Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755946AbaG3TgK (ORCPT ); Wed, 30 Jul 2014 15:36:10 -0400 Received: from bear.ext.ti.com ([192.94.94.41]:53149 "EHLO bear.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755766AbaG3TgI (ORCPT ); Wed, 30 Jul 2014 15:36:08 -0400 Message-ID: <53D948D4.6080603@ti.com> Date: Wed, 30 Jul 2014 15:34:44 -0400 From: Murali Karicheri User-Agent: Mozilla/5.0 (X11; Linux i686; rv:12.0) Gecko/20120430 Thunderbird/12.0.1 MIME-Version: 1.0 To: Jason Gunthorpe CC: Bjorn Helgaas , Richard Zhu , Marek Vasut , Randy Dunlap , Russell King , Pawel Moll , Arnd Bergmann , Ian Campbell , , Jingoo Han , , Kishon Vijay Abraham I , Rob Herring , Santosh Shilimkar , Kumar Gala , Grant Likely , Mark Rutland , Subject: Re: [PATCH v7 4/5] PCI: add PCI controller for keystone PCIe h/w References: <1405961925-27248-1-git-send-email-m-karicheri2@ti.com> <1405961925-27248-5-git-send-email-m-karicheri2@ti.com> <20140722223527.GA27965@google.com> <53CEEB1C.9020202@ti.com> <20140722235200.GC27965@google.com> <20140723174228.GB11270@obsidianresearch.com> In-Reply-To: <20140723174228.GB11270@obsidianresearch.com> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/23/2014 01:42 PM, Jason Gunthorpe wrote: > On Tue, Jul 22, 2014 at 05:52:00PM -0600, Bjorn Helgaas wrote: >> If there is a hardware defect, a PCI quirk is a reasonable way to work >> around it, since that's the main purpose of quirks. fixup_mpss_256() >> is an example of something that sounds superficially similar. > > It was my suggestion to engage the PCI-E tuning code. By my > understanding the HW bug is that read response segmentation at the > host bridge does not work - so all read requests from any downstream > device must have responses that fit within a single packet. > In the case of Keystone PCI, when I set the MRSS to 256 in the EP, PCI controller is able to function properly. Keystone spec says. ? Maximum outbound payload size of 128 bytes ? Maximum inbound payload size of 256 bytes ? Maximum remote read request size of 256 bytes I am interpreting the "Maximum remote read request size" to indicate it can's handle if it exceeds the limit. It has an outbound payload size of 128 bytes. So in this case a read request would results in 2 completion packets. So it seems to be able to segment up to maximum 256 bytes of read request. Where do I find the requirement in PCI spec that "read response segmentation at the host bridge does not work" ? > This is completely against how the spec envisions things working, > segmentation is a mandatory function. As you point out there is no > parameter bounding the maximum read request size that a completer will > accept. > > So, the only fix is that every downstream device must always have a > MRSS set to less than the MPS of the host bridge. Why this can't be the default behavior in the PCI core? Any cons? Murali > > Which means the tuning code must be involved somehow, as that code > controls the MRSS of unrelated devices... > > Regards, > Jason -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/