Re: [PATCH rdma-next] RDMA: Explicitly pass in the dma_device to ib_register_device

From: Christoph Hellwig <hch@infradead.org>
To: Leon Romanovsky <leon@kernel.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 06:38:40 +0100	[thread overview]
Message-ID: <20200923053840.GA4809@infradead.org> (raw)
In-Reply-To: <20200922082745.2149973-1-leon@kernel.org>

> +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).

> +		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?