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Date: Tue, 10 Nov 2020 14:50:20 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Vidya Sagar <vidyas@...dia.com>
Cc: jingoohan1@...il.com, gustavo.pimentel@...opsys.com,
lorenzo.pieralisi@....com, bhelgaas@...gle.com,
amurray@...goodpenguin.co.uk, robh@...nel.org, treding@...dia.com,
jonathanh@...dia.com, linux-pci@...r.kernel.org,
linux-kernel@...r.kernel.org, kthota@...dia.com,
mmaddireddy@...dia.com, sagar.tv@...il.com
Subject: Re: [PATCH] PCI: dwc: Add support to configure for ECRC
On Tue, Nov 10, 2020 at 12:56:11AM +0530, Vidya Sagar 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.
>
> Signed-off-by: Vidya Sagar <vidyas@...dia.com>
Modulo typos/formatting comments below,
Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>
Thanks for working through this.
> ---
> drivers/pci/controller/dwc/pcie-designware.c | 50 ++++++++++++++++++--
> drivers/pci/controller/dwc/pcie-designware.h | 1 +
> 2 files changed, 47 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> index c2dea8fc97c8..ebdc37a58e94 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.c
> +++ b/drivers/pci/controller/dwc/pcie-designware.c
> @@ -225,6 +225,44 @@ static void dw_pcie_writel_ob_unroll(struct dw_pcie *pci, u32 index, u32 reg,
> dw_pcie_writel_atu(pci, offset + reg, val);
> }
>
> +static inline u32 dw_pcie_enable_ecrc(u32 val)
> +{
> + /*
> + * DesignWare core version 4.90A has this strange design issue
> + * where the 'TD' bit in the Control register-1 of the ATU outbound
> + * region acts like an override for the ECRC setting i.e. the presence
> + * of TLP Digest(ECRC) in the outgoing TLPs is solely determined by
> + * this bit. This is contrary to the PCIe spec which says that the
> + * enablement of the ECRC is solely determined by the AER registers.
> + * Because of this, even when the ECRC is enabled through AER
> + * registers, the transactions going through ATU won't have TLP Digest
> + * as there is no way the AER sub-system could program the TD bit which
> + * is specific to DsignWare core.
s/DsignWare/DesignWare/
> + * The best way to handle this scenario is to program the TD bit
> + * always. It affects only the traffic from root port to downstream
> + * devices.
Convention is to separate paragraphs with blank lines, not to indent
the first line.
> + * At this point,
> + * When ECRC is enabled in AER registers, everything works
> + * normally
> + * When ECRC is NOT enabled in AER registers, then,
> + * on Root Port:- TLP Digest (DWord size) gets appended to each packet
> + * even through it is not required. Since downstream
> + * TLPs are mostly for configuration accesses and BAR
> + * accesses, they are not in critical path and won't
> + * have much negative effect on the performance.
> + * on End Point:- TLP Digest is received for some/all the packets coming
> + * from the root port. TLP Digest is ignored because,
> + * as per the PCIe Spec r5.0 v1.0 section 2.2.3 "TLP Digest Rules",
Wrap to fit in 80 columns.
> + * when an endpoint receives TLP Digest when its
> + * ECRC check functionality is disabled in AER registers,
> + * received TLP Digest is just ignored.
> + * Since there is no issue or error reported either side, best way to
> + * handle the scenario is to program TD bit by default.
> + */
> +
> + return val | PCIE_ATU_TD;
> +}
> +
> static void dw_pcie_prog_outbound_atu_unroll(struct dw_pcie *pci, u8 func_no,
> int index, int type,
> u64 cpu_addr, u64 pci_addr,
> @@ -245,8 +283,10 @@ static void dw_pcie_prog_outbound_atu_unroll(struct dw_pcie *pci, u8 func_no,
> lower_32_bits(pci_addr));
> dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_UPPER_TARGET,
> upper_32_bits(pci_addr));
> - dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_REGION_CTRL1,
> - type | PCIE_ATU_FUNC_NUM(func_no));
> + val = type | PCIE_ATU_FUNC_NUM(func_no);
> + if (pci->version == 0x490A)
> + val = dw_pcie_enable_ecrc(val);
> + dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_REGION_CTRL1, val);
> dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_REGION_CTRL2,
> PCIE_ATU_ENABLE);
>
> @@ -292,8 +332,10 @@ 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)
> + val = dw_pcie_enable_ecrc(val);
> + dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, val);
> dw_pcie_writel_dbi(pci, PCIE_ATU_CR2, PCIE_ATU_ENABLE);
>
> /*
> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> index 9d2f511f13fa..285c0ae364ae 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.h
> +++ b/drivers/pci/controller/dwc/pcie-designware.h
> @@ -88,6 +88,7 @@
> #define PCIE_ATU_TYPE_IO 0x2
> #define PCIE_ATU_TYPE_CFG0 0x4
> #define PCIE_ATU_TYPE_CFG1 0x5
> +#define PCIE_ATU_TD BIT(8)
> #define PCIE_ATU_FUNC_NUM(pf) ((pf) << 20)
> #define PCIE_ATU_CR2 0x908
> #define PCIE_ATU_ENABLE BIT(31)
> --
> 2.17.1
>
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