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[209.132.180.67]) by mx.google.com with ESMTP id e22si34741160pgi.66.2019.04.30.04.35.34; Tue, 30 Apr 2019 04:35:52 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727254AbfD3Lef (ORCPT + 99 others); Tue, 30 Apr 2019 07:34:35 -0400 Received: from foss.arm.com ([217.140.101.70]:45112 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726129AbfD3Lef (ORCPT ); Tue, 30 Apr 2019 07:34:35 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 75CEE80D; Tue, 30 Apr 2019 04:34:34 -0700 (PDT) Received: from e121166-lin.cambridge.arm.com (e121166-lin.cambridge.arm.com [10.1.196.255]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0F5693F5C1; Tue, 30 Apr 2019 04:34:32 -0700 (PDT) Date: Tue, 30 Apr 2019 12:34:27 +0100 From: Lorenzo Pieralisi To: Remi Pommarel Cc: Thomas Petazzoni , Bjorn Helgaas , Ellie Reeves , linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] PCI: aardvark: Use LTSSM state to build link training flag Message-ID: <20190430113427.GA18742@e121166-lin.cambridge.arm.com> References: <20190316161243.29517-1-repk@triplefau.lt> <20190425110830.GC10833@e121166-lin.cambridge.arm.com> <20190425142353.GO2754@voidbox.localdomain> <20190425150640.GA20770@e121166-lin.cambridge.arm.com> <20190429153234.GS2754@voidbox.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190429153234.GS2754@voidbox.localdomain> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 29, 2019 at 05:32:35PM +0200, Remi Pommarel wrote: > Hi Lorenzo, > > Sorry for duplicates I forgot to include everyone. > > On Thu, Apr 25, 2019 at 04:06:40PM +0100, Lorenzo Pieralisi wrote: > > On Thu, Apr 25, 2019 at 04:23:53PM +0200, Remi Pommarel wrote: > > > Hi Lorenzo, > > > > > > On Thu, Apr 25, 2019 at 12:08:30PM +0100, Lorenzo Pieralisi wrote: > > > > On Sat, Mar 16, 2019 at 05:12:43PM +0100, Remi Pommarel wrote: > > > > > The PCI_EXP_LNKSTA_LT flag in the emulated root device's PCI_EXP_LNKSTA > > > > > config register does not reflect the actual link training state and is > > > > > always cleared. The Link Training and Status State Machine (LTSSM) flag > > > > > in 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 setting the PCI_EXP_LINCTL_RL flag does not > > > > > instantly imply a LTSSM state change (e.g. L0s to recovery state > > > > > transition takes some time), LTSSM can be in L0 but link training has > > > > > not finished yet. Thus a lower L0 LTSSM state followed by a L0 or upper > > > > > state sequence has to be seen to be sure that link training has been > > > > > done. > > > > > > > > Hi Remi, > > > > > > > > I am a bit confused, so you are saying that the LTSSM flag in the > > > > LMI config register can't be used to detect when training is completed ? > > > > > > Not exactly, I am saying that PCI_EXP_LNKSTA_LT from PCI_EXP_LNKSTA > > > register can't be used with this hardware, but can be emulated with > > > LTSSM flag. > > > > > > > > > > > Certainly it can't be used by ASPM core that relies on: > > > > > > > > PCI_EXP_LNKSTA_LT flag > > > > > > > > in the PCI_EXP_LNKSTA register, and that's what you are setting through > > > > this timeout mechanism IIUC. > > > > > > > > Please elaborate on that. > > > > > > The problem here is that the hardware does not change PCI_EXP_LNKSTA_LT > > > at all. So in order to support link re-training feature we need to > > > emulate this flag. To do so LTSSM flag can be used. > > > > Understood. > > > > > Indeed we can set the emulated PCI_EXP_LNKSTA_LT as soon as re-training > > > is asked and wait for LTSSM flag to be back to a configured state > > > (e.g. L0, L0s) before clearing it. > > > > The check for the LTSSM is carried out through advk_pcie_link_up() > > (ie register CFG_REG), correct ? > > > > Yes that is correct. > > > > The problem with that is that LTSSM flag does not change instantly after > > > link re-training has been asked, and will stay in configured state for a > > > small amount of time. So the idea is to poll the LTSSM flag and wait for > > > it to enter a recovery state then waiting for it to be back in > > > configured state. > > > > When you say "poll" you mean checking advk_pcie_link_up() ? > > > > I mean checking advk_pcie_link_up() in a loop. This loop is done by the > user (e.g. ASPM core). ASPM core waits for PCI_EXP_LNKSTA_LT to be > cleared in pcie_aspm_configure_common_clock() just after it has set > PCI_EXP_LNKCTL_RL. > > So the idea was to check advk_pcie_link_up() each time ASPM core checks > the PCI_EXP_LNKSTA_LT flag. Please see below patch for an alternative > to that. > > > More below on the code. > > > > > The timeout is only here as a fallback in the unlikely event that we > > > missed the LTSSM flag entering recovery state. > > > > > > > > > > > I am picking Bjorn's brain on this patch since what you are doing > > > > seems quite arbitrary and honestly it is a bit of a hack. > > > > > > Yes, sorry, it is a bit of a hack because I try to workaround a > > > hardware issue. > > > > No problems, it is not your fault. > > > > > > Please note that vendor has been contacted about this in the meantime > > > and answered the following: > > > > > > "FW can poll LTSSM state equals any of the following values: 0xB or 0xD > > > or 0xC or 0xE. After that, polls for LTSSM equals 0x10. For your > > > information, LTSSM will transit from 0x10 -> 0xB -> 0xD -> 0xC or 0xE > > > ........... -> 0x10". > > > > > > It is basically what this patch does, I've just added a timeout fallback > > > to not poll LTSSM state forever if its transition to 0xB, 0xD, 0xC or > > > 0xE has been missed. > > > > When you say "missed" you mean advk_pcie_link_up() returning true, right ? > > > > Not exactly, I mean that LTSSM had the time to go down and back up > between advk_pcie_link_up() because, for example, ASPM core loop took > too much time between two PCI_EXP_LNKSTA_LT flag checks. > > > [...] > > > > > > > +static int advk_pcie_link_retraining(struct advk_pcie *pcie) > > > > > +{ > > > > > + if (!advk_pcie_link_up(pcie)) { > > > > That's the bit I find confusing. Is this check here to detect if the > > link went through the sequence below ? Should not it be carried > > out only if (pcie->rl_asked == 1) ? > > > > "... LTSSM will transit from 0x10 -> 0xB -> 0xD -> 0xC or 0xE > > ........... -> 0x10". > > Yes it is the check to detect the sequence. advk_pcie_link_up() returns > false if LTSSM <= 0x10. > > This cannot be done only if (pcie->rl_asked == 1) because I still > want this function to return 1 if link is still down. > > > > > > > > + pcie->rl_asked = 0; > > > > Why ? > > > > rl_asked is not a good name, I could have called it > pcie->wait_for_link_down instead. So if advk_pcie_link_up() returns > false that means that we don't need to wait for link being down any more > and just wait for (LTSSM >= 0x10). In this case the delay is not needed. > > > > > > + return 1; > > > > > + } > > > > > + > > > > > + if (pcie->rl_asked && time_before(jiffies, pcie->rl_deadline)) > > > > > + return 1; > > > > This ensures that if the LTSSM >= 0x10 we still wait for a delay before > > considering the link up (because I suppose, after asking a retraining > > it takes a while for the LTSSM state to become < 0x10), correct ? > > Yes it takes a while to become < 0x10 after retraining hence the delay. > But here we don't need to always wait for a delay. Indeed if we've > already seen the link being < 0x10 (i.e if "pcie->rl_asked == 0") and > if after that link is >= 0x10 then we know that retraining process has > finished. > > Anyway I did it this way because I wanted to keep > advk_pci_bridge_emul_pcie_conf_write() from polling. But this is > obviously a bad reason as it makes the code way too complex and relies > on user (ASPM core) to do the poll instead. > > So if you find the following better I'll send a v3 with that: > > --- > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c > index eb58dfdaba1b..67e8ae4e313e 100644 > --- a/drivers/pci/controller/pci-aardvark.c > +++ b/drivers/pci/controller/pci-aardvark.c > @@ -180,6 +180,9 @@ > #define LINK_WAIT_MAX_RETRIES 10 > #define LINK_WAIT_USLEEP_MIN 90000 > #define LINK_WAIT_USLEEP_MAX 100000 > +#define RETRAIN_WAIT_MAX_RETRIES 20 > +#define RETRAIN_WAIT_USLEEP_MIN 2000 > +#define RETRAIN_WAIT_USLEEP_MAX 5000 > > #define MSI_IRQ_NUM 32 > > @@ -239,6 +242,17 @@ 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; > + usleep_range(RETRAIN_WAIT_USLEEP_MIN, RETRAIN_WAIT_USLEEP_MAX); > + } > +} > + > static void advk_pcie_setup_hw(struct advk_pcie *pcie) > { > u32 reg; > @@ -426,11 +440,19 @@ advk_pci_bridge_emul_pcie_conf_read(struct pci_bridge_emul *bridge, > return PCI_BRIDGE_EMUL_HANDLED; > } > > + case PCI_EXP_LNKCTL: { > + u32 val = advk_readl(pcie, PCIE_CORE_PCIEXP_CAP + reg) & > + ~(PCI_EXP_LNKSTA_LT << 16); > + if (!advk_pcie_link_up(pcie)) Is this correct ? "PCI Express Base Specification Rev4.0 Version 1.0" page 758 "Link Training: this read-only bit indicates that the physical layer LTSSM is in the Configuration or Recovery state or that 1b was written to the Retrain Link..." Isn't that a subset of states for which !advk_pcie_link_up() return true ? Lorenzo > + 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; > + > case PCI_EXP_LNKCTL: > advk_writel(pcie, new, PCIE_CORE_PCIEXP_CAP + reg); > + if (new & PCI_EXP_LNKCTL_RL) > + advk_pcie_wait_for_retrain(pcie); > break; > > case PCI_EXP_RTCTL: