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

From: Bart Van Assche <bvanassche@acm.org>
To: Jason Gunthorpe <jgg@nvidia.com>, Christoph Hellwig <hch@infradead.org>
Cc: Leon Romanovsky <leon@kernel.org>,
	Doug Ledford <dledford@redhat.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: Tue, 6 Oct 2020 07:29:16 -0700	[thread overview]
Message-ID: <f20a4639-7674-8d2c-66dc-ebc028b14ef0@acm.org> (raw)
In-Reply-To: <20200924114940.GE9475@nvidia.com>

On 9/24/20 4:49 AM, Jason Gunthorpe wrote:
> On Thu, Sep 24, 2020 at 06:49:07AM +0100, Christoph Hellwig wrote:
>>>>> +	} 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.
>>>
>>> Inherit? This is overriding the PCI default of 64K to be 2G for RDMA
>>> devices.
>>
>> With inherit I mean the
>>
>> 		device->dev.dma_parms = dma_device->dma_parms;
>>
>> line, which is completely bogus.  All DMA mapping is done on the
>> dma_device in the RDMA core and ULPs, so it also can't have an effect.
> 
> Oh. Yes, no idea why that is there..
> 
> commit c9121262d57b8a3be4f08073546436ba0128ca6a
> Author: Bart Van Assche <bvanassche@acm.org>
> Date:   Fri Oct 25 15:58:30 2019 -0700
> 
>      RDMA/core: Set DMA parameters correctly
>      
>      The dma_set_max_seg_size() call in setup_dma_device() does not have any
>      effect since device->dev.dma_parms is NULL. Fix this by initializing
>      device->dev.dma_parms first.
> 
> Bart?

(just noticed this email)

Hi Jason,

That code may be a leftover from when the ib_dma_*() functions used &dev->dev as
their first argument instead of dev->dma_device. See also commit 0957c29f78af
("IB/core: Restore I/O MMU, s390 and powerpc support").

Bart.