netdev - Re: [EXTERNAL] Re: [PATCH 05/12] net: mana: Set the DMA device max page size

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Date:   Wed, 18 May 2022 13:05:25 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Ajay Sharma <sharmaajay@...rosoft.com>
Cc:     Long Li <longli@...rosoft.com>, KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Leon Romanovsky <leon@...nel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>
Subject: Re: [EXTERNAL] Re: [PATCH 05/12] net: mana: Set the DMA device max
 page size

On Wed, May 18, 2022 at 05:59:00AM +0000, Ajay Sharma wrote:
> Thanks Long. 
> Hello Jason,
> I am the author of the patch.
> To your comment below : 
> " As I've already said, you are supposed to set the value that limits to ib_sge and *NOT* the value that is related to ib_umem_find_best_pgsz. It is usually 2G because the ib_sge's typically work on a 32 bit length."
> 
> The ib_sge is limited by the __sg_alloc_table_from_pages() which
> uses ib_dma_max_seg_size() which is what is set by the eth driver
> using dma_set_max_seg_size() . Currently our hw does not support
> PTEs larger than 2M.

*sigh* again it has nothing to do with *PTEs* in the HW.

Jason