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Date:   Tue, 16 May 2023 09:58:19 +0200
From:   Petr =?UTF-8?B?VGVzYcWZw61r?= <petr@tesarici.cz>
To:     Niklas Schnelle <schnelle@linux.ibm.com>
Cc:     Joerg Roedel <joro@8bytes.org>,
        Matthew Rosato <mjrosato@linux.ibm.com>,
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Subject: Re: [PATCH v9 1/6] s390/ism: Set DMA coherent mask
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        <20230310-dma_iommu-v9-1-65bb8edd2beb@linux.ibm.com>
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On Mon, 15 May 2023 11:15:51 +0200
Niklas Schnelle <schnelle@linux.ibm.com> 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@linux.ibm.com>
> Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
> Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
> ---
>  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