linux-kernel - RE: [PATCH V3 2/2] PCI: dwc: Add support to configure for ECRC

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Message-ID: <DM5PR12MB1835187E112C8854D4483E42DA100@DM5PR12MB1835.namprd12.prod.outlook.com>
Date:   Mon, 2 Nov 2020 22:38:50 +0000
From:   Gustavo Pimentel <Gustavo.Pimentel@...opsys.com>
To:     Rob Herring <robh@...nel.org>
CC:     Vidya Sagar <vidyas@...dia.com>, Jingoo Han <jingoohan1@...il.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Andrew Murray <amurray@...goodpenguin.co.uk>,
        Thierry Reding <treding@...dia.com>,
        Jon Hunter <jonathanh@...dia.com>,
        PCI <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kthota@...dia.com" <kthota@...dia.com>,
        Manikanta Maddireddy <mmaddireddy@...dia.com>,
        "sagar.tv@...il.com" <sagar.tv@...il.com>
Subject: RE: [PATCH V3 2/2] PCI: dwc: Add support to configure for ECRC

On Mon, Nov 2, 2020 at 21:16:52, Rob Herring <robh@...nel.org> wrote:

> On Mon, Nov 2, 2020 at 9:12 AM Gustavo Pimentel
> <Gustavo.Pimentel@...opsys.com> wrote:
> >
> > On Mon, Nov 2, 2020 at 14:27:9, Vidya Sagar <vidyas@...dia.com> wrote:
> >
> > >
> > >
> > > On 11/2/2020 7:45 PM, Rob Herring wrote:
> > > > External email: Use caution opening links or attachments
> > > >
> > > >
> > > > On Thu, Oct 29, 2020 at 12:40 AM Vidya Sagar <vidyas@...dia.com> wrote:
> > > >>
> > > >> DesignWare core has a TLP digest (TD) override bit in one of the control
> > > >> registers of ATU. This bit also needs to be programmed for proper ECRC
> > > >> functionality. This is currently identified as an issue with DesignWare
> > > >> IP version 4.90a. This patch does the required programming in ATU upon
> > > >> querying the system policy for ECRC.
> > > >>
> > > >> Signed-off-by: Vidya Sagar <vidyas@...dia.com>
> > > >> Reviewed-by: Jingoo Han <jingoohan1@...il.com>
> > > >> ---
> > > >> V3:
> > > >> * Added 'Reviewed-by: Jingoo Han <jingoohan1@...il.com>'
> > > >>
> > > >> V2:
> > > >> * Addressed Jingoo's review comment
> > > >> * Removed saving 'td' bit information in 'dw_pcie' structure
> > > >>
> > > >>   drivers/pci/controller/dwc/pcie-designware.c | 8 ++++++--
> > > >>   drivers/pci/controller/dwc/pcie-designware.h | 1 +
> > > >>   2 files changed, 7 insertions(+), 2 deletions(-)
> > > >>
> > > >> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> > > >> index b5e438b70cd5..cbd651b219d2 100644
> > > >> --- a/drivers/pci/controller/dwc/pcie-designware.c
> > > >> +++ b/drivers/pci/controller/dwc/pcie-designware.c
> > > >> @@ -246,6 +246,8 @@ static void dw_pcie_prog_outbound_atu_unroll(struct dw_pcie *pci, u8 func_no,
> > > >>          dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_UPPER_TARGET,
> > > >>                                   upper_32_bits(pci_addr));
> > > >>          val = type | PCIE_ATU_FUNC_NUM(func_no);
> > > >> +       if (pci->version == 0x490A)
> > > >> +               val = val | pcie_is_ecrc_enabled() << PCIE_ATU_TD_SHIFT;
> > > >>          val = upper_32_bits(size - 1) ?
> > > >>                  val | PCIE_ATU_INCREASE_REGION_SIZE : val;
> > > >>          dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_REGION_CTRL1, val);
> > > >> @@ -294,8 +296,10 @@ static void __dw_pcie_prog_outbound_atu(struct dw_pcie *pci, u8 func_no,
> > > >>                             lower_32_bits(pci_addr));
> > > >>          dw_pcie_writel_dbi(pci, PCIE_ATU_UPPER_TARGET,
> > > >>                             upper_32_bits(pci_addr));
> > > >> -       dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, type |
> > > >> -                          PCIE_ATU_FUNC_NUM(func_no));
> > > >> +       val = type | PCIE_ATU_FUNC_NUM(func_no);
> > > >> +       if (pci->version == 0x490A)
> > > >
> > > > Is this even possible? Are the non-unroll ATU registers available post 4.80?
> > > I'm not sure. Gustavo might have information about this. I made this
> > > change so that it is taken care off even if they available.
> >
> > The Synopsys DesignWare PCIe IP is highly configurable, therefore is
> > dependable on what the design team has configured for their solution.
> > Although Synopsys doesn't recommend the use of non-unroll ATU, the
> > customers are free to select what they want for their design.
> 
> Okay, then there's a bug in the driver if the version is set to 0x480A
> or later and non-unroll is used:
> 
> if (pci->version >= 0x480A || (!pci->version &&
>        dw_pcie_iatu_unroll_enabled(pci))) {
> 
> Probably can just drop the version checking. The detection should always work.

Hi Rob,

The "detection" is based on the assumption that the read value on 
PCIE_ATU_VIEWPORT register is 0xffffffff (which is a hard-coded value by 
design), if it's true then the iATU is unrolled and the function returns 
1, otherwise is non-unrolled returns 0. So like you said it should always 
work, however, this code behavior was changed by Kishon on the following 
patch 2aadcb0cd39 ("PCI: dwc: Fix ATU identification for designware 
version >= 4.80"). His patch makes me believe that on keystone platform 
the read operation on that register causes some unpredicted behavior 
leads his platform to crash/abort, that's why he created this alternative 
version approach to avoid the "detection" algorithm.

From what I'm seeing the only drivers that use this "version" approach 
are the keystone and intel-gw (which probably doesn't need it).

To summarize, this is a workaround so that the keystone driver doesn't 
break independent of the controller IP version.

-Gustavo
> 
> Rob