linux-kernel - [PATCH v2] PCI: DWC: meson: add 256 bytes MRRS quirk

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Date:   Tue, 27 Jul 2021 10:30:00 +0800
From:   Artem Lapkin <email2tema@...il.com>
To:     narmstrong@...libre.com
Cc:     yue.wang@...ogic.com, khilman@...libre.com,
        lorenzo.pieralisi@....com, robh@...nel.org, kw@...ux.com,
        jbrunet@...libre.com, christianshewitt@...il.com,
        martin.blumenstingl@...glemail.com, linux-pci@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org,
        art@...das.com, nick@...das.com, gouwa@...das.com
Subject: [PATCH v2] PCI: DWC: meson: add 256 bytes MRRS quirk

256 bytes maximum read request size. They can't handle
anything larger than this. So force this limit on
any devices attached under these ports.

Come-from: https://lkml.org/lkml/2021/6/18/160
Come-from: https://lkml.org/lkml/2021/6/19/19

It only affects PCIe in P2P, in non-P2P is will certainly affect
transfers on the internal SoC/Processor/Chip internal bus/fabric.

These quirks are currently implemented in the
controller driver and only applies when the controller has been probed
and to each endpoint detected on this particular controller.

Continue having separate quirks for each controller if the core
isn't the right place to handle MPS/MRRS.

>> Neil

Signed-off-by: Artem Lapkin <art@...das.com>
---
 drivers/pci/controller/dwc/pci-meson.c | 31 ++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/drivers/pci/controller/dwc/pci-meson.c b/drivers/pci/controller/dwc/pci-meson.c
index 686ded034..1498950de 100644
--- a/drivers/pci/controller/dwc/pci-meson.c
+++ b/drivers/pci/controller/dwc/pci-meson.c
@@ -466,6 +466,37 @@ static int meson_pcie_probe(struct platform_device *pdev)
 	return ret;
 }
 
+static void meson_mrrs_limit_quirk(struct pci_dev *dev)
+{
+	struct pci_bus *bus = dev->bus;
+	int mrrs, mrrs_limit = 256;
+	static const struct pci_device_id bridge_devids[] = {
+		{ PCI_DEVICE(PCI_VENDOR_ID_SYNOPSYS, PCI_DEVICE_ID_SYNOPSYS_HAPSUSB3) },
+		{ 0, },
+	};
+
+	/* look for the matching bridge */
+	while (!pci_is_root_bus(bus)) {
+		/*
+		 * 256 bytes maximum read request size. They can't handle
+		 * anything larger than this. So force this limit on
+		 * any devices attached under these ports.
+		 */
+		if (!pci_match_id(bridge_devids, bus->self)) {
+			bus = bus->parent;
+			continue;
+		}
+
+		mrrs = pcie_get_readrq(dev);
+		if (mrrs > mrrs_limit) {
+			pci_info(dev, "limiting MRRS %d to %d\n", mrrs, mrrs_limit);
+			pcie_set_readrq(dev, mrrs_limit);
+		}
+		break;
+	}
+}
+DECLARE_PCI_FIXUP_ENABLE(PCI_ANY_ID, PCI_ANY_ID, meson_mrrs_limit_quirk);
+
 static const struct of_device_id meson_pcie_of_match[] = {
 	{
 		.compatible = "amlogic,axg-pcie",
-- 
2.25.1