Re: [PATCH v9 1/6] s390/ism: Set DMA coherent mask

[Petr Tesařík]

On Mon, 15 May 2023 11:15:51 +0200
Niklas Schnelle <schnelle@xxxxxxxxxxxxx> wrote:

> A future change will convert the DMA API implementation from the
> architecture specific arch/s390/pci/pci_dma.c to using the common code
> drivers/iommu/dma-iommu.c which the utilizes the same IOMMU hardware
> through the s390-iommu driver. Unlike the s390 specific DMA API this
> requires devices to correctly call set the coherent mask to be allowed
> to use IOVAs >2^32 in dma_alloc_coherent(). This was however not done
> for ISM devices. ISM requires such addresses since currently the DMA
> aperture for PCI devices starts at 2^32 and all calls to
> dma_alloc_coherent() would thus fail.
> 
> Reviewed-by: Alexandra Winter <wintera@xxxxxxxxxxxxx>
> Reviewed-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxx>
> Signed-off-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
> ---
>  drivers/s390/net/ism_drv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/s390/net/ism_drv.c b/drivers/s390/net/ism_drv.c
> index 8acb9eba691b..1399b5dc646c 100644
> --- a/drivers/s390/net/ism_drv.c
> +++ b/drivers/s390/net/ism_drv.c
> @@ -660,7 +660,7 @@ static int ism_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>  	if (ret)
>  		goto err_disable;
>  
> -	ret = dma_set_mask(&pdev->dev, DMA_BIT_MASK(64));
> +	ret = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64));

Ah. I love this change. I have already wondered a few times if the
coherent DMA mask for this device may actually be different from
dma_mask. Now I know. ;-)

Thanks!

Petr T