Re: [PATCH V2 3/4] misc: vop: simply return the saved dma address instead of virt_to_phys

[Christoph Hellwig <hch@infradead.org>]

On Tue, Sep 29, 2020 at 04:44:24PM +0800, Sherry Sun wrote:
> The device page and vring should use consistent memory which are
> allocated by dma_alloc_coherent api, when user space wants to get its
> physical address, virt_to_phys cannot be used, should simply return the
> saved device page dma address by get_dp_dma callback and the vring dma
> address saved in mic_vqconfig.

More importantly you can't just all virt_to_phys on a return value
from dma_alloc_coherent, so this needs to be folded into patch 1.

>  	if (!offset) {
> -		*pa = virt_to_phys(vpdev->hw_ops->get_dp(vpdev));
> +		if (vpdev->hw_ops->get_dp_dma)
> +			*pa = vpdev->hw_ops->get_dp_dma(vpdev);
> +		else {
> +			dev_err(vop_dev(vdev), "can't get device page physical address\n");
> +			return -EINVAL;
> +		}

I don't think we need the NULL check here.  Wouldn't it also make sense
to return the virtual and DMA address from ->get_dp instead of adding
another method?