Hi Jason,
On 2021/9/28 19:57, Jason Gunthorpe wrote:
On Tue, Sep 28, 2021 at 07:30:41AM +0000, Tian, Kevin wrote:
Also, don't call it "hint", there is nothing hinty about this, it has
definitive functional impacts.
possibly dma_mode (too broad?) or dma_usage
You just need a flag to specify if the driver manages DMA ownership
itself, or if it requires the driver core to setup kernel ownership
DMA_OWNER_KERNEL
DMA_OWNER_DRIVER_CONTROLLED
?
There is a bool 'suprress_bind_attrs' already so it could be done like
this:
bool suppress_bind_attrs:1;
/* If set the driver must call iommu_XX as the first action in probe() */
bool suppress_dma_owner:1;
Which is pretty low cost.
Yes. Pretty low cost to fix the BUG_ON() issue. Any kernel-DMA driver
binding is blocked if the device's iommu group has been put into user-
dma mode.
Another issue is, when putting a device into user-dma mode, all devices
belonging to the same iommu group shouldn't be bound with a kernel-dma
driver. Kevin's prototype checks this by READ_ONCE(dev->driver). This is
not lock safe as discussed below,
https://lore.kernel.org/linux-iommu/20210927130935.GZ964074@xxxxxxxxxx/
Any guidance on this?
Best regards,
baolu
