Re: [PATCH] PCI: amlogic: meson: Don't use FAST_LINK_MODE to set up link

Hi Yue,

On Thu, 07 May 2020 02:43:31 +0100,
"yue.wang@amlogic.com" [off-list ref] wrote:

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Marc,

This patch looks all right. I tested in my meson board and pcie
EP(QCA9888) worked well.

Fast link mode is enabled for simulation purposes, it should be
disabled in the real hardware.

Thanks for confirming my reading of the manual and having tested it.
Can I take this as an "Acked-by:" and a "Tested-by:"?

Cheers,

	M.

yue.wang@amlogic.com
 
From: Marc Zyngier
Date: 2020-05-06 18:43
To: linux-pci; linux-amlogic; linux-arm-kernel; linux-kernel; Kevin Hilman; Yue Wang
CC: Bjorn Helgaas; Rob Herring; Lorenzo Pieralisi
Subject: Re: [PATCH] PCI: amlogic: meson: Don't use FAST_LINK_MODE to set up link
On Wed, 29 Apr 2020 17:42:30 +0100
Marc Zyngier [off-list ref] wrote:
 

quoted

My vim3l board stubbornly refuses to play ball with a bog
standard PCIe switch (ASM1184e), spitting all kind of errors
ranging from link never coming up to crazy things like downstream
ports falling off the face of the planet.

Upon investigating how the PCIe RC is configured, I found the
following nugget: the Sysnopsys DWC PCIe Reference Manual, in the
section dedicated to the PLCR register, describes bit 7 (FAST_LINK_MODE)
as:

"Sets all internal timers to fast mode for simulation purposes."

I completely understand the need for setting this bit from a simulation
perspective, but what I have on my desk is actual silicon, which
expects timers to have a nominal value (and I expect this is the
case for most people).

Making sure the FAST_LINK_MODE bit is cleared when configuring the RC
solves this problem.

Fixes: 9c0ef6d34fdb ("PCI: amlogic: Add the Amlogic Meson PCIe controller driver")
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 drivers/pci/controller/dwc/pci-meson.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/controller/dwc/pci-meson.c b/drivers/pci/controller/dwc/pci-meson.c
index 3715dceca1bf..ca59ba9e0ecd 100644
--- a/drivers/pci/controller/dwc/pci-meson.c
+++ b/drivers/pci/controller/dwc/pci-meson.c

@@ -289,11 +289,11 @@ static void meson_pcie_init_dw(struct meson_pcie *mp)
 meson_cfg_writel(mp, val, PCIE_CFG0);
 
 val = meson_elb_readl(mp, PCIE_PORT_LINK_CTRL_OFF);
- val &= ~LINK_CAPABLE_MASK;
+ val &= ~(LINK_CAPABLE_MASK | FAST_LINK_MODE);
 meson_elb_writel(mp, val, PCIE_PORT_LINK_CTRL_OFF);
 
 val = meson_elb_readl(mp, PCIE_PORT_LINK_CTRL_OFF);
- val |= LINK_CAPABLE_X1 | FAST_LINK_MODE;
+ val |= LINK_CAPABLE_X1;
 meson_elb_writel(mp, val, PCIE_PORT_LINK_CTRL_OFF);
 
 val = meson_elb_readl(mp, PCIE_GEN2_CTRL_OFF);

 
Yue, Kevin: any comment on this?
 
I found that the issue is reproducible even without a PCIe switch,
depending on the single device I plug in this machine (an Intel SSD
works fine, while a Marvell Ethernet adapter never shows up) as the
LTSSM times out much earlier than it really should (HW timers running
too quickly). Applying this patch makes every single device I have
lying around work fine.
 
Thanks,
 
M.
-- 
Jazz is not dead. It just smells funny...
 
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-- 
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