linux-kernel - [PATCH v2 0/2] PCI: imx6: Add a method to handle CLKREQ# override

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Message-Id: <20250917093751.1520050-1-hongxing.zhu@nxp.com>
Date: Wed, 17 Sep 2025 17:37:49 +0800
From: Richard Zhu <hongxing.zhu@....com>
To: frank.li@....com,
	jingoohan1@...il.com,
	l.stach@...gutronix.de,
	lpieralisi@...nel.org,
	kwilczynski@...nel.org,
	mani@...nel.org,
	robh@...nel.org,
	bhelgaas@...gle.com,
	shawnguo@...nel.org,
	s.hauer@...gutronix.de,
	kernel@...gutronix.de,
	festevam@...il.com
Cc: linux-pci@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	imx@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 0/2] PCI: imx6: Add a method to handle CLKREQ# override

The CLKREQ# is an open drain, active low signal that is driven low by
the card to request reference clock.

But the CLKREQ# maybe reserved on some old device, compliant with CEM
r3.0 or before. Thus, this signal wouldn't be driven low by these old
devices.

Since the reference clock controlled by CLKREQ# may be required by i.MX
PCIe host too. To make sure this clock is ready even when the CLKREQ#
isn't driven low by the card(e.x old cards described above), force
CLKREQ# override active low for i.MX PCIe host during initialization.

The CLKREQ# override can be cleared safely when supports-clkreq is
present and PCIe link is up later. Because the CLKREQ# would be driven
low by the card in this case.

Main changes in v2:
- Update the commit message, and collect the reviewed-by tag.

[PATCH v2 1/2] PCI: dwc: Invoke post_init in dw_pcie_resume_noirq()
[PATCH v2 2/2] PCI: imx6: Add a method to handle CLKREQ# override

drivers/pci/controller/dwc/pci-imx6.c             | 35 +++++++++++++++++++++++++++++++++++
drivers/pci/controller/dwc/pcie-designware-host.c |  3 +++
2 files changed, 38 insertions(+)