanks!
> instead of faking up
> devices with broken adhoc inheritance of DMA properties and magic poking
> into device parent relationships.
>
> Bjorn, I thought you were going to look into this a while ago?
>
>
> On Wed, Nov 04, 2020 at 03:31:36PM +0000, Alexander Lobakin wrote:
> > Since commit 086d08725d34 ("remoteproc: create vdev subdevice with
> > specific dma memory pool"), every remoteproc has a DMA subdevice
> > ("remoteprocX#vdevYbuffer") for each virtio device, which inherits
> > DMA capabilities from the corresponding platform device. This allowed
> > to associate different DMA pools with each vdev, and required from
> > virtio drivers to perform DMA operations with the parent device
> > (vdev->dev.parent) instead of grandparent (vdev->dev.parent->parent).
> >
> > virtio_rpmsg_bus was already changed in the same merge cycle with
> > commit d999b622fcfb ("rpmsg: virtio: allocate buffer from parent"),
> > but virtio_console did not. In fact, operations using the grandparent
> > worked fine while the grandparent was the platform device, but since
> > commit c774ad010873 ("remoteproc: Fix and restore the parenting
> > hierarchy for vdev") this was changed, and now the grandparent device
> > is the remoteproc device without any DMA capabilities.
> > So, starting v5.8-rc1 the following warning is observed:
> >
> > [ 2.483925] ------------[ cut here ]------------
> > [ 2.489148] WARNING: CPU: 3 PID: 101 at kernel/dma/mapping.c:427 0x80e7eee8
> > [ 2.489152] Modules linked in: virtio_console(+)
> > [ 2.503737] virtio_rpmsg_bus rpmsg_core
> > [ 2.508903]
> > [ 2.528898] <Other modules, stack and call trace here>
> > [ 2.913043]
> > [ 2.914907] ---[ end trace 93ac8746beab612c ]---
> > [ 2.920102] virtio-ports vport1p0: Error allocating inbufs
> >
> > kernel/dma/mapping.c:427 is:
> >
> > WARN_ON_ONCE(!dev->coherent_dma_mask);
> >
> > obviously because the grandparent now is remoteproc dev without any
> > DMA caps:
> >
> > [ 3.104943] Parent: remoteproc0#vdev1buffer, grandparent: remoteproc0
> >
> > Fix this the same way as it was for virtio_rpmsg_bus, using just the
> > parent device (vdev->dev.parent, "remoteprocX#vdevYbuffer") for DMA
> > operations.
> > This also allows now to reserve DMA pools/buffers for rproc serial
> > via Device Tree.
> >
> > Fixes: c774ad010873 ("remoteproc: Fix and restore the parenting hierarchy for vdev")
> > Cc: stable@xxxxxxxxxxxxxxx # 5.1+
> > Signed-off-by: Alexander Lobakin <alobakin@xxxxx>
> > ---
> > drivers/char/virtio_console.c | 8 ++++----
> > 1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> > index a2da8f768b94..1836cc56e357 100644
> > --- a/drivers/char/virtio_console.c
> > +++ b/drivers/char/virtio_console.c
> > @@ -435,12 +435,12 @@ static struct port_buffer *alloc_buf(struct virtio_device *vdev, size_t buf_size
> > /*
> > * Allocate DMA memory from ancestor. When a virtio
> > * device is created by remoteproc, the DMA memory is
> > - * associated with the grandparent device:
> > - * vdev => rproc => platform-dev.
> > + * associated with the parent device:
> > + * virtioY => remoteprocX#vdevYbuffer.
> > */
> > - if (!vdev->dev.parent || !vdev->dev.parent->parent)
> > + buf->dev = vdev->dev.parent;
> > + if (!buf->dev)
> > goto free_buf;
> > - buf->dev = vdev->dev.parent->parent;
> >
> > /* Increase device refcnt to avoid freeing it */
> > get_device(buf->dev);
> > --
> > 2.29.2
> >
> >
> ---end quoted text---
