Re: [PATCH V3 2/2] PCI: dwc: Add support to configure for ECRC
From: Vidya Sagar
Date: Mon Nov 02 2020 - 22:27:15 EST
On 11/3/2020 4:32 AM, Bjorn Helgaas wrote:
External email: Use caution opening links or attachments
On Thu, Oct 29, 2020 at 11:09:59AM +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. This patch does the required programming in ATU upon
querying the system policy for ECRC.
I guess this is a hardware defect, right?
Yes. This is common across all DWC implementations (version 4.90 precisely)
How much of a problem would it be if we instead added a "no_ecrc"
quirk for this hardware so we never enabled ECRC?
Well, on Tegra for some of the high fidelity use cases, ECRC is required
to be turned on and if it can be done safely with these patches, why
shouldn't we not enable ECRC at all?
IIUC, the current Linux support of ECRC is a single choice at
boot-time: by default ECRC is not enabled, but if you boot with
"pci=ecrc=on", we turn on ECRC for every device.
That seems like the minimal support, but I think the spec allows ECRC
to be enabled selectively, on individual devices. I can imagine a
sysfs knob that would allow us to enable/disable ECRC per-device at
run-time.
If we had such a sysfs knob, it would be pretty ugly and maybe
impractical to work around this hardware issue. So I'm a little bit
hesitant to add functionality that might have to be removed in the
future.
Agree with this. But since it is a boot-time choice at this point, I
think we can still go ahead with this approach to have a working ECRC
mechanism right? I don't see any sysfs knob for AER controlling at this
point.
Signed-off-by: Vidya Sagar <vidyas@xxxxxxxxxx>
Reviewed-by: Jingoo Han <jingoohan1@xxxxxxxxx>
---
V3:
* Added 'Reviewed-by: Jingoo Han <jingoohan1@xxxxxxxxx>'
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)
+ val = val | pcie_is_ecrc_enabled() << PCIE_ATU_TD_SHIFT;
+ 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 e7f441441db2..b01ef407fd52 100644
--- a/drivers/pci/controller/dwc/pcie-designware.h
+++ b/drivers/pci/controller/dwc/pcie-designware.h
@@ -89,6 +89,7 @@
#define PCIE_ATU_TYPE_IO 0x2
#define PCIE_ATU_TYPE_CFG0 0x4
#define PCIE_ATU_TYPE_CFG1 0x5
+#define PCIE_ATU_TD_SHIFT 8
#define PCIE_ATU_FUNC_NUM(pf) ((pf) << 20)
#define PCIE_ATU_CR2 0x908
#define PCIE_ATU_ENABLE BIT(31)
--
2.17.1