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

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Date: Tue, 16 May 2023 09:58:19 +0200
From: Petr Tesařík <petr@...arici.cz>
To: Niklas Schnelle <schnelle@...ux.ibm.com>
Cc: Joerg Roedel <joro@...tes.org>, Matthew Rosato <mjrosato@...ux.ibm.com>,
 Will Deacon <will@...nel.org>, Wenjia Zhang <wenjia@...ux.ibm.com>, Robin
 Murphy <robin.murphy@....com>, Jason Gunthorpe <jgg@...pe.ca>, Gerd Bayer
 <gbayer@...ux.ibm.com>, Julian Ruess <julianr@...ux.ibm.com>, Pierre Morel
 <pmorel@...ux.ibm.com>, Alexandra Winter <wintera@...ux.ibm.com>, Heiko
 Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>, Alexander
 Gordeev <agordeev@...ux.ibm.com>, Christian Borntraeger
 <borntraeger@...ux.ibm.com>, Sven Schnelle <svens@...ux.ibm.com>, Suravee
 Suthikulpanit <suravee.suthikulpanit@....com>, Hector Martin
 <marcan@...can.st>, Sven Peter <sven@...npeter.dev>, Alyssa Rosenzweig
 <alyssa@...enzweig.io>, David Woodhouse <dwmw2@...radead.org>, Lu Baolu
 <baolu.lu@...ux.intel.com>, Andy Gross <agross@...nel.org>, Bjorn Andersson
 <andersson@...nel.org>, Konrad Dybcio <konrad.dybcio@...aro.org>, Yong Wu
 <yong.wu@...iatek.com>, Matthias Brugger <matthias.bgg@...il.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 Gerald Schaefer <gerald.schaefer@...ux.ibm.com>, Orson Zhai
 <orsonzhai@...il.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>, Chunyan
 Zhang <zhang.lyra@...il.com>, Chen-Yu Tsai <wens@...e.org>, Jernej Skrabec
 <jernej.skrabec@...il.com>, Samuel Holland <samuel@...lland.org>, Thierry
 Reding <thierry.reding@...il.com>, Krishna Reddy <vdumpa@...dia.com>,
 Jonathan Hunter <jonathanh@...dia.com>, Jonathan Corbet <corbet@....net>,
 linux-s390@...r.kernel.org, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, iommu@...ts.linux.dev, asahi@...ts.linux.dev,
 linux-arm-kernel@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
 linux-mediatek@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
 linux-tegra@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v9 1/6] s390/ism: Set DMA coherent mask

On Mon, 15 May 2023 11:15:51 +0200
Niklas Schnelle <schnelle@...ux.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@...ux.ibm.com>
> Reviewed-by: Matthew Rosato <mjrosato@...ux.ibm.com>
> Signed-off-by: Niklas Schnelle <schnelle@...ux.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