From: "Pali Rohár" <pali@kernel.org>
To: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Bjorn Helgaas <helgaas@kernel.org>, Rob Herring <robh@kernel.org>,
linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH v2] PCI: aardvark: Update comment about disabling link training
Date: Wed, 2 Dec 2020 19:46:59 +0100 [thread overview]
Message-ID: <20201202184659.3795-1-pali@kernel.org> (raw)
In-Reply-To: <20200924084618.12442-1-pali@kernel.org>
It is not HW bug or workaround for some cards but it is requirement by PCI
Express spec. After fundamental reset is needed 100ms delay prior enabling
link training. So update comment in code to reflect this requirement.
Signed-off-by: Pali Rohár <pali@kernel.org>
---
Changes in v2:
* Add reference to the PCI Express spec
---
drivers/pci/controller/pci-aardvark.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
index 0be485a25327..f742da2a20ee 100644
--- a/drivers/pci/controller/pci-aardvark.c
+++ b/drivers/pci/controller/pci-aardvark.c
@@ -259,7 +259,14 @@ static void advk_pcie_issue_perst(struct advk_pcie *pcie)
if (!pcie->reset_gpio)
return;
- /* PERST does not work for some cards when link training is enabled */
+ /*
+ * As required by PCI Express spec (PCI Express Base Specification, REV.
+ * 4.0 PCI Express, February 19 2014, 6.6.1 Conventional Reset) a delay
+ * for at least 100ms after de-asserting PERST# signal is needed before
+ * link training is enabled. So ensure that link training is disabled
+ * prior de-asserting PERST# signal to fulfill that PCI Express spec
+ * requirement.
+ */
reg = advk_readl(pcie, PCIE_CORE_CTRL0_REG);
reg &= ~LINK_TRAINING_EN;
advk_writel(pcie, reg, PCIE_CORE_CTRL0_REG);
--
2.20.1
next prev parent reply other threads:[~2020-12-02 18:48 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-24 8:46 [PATCH] PCI: aardvark: Update comment about disabling link training Pali Rohár
2020-09-24 15:11 ` Bjorn Helgaas
2020-09-24 15:22 ` Pali Rohár
2020-10-11 17:21 ` Pali Rohár
2020-11-29 23:17 ` Pali Rohár
2020-11-30 10:52 ` Lorenzo Pieralisi
2020-12-02 18:41 ` Pali Rohár
2020-12-02 18:46 ` Pali Rohár [this message]
2020-12-07 16:42 ` [PATCH v2] " Lorenzo Pieralisi
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=20201202184659.3795-1-pali@kernel.org \
--to=pali@kernel.org \
--cc=helgaas@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pci@vger.kernel.org \
--cc=lorenzo.pieralisi@arm.com \
--cc=robh@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;
as well as URLs for NNTP newsgroup(s).