Re: [PATCH V4] Revert "PCI: tegra194: Enable support for 256 Byte payload"

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Hi Krzysztof, Bjorn,

On 18/07/2023 03:52, Vidya Sagar wrote:
After commit 4fb8e46c1bc4 ("PCI: tegra194: Enable support for 256 Byte
payload"), we set MPS=256 for tegra194 Root Ports.

By default (CONFIG_PCIE_BUS_DEFAULT set and no "pci=pcie_bus_*"
parameter), Linux configures the MPS of every device to match the
upstream bridge, which is impossible if the Root Port has MPS=256
and a device only supports MPS=128.

This scenario results in uncorrectable Malformed TLP errors if the
Root Port sends TLPs with payloads larger than 128 bytes.  These
errors can be avoided by using the "pci=pcie_bus_safe" parameter,
but it doesn't seem to be a good idea to always have this parameter
even for basic functionality to work.

Revert commit 4fb8e46c1bc4 ("PCI: tegra194: Enable support for 256 Byte
payload") so the Root Ports default to MPS=128, which all devices
support.

If peer-to-peer DMA is not required, one can use "pci=pcie_bus_perf"
to get the benefit of larger MPS settings.

[ rewrote commit message based on Bjorn's suggestion ]

Fixes: 4fb8e46c1bc4 ("PCI: tegra194: Enable support for 256 Byte payload")
Signed-off-by: Vidya Sagar <vidyas@xxxxxxxxxx>
---
V4:
* Rewrote commit message based on Bjorn's suggestion

V3:
* Fixed a build issue

V2:
* Addressed review comments from Bjorn

  drivers/pci/controller/dwc/pcie-tegra194.c | 14 ++------------
  1 file changed, 2 insertions(+), 12 deletions(-)

diff --git a/drivers/pci/controller/dwc/pcie-tegra194.c b/drivers/pci/controller/dwc/pcie-tegra194.c
index 4fdadc7b045f..a772faff14b5 100644
--- a/drivers/pci/controller/dwc/pcie-tegra194.c
+++ b/drivers/pci/controller/dwc/pcie-tegra194.c
@@ -900,11 +900,6 @@ static int tegra_pcie_dw_host_init(struct dw_pcie_rp *pp)
  		pcie->pcie_cap_base = dw_pcie_find_capability(&pcie->pci,
  							      PCI_CAP_ID_EXP);
- val_16 = dw_pcie_readw_dbi(pci, pcie->pcie_cap_base + PCI_EXP_DEVCTL);
-	val_16 &= ~PCI_EXP_DEVCTL_PAYLOAD;
-	val_16 |= PCI_EXP_DEVCTL_PAYLOAD_256B;
-	dw_pcie_writew_dbi(pci, pcie->pcie_cap_base + PCI_EXP_DEVCTL, val_16);
-
  	val = dw_pcie_readl_dbi(pci, PCI_IO_BASE);
  	val &= ~(IO_BASE_IO_DECODE | IO_BASE_IO_DECODE_BIT8);
  	dw_pcie_writel_dbi(pci, PCI_IO_BASE, val);
@@ -1756,7 +1751,6 @@ static void pex_ep_event_pex_rst_deassert(struct tegra_pcie_dw *pcie)
  	struct device *dev = pcie->dev;
  	u32 val;
  	int ret;
-	u16 val_16;
if (pcie->ep_state == EP_STATE_ENABLED)
  		return;
@@ -1887,20 +1881,16 @@ static void pex_ep_event_pex_rst_deassert(struct tegra_pcie_dw *pcie)
  	pcie->pcie_cap_base = dw_pcie_find_capability(&pcie->pci,
  						      PCI_CAP_ID_EXP);
- val_16 = dw_pcie_readw_dbi(pci, pcie->pcie_cap_base + PCI_EXP_DEVCTL);
-	val_16 &= ~PCI_EXP_DEVCTL_PAYLOAD;
-	val_16 |= PCI_EXP_DEVCTL_PAYLOAD_256B;
-	dw_pcie_writew_dbi(pci, pcie->pcie_cap_base + PCI_EXP_DEVCTL, val_16);
-
  	/* Clear Slot Clock Configuration bit if SRNS configuration */
  	if (pcie->enable_srns) {
+		u16 val_16;
+
  		val_16 = dw_pcie_readw_dbi(pci, pcie->pcie_cap_base +
  					   PCI_EXP_LNKSTA);
  		val_16 &= ~PCI_EXP_LNKSTA_SLC;
  		dw_pcie_writew_dbi(pci, pcie->pcie_cap_base + PCI_EXP_LNKSTA,
  				   val_16);
  	}
-
  	clk_set_rate(pcie->core_clk, GEN4_CORE_CLK_FREQ);
val = (ep->msi_mem_phys & MSIX_ADDR_MATCH_LOW_OFF_MASK);



I see a version of this patch here ...

https://git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git/log/?h=controller/tegra194

However, I don't see this in -next yet. If you are happy with this latest version, could we get this into -next?

FWIW ...

Acked-by: Jon Hunter <jonathanh@xxxxxxxxxx>

Thanks!
Jon

--
nvpublic



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