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Fri, 23 Oct 2026 17:39:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792777191; bh=waB3ovVdlrOaRg5kwbOJtqiQowW1jAyrixqhCwCH4EM=; h=From:Date:Subject:To:Cc:Reply-To; b=AXejTeFPl2g76hjcjwYj23tvvyPiO2O9fBFqIp0gibOAKU3RTySfEdImOH2NSaLTB v8WFO75gZAkCnXocqPuOOGzye3Tq7ejCrodL8fRfD039dKiMobU4snQwLW2FoHV6Uy g7g6glNTejVPw8vTK+WvuAKeIthwOqINFFXA4gHUt3cCGo3dH4wmqQbgOdb+MmrwiS U/ptzDjsmG8ZWm61OkPsXm+yqzFFquvLT4u8yABzqlU1RxspiInevzYju4mVsPjHg8 eWbYj2WG3AkCnD6XSKwROyREjI+mmWpqCisrIXL4HsXdTCbd78pJyjwZ/BYscPFcsc r4644y498UWWQ== Received: from nexus.subspace.kernel.org (localhost [IPv6:::1]) by lkml.kernel.org (Postfix) with ESMTP id E6F0944568; Fri, 23 Oct 2026 17:39:48 +0000 (UTC) From: Anthony Ruhier via B4 Relay Date: Fri, 23 Oct 2026 19:39:35 +0200 Subject: [PATCH] PCI: Disable LTR on Qualcomm WCN7850 [17cb:1107] to allow ASPM L1.2 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Message-Id: <20261023-quick-wcn7850-v1-1-9a139b9b2c8e@mailbox.org> X-B4-Tracking: v=1; b=H4sIAAAAAAAC/6tWKk4tykwtVrJSqFYqSi3LLM7MzwNyDHUUlJIzE vPSU3UzU4B8JSMDIzNDAyNj3cLSzORs3fLkPHMLUwPdRHNLI0szi+RkI9M0JaCegqLUtMwKsHn RsRB+cWlSVmpyCcgQpdpaAMlxQMFxAAAA X-Change-ID: 20261023-quick-wcn7850-a792968cc25f To: Bjorn Helgaas Cc: linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, Anthony Ruhier X-Mailer: b4 0.16.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=2159; i=aruhier@mailbox.org; s=2026; h=from:subject:message-id; bh=qVemxmolshXeAK74vDQvvG7KPXw1hF5ybwiK/r2mOek=; b=owGbwMvMwCV2okp4cvOBsLOMp9WSGLJuz37Cz7ZBaGX46ad/bsqxTZD6LcNw0ZBnqkJrwdacm 1pPv7ct6JjIwiDGxWAppshywbLg8eNb0ZO762y6YOawMoEMkRZpYAACFga+3MS8UiMdIz1TbUM9 QyBDx4iBi1MApnpDKMP/xMmyzmsuPG+6cth1W+oN4UOPFToOlfhzH0tV85ppVFDLzshw57/Enfl ZHiY5m8+oif48uOj39EBP86wX+2UXXYyvvi3JAQA= X-Developer-Key: i=aruhier@mailbox.org; a=openpgp; fpr=F4A378DD8D494AE48EBA554CB00FBC7D08D231D9 X-Endpoint-Received: by B4 Relay for aruhier@mailbox.org/2026 with auth_id=1292 X-Original-From: Anthony Ruhier Reply-To: aruhier@mailbox.org Content-Transfer-Encoding: 7bit From: Anthony Ruhier The WCN7850 Wifi/BT card, found in several Snapdragon X laptops, never enters ASPM L1.2 when LTR is enabled. Its firmware reads the LTR_L1.2_THRESHOLD set at enumeration and reports an LTR value just below it, so the L1.2 entry condition is never met and the link stays in L1.1. Windows does not set LTR Mechanism Enable for this device (verified by dumping the ACPI tables), and the link idles in L1.2 normally. Replicate the same behavior: clear PCI_EXP_DEVCTL2_LTR_EN for WCN7850 at enumeration and again on resume, as the LTR state is restored there. On a Lenovo Yoga Slim 7x (X1E80100) this allows the link to reach L1.2 and reduces idle power by about 70 mW. Signed-off-by: Anthony Ruhier --- drivers/pci/quirks.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c index 1aa87a3ef9ed..374c505981a0 100644 --- a/drivers/pci/quirks.c +++ b/drivers/pci/quirks.c @@ -3795,6 +3795,20 @@ DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_QCOM, 0x1103, quirk_no_bus_reset); /* WCN DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_QCOM, 0x1107, quirk_no_bus_reset); /* WCN7850 */ DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_QCOM, 0x0308, quirk_no_bus_reset); /* SDX62/SDX65 */ +/* + * The WCN7850 firmware reports an LTR just below the LTR_L1.2_THRESHOLD it + * sees at boot, preventing it to ever enter L1.2. + * With LTR disabled the link idles in L1.2, similar to what Windows does. + */ +static void quirk_wcn7850_disable_ltr(struct pci_dev *pdev) +{ + pcie_capability_clear_word(pdev, PCI_EXP_DEVCTL2, + PCI_EXP_DEVCTL2_LTR_EN); +} +DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_QCOM, 0x1107, quirk_wcn7850_disable_ltr); +DECLARE_PCI_FIXUP_RESUME_EARLY(PCI_VENDOR_ID_QCOM, 0x1107, + quirk_wcn7850_disable_ltr); + /* * Root port on some Cavium CN8xxx chips do not successfully complete a bus * reset when used with certain child devices. After the reset, config --- base-commit: 7be4bc52fd9e0e55dc9a2e0232b89427d2c4b614 change-id: 20261023-quick-wcn7850-a792968cc25f Best regards, -- Anthony Ruhier