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[142.162.113.180]) by smtp.gmail.com with ESMTPSA id v137sm396839qka.64.2019.10.30.11.07.55 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 30 Oct 2019 11:07:55 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1iPsNu-00013G-Oj; Wed, 30 Oct 2019 15:07:54 -0300 Date: Wed, 30 Oct 2019 15:07:54 -0300 From: Jason Gunthorpe To: "Marciniszyn, Mike" Cc: "Dalessandro, Dennis" , "dledford@redhat.com" , "linux-rdma@vger.kernel.org" , "Wan, Kaike" , "stable@vger.kernel.org" , "Erwin, James" Subject: Re: [PATCH for-rc 1/4] IB/hfi1: Allow for all speeds higher than gen3 Message-ID: <20191030180754.GA31799@ziepe.ca> References: <20191025161717.106825.14421.stgit@awfm-01.aw.intel.com> <20191025195823.106825.63080.stgit@awfm-01.aw.intel.com> <20191029195214.GA1802@ziepe.ca> <32E1700B9017364D9B60AED9960492BC729594E1@fmsmsx120.amr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <32E1700B9017364D9B60AED9960492BC729594E1@fmsmsx120.amr.corp.intel.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-rdma-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org On Tue, Oct 29, 2019 at 09:19:34PM +0000, Marciniszyn, Mike wrote: > > Subject: Re: [PATCH for-rc 1/4] IB/hfi1: Allow for all speeds higher than gen3 > > > > On Fri, Oct 25, 2019 at 03:58:24PM -0400, Dennis Dalessandro wrote: > > > From: James Erwin > > > > > > The driver avoids the gen3 speed bump when the parent > > > bus speed isn't identical to gen3, 8.0GT/s. This is not > > > compatible with gen4 and newer speeds. > > > > > > Fix by relaxing the test to explicitly look for the lower > > > capability speeds which inherently allows for all future speeds. > > > > This description does not seem like stable material to me. > > > > Having a card unknowingly operate at half speed would seem pretty serious to me. Since gen4 systems are really new this also sounds like a new feature to me.. You need to be concerned that changing the pci setup doesn't cause regressions on existing systems too. > Perhaps the description should say: > > IB/hfi1: Insure full Gen3 speed in a Gen4 system And maybe explain what the actual user visible impact is here. Sounds like plugging a card into a gen4 system will not run at gen3 speeds? Jason