From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D4EADECE58E for ; Mon, 14 Oct 2019 13:51:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B138E207FF for ; Mon, 14 Oct 2019 13:51:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732267AbfJNNv3 (ORCPT ); Mon, 14 Oct 2019 09:51:29 -0400 Received: from relay9-d.mail.gandi.net ([217.70.183.199]:34401 "EHLO relay9-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730418AbfJNNv3 (ORCPT ); Mon, 14 Oct 2019 09:51:29 -0400 X-Originating-IP: 88.190.179.123 Received: from localhost (unknown [88.190.179.123]) (Authenticated sender: repk@triplefau.lt) by relay9-d.mail.gandi.net (Postfix) with ESMTPSA id 70DC2FF820; Mon, 14 Oct 2019 13:51:23 +0000 (UTC) Date: Mon, 14 Oct 2019 16:00:26 +0200 From: Remi Pommarel To: Marc Zyngier Cc: Lorenzo Pieralisi , Andrew Murray , Ellie Reeves , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, Bjorn Helgaas , Thomas Petazzoni , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v3] PCI: aardvark: Use LTSSM state to build link training flag Message-ID: <20191014140026.GB1426@voidbox> References: <20190522213351.21366-3-repk@triplefau.lt> <20190930154017.GF42880@e119886-lin.cambridge.arm.com> <20190930165230.GA12568@voidbox> <20191001080546.GI42880@e119886-lin.cambridge.arm.com> <20191013113415.3c653526@why> <20191014100129.GA18832@e121166-lin.cambridge.arm.com> <20191014130627.GA1426@voidbox> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.12.2 (2019-09-21) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 14, 2019 at 02:45:34PM +0100, Marc Zyngier wrote: > Hi Remi, > > On 2019-10-14 14:06, Remi Pommarel wrote: > > Hi Lorenzo, Marc, > > > > On Mon, Oct 14, 2019 at 11:01:29AM +0100, Lorenzo Pieralisi wrote: > > > On Sun, Oct 13, 2019 at 11:34:15AM +0100, Marc Zyngier wrote: > > > > On Tue, 1 Oct 2019 09:05:46 +0100 > > > > Andrew Murray wrote: > > > > > > > > Hi Lorenzo, > > > > > > > > > On Mon, Sep 30, 2019 at 06:52:30PM +0200, Remi Pommarel wrote: > > > > > > On Mon, Sep 30, 2019 at 04:40:18PM +0100, Andrew Murray wrote: > > > > > > > On Wed, May 22, 2019 at 11:33:51PM +0200, Remi Pommarel > > > wrote: > > > > > > > > Aardvark's PCI_EXP_LNKSTA_LT flag in its link status > > > register is not > > > > > > > > implemented and does not reflect the actual link training > > > state (the > > > > > > > > flag is always set to 0). In order to support link > > > re-training feature > > > > > > > > this flag has to be emulated. The Link Training and Status > > > State > > > > > > > > Machine (LTSSM) flag in Aardvark LMI config register could > > > be used as > > > > > > > > a link training indicator. Indeed if the LTSSM is in L0 or > > > upper state > > > > > > > > then link training has completed (see [1]). > > > > > > > > > > > > > > > > Unfortunately because after asking a link retraining it > > > takes a while > > > > > > > > for the LTSSM state to become less than 0x10 (due to L0s > > > to recovery > > > > > > > > state transition delays), LTSSM can still be in L0 while > > > link training > > > > > > > > has not finished yet. So this waits for link to be in > > > recovery or lesser > > > > > > > > state before returning after asking for a link retrain. > > > > > > > > > > > > > > > > [1] "PCI Express Base Specification", REV. 4.0 > > > > > > > > PCI Express, February 19 2014, Table 4-14 > > > > > > > > > > > > > > > > Signed-off-by: Remi Pommarel > > > > > > > > --- > > > > > > > > Changes since v1: > > > > > > > > - Rename retraining flag field > > > > > > > > - Fix DEVCTL register writing > > > > > > > > > > > > > > > > Changes since v2: > > > > > > > > - Rewrite patch logic so it is more legible > > > > > > > > > > > > > > > > Please note that I will unlikely be able to answer any > > > comments from May > > > > > > > > 24th to June 10th. > > > > > > > > --- > > > > > > > > drivers/pci/controller/pci-aardvark.c | 29 > > > ++++++++++++++++++++++++++- > > > > > > > > 1 file changed, 28 insertions(+), 1 deletion(-) > > > > > > > > > > > > > > > > diff --git a/drivers/pci/controller/pci-aardvark.c > > > b/drivers/pci/controller/pci-aardvark.c > > > > > > > > index 134e0306ff00..8803083b2174 100644 > > > > > > > > --- a/drivers/pci/controller/pci-aardvark.c > > > > > > > > +++ b/drivers/pci/controller/pci-aardvark.c > > > > > > > > @@ -180,6 +180,8 @@ > > > > > > > > #define LINK_WAIT_MAX_RETRIES 10 > > > > > > > > #define LINK_WAIT_USLEEP_MIN 90000 > > > > > > > > #define LINK_WAIT_USLEEP_MAX 100000 > > > > > > > > +#define RETRAIN_WAIT_MAX_RETRIES 10 > > > > > > > > +#define RETRAIN_WAIT_USLEEP_US 2000 > > > > > > > > > > > > > > > > #define MSI_IRQ_NUM 32 > > > > > > > > > > > > > > > > @@ -239,6 +241,17 @@ static int > > > advk_pcie_wait_for_link(struct advk_pcie *pcie) > > > > > > > > return -ETIMEDOUT; > > > > > > > > } > > > > > > > > > > > > > > > > +static void advk_pcie_wait_for_retrain(struct advk_pcie > > > *pcie) > > > > > > > > +{ > > > > > > > > + size_t retries; > > > > > > > > + > > > > > > > > + for (retries = 0; retries < RETRAIN_WAIT_MAX_RETRIES; > > > ++retries) { > > > > > > > > + if (!advk_pcie_link_up(pcie)) > > > > > > > > + break; > > > > > > > > + udelay(RETRAIN_WAIT_USLEEP_US); > > > > > > > > + } > > > > > > > > +} > > > > > > > > + > > > > > > > > static void advk_pcie_setup_hw(struct advk_pcie *pcie) > > > > > > > > { > > > > > > > > u32 reg; > > > > > > > > @@ -426,11 +439,20 @@ > > > advk_pci_bridge_emul_pcie_conf_read(struct pci_bridge_emul *bridge, > > > > > > > > return PCI_BRIDGE_EMUL_HANDLED; > > > > > > > > } > > > > > > > > > > > > > > > > + case PCI_EXP_LNKCTL: { > > > > > > > > + /* u32 contains both PCI_EXP_LNKCTL and PCI_EXP_LNKSTA > > > */ > > > > > > > > + u32 val = advk_readl(pcie, PCIE_CORE_PCIEXP_CAP + reg) > > > & > > > > > > > > + ~(PCI_EXP_LNKSTA_LT << 16); > > > > > > > > > > > > > > The commit message says "the flag is always set to 0" - > > > therefore I guess > > > > > > > you don't *need* to mask out the LT bit here? I assume this > > > is just > > > > > > > belt-and-braces but thought I'd check incase I've > > > misunderstood or if your > > > > > > > commit message is inaccurate. > > > > > > > > > > > > > > In any case masking out the bit (or adding a comment) makes > > > this code more > > > > > > > readable as the reader doesn't need to know what the > > > hardware does with this > > > > > > > bit. > > > > > > > > > > > > Actually vendor eventually responded that the bit was > > > reserved, but > > > > > > during my tests it remains to 0. > > > > > > > > > > > > So yes I am masking this out mainly for belt-and-braces and > > > legibility. > > > > > > > > > > Thanks for the clarification. > > > > > > > > > > > > > > > > > > > + if (!advk_pcie_link_up(pcie)) > > > > > > > > + val |= (PCI_EXP_LNKSTA_LT << 16); > > > > > > > > + *value = val; > > > > > > > > + return PCI_BRIDGE_EMUL_HANDLED; > > > > > > > > + } > > > > > > > > + > > > > > > > > case PCI_CAP_LIST_ID: > > > > > > > > case PCI_EXP_DEVCAP: > > > > > > > > case PCI_EXP_DEVCTL: > > > > > > > > case PCI_EXP_LNKCAP: > > > > > > > > - case PCI_EXP_LNKCTL: > > > > > > > > *value = advk_readl(pcie, PCIE_CORE_PCIEXP_CAP + reg); > > > > > > > > return PCI_BRIDGE_EMUL_HANDLED; > > > > > > > > default: > > > > > > > > @@ -447,8 +469,13 @@ > > > advk_pci_bridge_emul_pcie_conf_write(struct pci_bridge_emul *bridge, > > > > > > > > > > > > > > > > switch (reg) { > > > > > > > > case PCI_EXP_DEVCTL: > > > > > > > > + advk_writel(pcie, new, PCIE_CORE_PCIEXP_CAP + reg); > > > > > > > > + break; > > > > > > > > > > > > > > Why is this here? > > > > > > > > > > > > > > > > > > > Before PCI_EXP_DEVCTL and PCI_EXP_LNKCTL were doing the same > > > thing, but > > > > > > as now PCI_EXP_LNKCTL does extra things (i.e. wait for link to > > > > > > successfully retrain), they do have different behaviours. > > > > > > > > > > > > So this is here so PCI_EXP_DEVCTL keeps its old behaviour and > > > do not > > > > > > wait for link retrain in case an unrelated (PCI_EXP_LNKCTL_RL) > > > bit is > > > > > > set. > > > > > > > > > > Oh yes, of course! > > > > > > > > > > Thanks and: > > > > > > > > > > Reviewed-by: Andrew Murray > > > > > > > > Is there any hope for this workaround to make it into 5.4? > > > > > > > > My EspressoBin (which is blessed with this joke of a PCIe > > > controller) > > > > is pretty much a doorstop without it and dies with a SError early > > > at > > > > boot. > > > > > > > > FWIW: > > > > > > > > Tested-by: Marc Zyngier > > > > > > Hi Marc, > > > > > > First thing I will have to mark it as a Fixes: (if Remi can provide > > > me with a tag that'd be great), usually we send fixes at -rc* for > > > patches that fix code that went in the current (eg 5.4) material, > > > I will ask Bjorn to see if we can send this in one of the upcoming > > > -rc* even if it fixes older code. > > > > Sure, I think this could be considered a fix for the following commit : > > Fixes: 8a3ebd8de328 ("PCI: aardvark: Implement emulated root PCI > > bridge config space") > > > > Moreover, Marc, I am also a bit supprised that you did not have to use > > [1] to even be able to boot. > > No, I don't have that one, and yet the system boots fine (although PCI > doesn't get much use on this box). I guess I'm lucky... > > > Also if you want to be completely immune to this kind of SError (that > > could theoretically happen if the link goes down for other reasons than > > being retrained) you would have to use mainline ATF along with [2]. But > > the chances to hit that are low (could only happen in case of link > > errors). > > Now you've got me worried. Can you point me to that ATF patch? I'm quite > curious as to how you recover from an SError on a v8.0 CPU given that it > has no syndrome information and may as well signal "CPU on fire!"... > The patch is at [1]. Please note that this is done quite similarly for rcar. [1] https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/1541 -- Remi