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From: Leon Romanovsky <leon@kernel.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: Doug Ledford <dledford@redhat.com>,
	Jason Gunthorpe <jgg@nvidia.com>,
	Adit Ranadive <aditr@vmware.com>,
	Ariel Elior <aelior@marvell.com>,
	Bernard Metzler <bmt@zurich.ibm.com>,
	Christian Benvenuti <benve@cisco.com>,
	Dennis Dalessandro <dennis.dalessandro@intel.com>,
	Devesh Sharma <devesh.sharma@broadcom.com>,
	Faisal Latif <faisal.latif@intel.com>,
	Gal Pressman <galpress@amazon.com>, Lijun Ou <oulijun@huawei.com>,
	linux-rdma@vger.kernel.org,
	Michal Kalderon <mkalderon@marvell.com>,
	Mike Marciniszyn <mike.marciniszyn@intel.com>,
	Naresh Kumar PBS <nareshkumar.pbs@broadcom.com>,
	Nelson Escobar <neescoba@cisco.com>,
	Parav Pandit <parav@nvidia.com>,
	Parvi Kaustubhi <pkaustub@cisco.com>,
	Potnuri Bharat Teja <bharat@chelsio.com>,
	Selvin Xavier <selvin.xavier@broadcom.com>,
	Shiraz Saleem <shiraz.saleem@intel.com>,
	Somnath Kotur <somnath.kotur@broadcom.com>,
	Sriharsha Basavapatna <sriharsha.basavapatna@broadcom.com>,
	VMware PV-Drivers <pv-drivers@vmware.com>,
	Weihang Li <liweihang@huawei.com>,
	"Wei Hu(Xavier)" <huwei87@hisilicon.com>,
	Yishai Hadas <yishaih@nvidia.com>,
	Zhu Yanjun <yanjunz@nvidia.com>
Subject: Re: [PATCH rdma-next] RDMA: Explicitly pass in the dma_device to ib_register_device
Date: Wed, 23 Sep 2020 09:45:52 +0300	[thread overview]
Message-ID: <20200923064552.GG1223944@unreal> (raw)
In-Reply-To: <20200923053840.GA4809@infradead.org>

On Wed, Sep 23, 2020 at 06:38:40AM +0100, Christoph Hellwig wrote:
> > +static void setup_dma_device(struct ib_device *device,
> > +			     struct device *dma_device)
> >  {
> > +	if (!dma_device) {
> >  		/*
> > +		 * If the caller does not provide a DMA capable device then the
> > +		 * IB device will be used. In this case the caller should fully
> > +		 * setup the ibdev for DMA. This usually means using
> > +		 * dma_virt_ops.
> >  		 */
> > +#ifdef CONFIG_DMA_OPS
> > +		if (WARN_ON(!device->dev.dma_ops))
> > +			return;
> > +#endif
>
> dma ops are entirely optiona and NULL for the most common case
> (direct mapping without an IOMMU).

IMHO we don't support such mode (without IOMMU).

>
> > +		if (WARN_ON(!device->dev.dma_parms))
> > +			return;
> > +
> > +		dma_device = &device->dev;
> > +	} else {
> > +		device->dev.dma_parms = dma_device->dma_parms;
> >  		/*
> > +		 * Auto setup the segment size if a DMA device was passed in.
> > +		 * The PCI core sets the maximum segment size to 64 KB. Increase
> > +		 * this parameter to 2 GB.
> >  		 */
> > +		dma_set_max_seg_size(dma_device, SZ_2G);
>
> You can't just inherity DMA properties like this this.  Please
> fix all code that looks at the seg size to look at the DMA device.
>
> Btw, where does the magic 2G come from?

It comes from patch d10bcf947a3e ("RDMA/umem: Combine contiguous
PAGE_SIZE regions in SGEs"), I can't say about all devices, but this is
the limit for mlx5, rxe and SIW devices.

Thanks

  reply	other threads:[~2020-09-23  6:45 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-22  8:27 [PATCH rdma-next] RDMA: Explicitly pass in the dma_device to ib_register_device Leon Romanovsky
2020-09-22  8:58 ` Bernard Metzler
2020-09-22 10:14   ` Leon Romanovsky
2020-09-22 14:22   ` Bernard Metzler
2020-09-22 16:22     ` Jason Gunthorpe
2020-09-23  5:39       ` Christoph Hellwig
2020-09-23 18:35         ` Jason Gunthorpe
2020-09-24  5:53           ` Christoph Hellwig
2020-09-24  6:13             ` Christoph Hellwig
2020-09-24 11:55               ` Jason Gunthorpe
2020-09-24  7:31             ` Parav Pandit
2020-09-23  5:38 ` Christoph Hellwig
2020-09-23  6:45   ` Leon Romanovsky [this message]
2020-09-23  6:54     ` Christoph Hellwig
2020-09-23  7:10       ` Leon Romanovsky
2020-09-23  7:21         ` Christoph Hellwig
2020-09-23 18:34   ` Jason Gunthorpe
2020-09-24  5:49     ` Christoph Hellwig
2020-09-24 11:49       ` Jason Gunthorpe
2020-10-06 14:29         ` Bart Van Assche
2020-10-06 16:53           ` Jason Gunthorpe
2020-10-06 18:22             ` Bart Van Assche
2020-10-06 18:39               ` Jason Gunthorpe

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