linux-kernel - [PATCH v1 0/1] phy: freescale: imx8m-pcie: facing pcie link-up instability

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Date: Fri, 22 Mar 2024 14:06:31 +0100
From: Marcel Ziswiler <marcel@...wiler.com>
To: linux-phy@...ts.infradead.org
Cc: linux-imx@....com,
	Lucas Stach <l.stach@...gutronix.de>,
	linux-arm-kernel@...ts.infradead.org,
	kernel@...gutronix.de,
	Richard Zhu <hongxing.zhu@....com>,
	linux-kernel@...r.kernel.org,
	Marcel Ziswiler <marcel.ziswiler@...adex.com>,
	Fabio Estevam <festevam@...il.com>,
	Heiko Stuebner <heiko@...ech.de>,
	Kishon Vijay Abraham I <kishon@...nel.org>,
	Marc Kleine-Budde <mkl@...gutronix.de>,
	Rob Herring <robh@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Shawn Guo <shawnguo@...nel.org>,
	Tim Harvey <tharvey@...eworks.com>,
	Vinod Koul <vkoul@...nel.org>,
	Yang Li <yang.lee@...ux.alibaba.com>,
	imx@...ts.linux.dev
Subject: [PATCH v1 0/1] phy: freescale: imx8m-pcie: facing pcie link-up instability

From: Marcel Ziswiler <marcel.ziswiler@...adex.com>

In our automated testing setup, we use Delock Mini-PCIe SATA cards [1].
While this setup has proven very stable overall we noticed upstream on
the i.MX8M Mini fails quite regularly (about 50/50) to bring up the PCIe
link while with NXP's downstream BSP 5.15.71_2.2.2 it always works. As
that old downstream stuff was quite different, I first also tried NXP's
latest downstream BSP 6.1.55_2.2.0 which from a PCIe point of view is
fairly vanilla, however, also there the PCIe link-up was not stable.
Comparing and debugging I noticed that upstream explicitly configures
the AUX_PLL_REFCLK_SEL to I_PLL_REFCLK_FROM_SYSPLL while working
downstream [2] leaving it at reset defaults of AUX_IN (PLL clock).
Unfortunately, the TRM does not mention any further details about this
register (both for the i.MX 8M Mini as well as the Plus). Maybe somebody
from NXP could further comment on this?

BTW: On the i.MX 8M Plus we have not seen any issues with PCIe with the
exact same setup which is why I left it unchanged.

[1] https://www.delock.com/produkt/95233/merkmale.html
[2] https://github.com/nxp-imx/linux-imx/blob/lf-5.15.71-2.2.0/drivers/pci/controller/dwc/pci-imx6.c#L1548

Marcel Ziswiler (1):
  phy: freescale: imx8m-pcie: fix pcie link-up instability

 drivers/phy/freescale/phy-fsl-imx8m-pcie.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--
2.44.0