On Wed, Sep 23, 2020 at 06:38:40AM +0100, Christoph Hellwig wrote:
> > +static void setup_dma_device(struct ib_device *device,
> > + struct device *dma_device)
> > {
> > + if (!dma_device) {
> > /*
> > + * If the caller does not provide a DMA capable device then the
> > + * IB device will be used. In this case the caller should fully
> > + * setup the ibdev for DMA. This usually means using
> > + * dma_virt_ops.
> > */
> > +#ifdef CONFIG_DMA_OPS
> > + if (WARN_ON(!device->dev.dma_ops))
> > + return;
> > +#endif
>
> dma ops are entirely optiona and NULL for the most common case
> (direct mapping without an IOMMU).
IMHO we don't support such mode (without IOMMU).
>
> > + if (WARN_ON(!device->dev.dma_parms))
> > + return;
> > +
> > + dma_device = &device->dev;
> > + } else {
> > + device->dev.dma_parms = dma_device->dma_parms;
> > /*
> > + * Auto setup the segment size if a DMA device was passed in.
> > + * The PCI core sets the maximum segment size to 64 KB. Increase
> > + * this parameter to 2 GB.
> > */
> > + dma_set_max_seg_size(dma_device, SZ_2G);
>
> You can't just inherity DMA properties like this this. Please
> fix all code that looks at the seg size to look at the DMA device.
>
> Btw, where does the magic 2G come from?
It comes from patch d10bcf947a3e ("RDMA/umem: Combine contiguous
PAGE_SIZE regions in SGEs"), I can't say about all devices, but this is
the limit for mlx5, rxe and SIW devices.
Thanks
