On Mon, 10 Apr 2023 08:27:14 -0700, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
> On Mon, Apr 10, 2023 at 01:14:13PM +0800, Jason Wang wrote:
> > > But rethink, this is unreliable. Some platforms have returned their own ops,
> > > including X86.
> > >
> > > Because the priority of dev->dma_ops is higher than get_arch_dma_ops(), we
> > > should not let dev->dma_ops be null. We should define a set of dma_ops to
> > > actively implement direct dMA.
> >
> > Then this will duplicate with existing DMA API helpers. Could we tweak
> > the sparc or introduce a new flag for the device structure then the
> > DMA API knows it needs to use direct mapping?
> >
> > Adding Christoph for more comments.
>
> Code outside of the core kernel/dma/ code has no business doing
> anything with the dma_ops.
Do you mean we should not change the dma_ops from the outside of the core
kernel/dma/?
How about adding one new "dma_direct" to struct devive?
--- a/include/linux/dma-map-ops.h
+++ b/include/linux/dma-map-ops.h
@@ -88,6 +88,9 @@ struct dma_map_ops {
static inline const struct dma_map_ops *get_dma_ops(struct device *dev)
{
+ if (dev->dma_direct)
+ return NULL;
+
if (dev->dma_ops)
return dev->dma_ops;
return get_arch_dma_ops();
Thanks.
> WTF is going on?
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