From: Bjorn Helgaas <helgaas@kernel.org>
To: Richard Zhu <hongxing.zhu@nxp.com>
Cc: frank.li@nxp.com, jingoohan1@gmail.com, l.stach@pengutronix.de,
lpieralisi@kernel.org, kwilczynski@kernel.org, mani@kernel.org,
robh@kernel.org, bhelgaas@google.com, shawnguo@kernel.org,
s.hauer@pengutronix.de, kernel@pengutronix.de,
festevam@gmail.com, linux-pci@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, imx@lists.linux.dev,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 2/2] PCI: imx6: Add a method to handle CLKREQ# override active low
Date: Wed, 17 Sep 2025 17:23:56 -0500 [thread overview]
Message-ID: <20250917222356.GA1879221@bhelgaas> (raw)
In-Reply-To: <20250917093751.1520050-3-hongxing.zhu@nxp.com>
On Wed, Sep 17, 2025 at 05:37:51PM +0800, Richard Zhu wrote:
> 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.
Can you include a citation to a relevant section in the CEM spec?
Maybe the point is that CLKREQ# is an optional signal added in PCIe
CEM r4.0, sec 2?
If that's accurate, we can add it when applying, no need to repost for
that.
> 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.
next prev parent reply other threads:[~2025-09-17 22:24 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-09-17 9:37 [PATCH v2 0/2] PCI: imx6: Add a method to handle CLKREQ# override Richard Zhu
2025-09-17 9:37 ` [PATCH v2 1/2] PCI: dwc: Invoke post_init in dw_pcie_resume_noirq() Richard Zhu
2025-09-17 9:37 ` [PATCH v2 2/2] PCI: imx6: Add a method to handle CLKREQ# override active low Richard Zhu
2025-09-17 22:23 ` Bjorn Helgaas [this message]
2025-09-18 3:04 ` Hongxing Zhu
2025-09-20 7:34 ` [PATCH v2 0/2] PCI: imx6: Add a method to handle CLKREQ# override Manivannan Sadhasivam
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20250917222356.GA1879221@bhelgaas \
--to=helgaas@kernel.org \
--cc=bhelgaas@google.com \
--cc=festevam@gmail.com \
--cc=frank.li@nxp.com \
--cc=hongxing.zhu@nxp.com \
--cc=imx@lists.linux.dev \
--cc=jingoohan1@gmail.com \
--cc=kernel@pengutronix.de \
--cc=kwilczynski@kernel.org \
--cc=l.stach@pengutronix.de \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pci@vger.kernel.org \
--cc=lpieralisi@kernel.org \
--cc=mani@kernel.org \
--cc=robh@kernel.org \
--cc=s.hauer@pengutronix.de \
--cc=shawnguo@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox