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Message-ID:
<AS8PR04MB8676C1206066A3215DB5F3B78C6BA@AS8PR04MB8676.eurprd04.prod.outlook.com>
Date: Mon, 9 Jun 2025 08:03:16 +0000
From: Hongxing Zhu <hongxing.zhu@....com>
To: "tharvey@...eworks.com" <tharvey@...eworks.com>
CC: "l.stach@...gutronix.de" <l.stach@...gutronix.de>, "bhelgaas@...gle.com"
<bhelgaas@...gle.com>, "lpieralisi@...nel.org" <lpieralisi@...nel.org>,
"kw@...ux.com" <kw@...ux.com>, "manivannan.sadhasivam@...aro.org"
<manivannan.sadhasivam@...aro.org>, "robh@...nel.org" <robh@...nel.org>,
"krzk+dt@...nel.org" <krzk+dt@...nel.org>, "conor+dt@...nel.org"
<conor+dt@...nel.org>, "shawnguo@...nel.org" <shawnguo@...nel.org>, Frank Li
<frank.li@....com>, "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
"festevam@...il.com" <festevam@...il.com>, "imx@...ts.linux.dev"
<imx@...ts.linux.dev>, "kernel@...gutronix.de" <kernel@...gutronix.de>,
"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>, "devicetree@...r.kernel.org"
<devicetree@...r.kernel.org>, "linux-kernel@...r.kernel.org"
<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v7 05/10] PCI: imx6: Deassert apps_reset in
imx_pcie_deassert_core_reset()
> -----Original Message-----
> From: Tim Harvey <tharvey@...eworks.com>
> Sent: 2025年6月7日 5:04
> To: Hongxing Zhu <hongxing.zhu@....com>
> Cc: l.stach@...gutronix.de; bhelgaas@...gle.com; lpieralisi@...nel.org;
> kw@...ux.com; manivannan.sadhasivam@...aro.org; robh@...nel.org;
> krzk+dt@...nel.org; conor+dt@...nel.org; shawnguo@...nel.org; Frank Li
> <frank.li@....com>; s.hauer@...gutronix.de; festevam@...il.com;
> imx@...ts.linux.dev; kernel@...gutronix.de; linux-pci@...r.kernel.org;
> linux-arm-kernel@...ts.infradead.org; devicetree@...r.kernel.org;
> linux-kernel@...r.kernel.org
> Subject: Re: [PATCH v7 05/10] PCI: imx6: Deassert apps_reset in
> imx_pcie_deassert_core_reset()
>
> On Tue, Nov 26, 2024 at 12:03 AM Richard Zhu <hongxing.zhu@....com>
> wrote:
> >
> > Since the apps_reset is asserted in imx_pcie_assert_core_reset(), it
> > should be deasserted in imx_pcie_deassert_core_reset().
> >
> > Fixes: 9b3fe6796d7c ("PCI: imx6: Add code to support i.MX7D")
> > Signed-off-by: Richard Zhu <hongxing.zhu@....com>
> > Reviewed-by: Manivannan Sadhasivam
> <manivannan.sadhasivam@...aro.org>
> > Reviewed-by: Frank Li <Frank.Li@....com>
> > ---
> > drivers/pci/controller/dwc/pci-imx6.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/pci/controller/dwc/pci-imx6.c
> > b/drivers/pci/controller/dwc/pci-imx6.c
> > index 3538440601a7..413db182ce9f 100644
> > --- a/drivers/pci/controller/dwc/pci-imx6.c
> > +++ b/drivers/pci/controller/dwc/pci-imx6.c
> > @@ -776,6 +776,7 @@ static void imx_pcie_assert_core_reset(struct
> > imx_pcie *imx_pcie) static int imx_pcie_deassert_core_reset(struct
> > imx_pcie *imx_pcie) {
> > reset_control_deassert(imx_pcie->pciephy_reset);
> > + reset_control_deassert(imx_pcie->apps_reset);
> >
> > if (imx_pcie->drvdata->core_reset)
> > imx_pcie->drvdata->core_reset(imx_pcie, false);
> > --
> > 2.37.1
> >
> >
>
> Hi Richard,
>
> I've found that this patch causes a regression on i.MX8MM and i.MX8MP
> boards with hotplug capable bridges:
> i.MX8MM+PI7C9X2G404EV (this switch does not support hotplug) - no issues
> i.MX8MM+PI7C9X2G608GP (hotplug) - fails to reliably enumerate
> downstream devices about 80% of the time ^^^ when this occurs
> PCI_PRIMARY_BUS (0x18) for the root complex
> 0000:00:00.0 reads 0x00000000 instead of 0x00ff0100
> (PCI_SECONDARY_BUS is 0 instead of 1 and PCI_SUBBORDINATE_BUS is 0
> instead of 0xff) i.MX8MP+PI7C9X2G608GP (hotplug) - hangs at
> imx_pcie_ltssm_enable deassert apps_reset
>
> In both cases here reverting ef61c7d8d032 ("PCI: imx6: Deassert apps_reset
> in imx_pcie_deassert_core_reset()") resolves this.
>
[Richard Zhu] I'm afraid that the ltssm_en bit assert to 1b'1 in
imx_pcie_deassert_core_reset() is not correct in your use case.
Actually, the apps_reset isn't a real reset. It's the ltssm_en bit.
From this perspective view, It's inappropriate to toggle the ltssm_en bit in
imx_pcie_assert/deassert_core_reset() functions.
I consider to move the apps_reset out of _reset_ functions.
Can you help to test the following changes in you use-case?
--- a/drivers/pci/controller/dwc/pci-imx6.c
+++ b/drivers/pci/controller/dwc/pci-imx6.c
@@ -776,7 +776,6 @@ static int imx7d_pcie_core_reset(struct imx_pcie *imx_pcie, bool assert)
static void imx_pcie_assert_core_reset(struct imx_pcie *imx_pcie)
{
reset_control_assert(imx_pcie->pciephy_reset);
- reset_control_assert(imx_pcie->apps_reset);
if (imx_pcie->drvdata->core_reset)
imx_pcie->drvdata->core_reset(imx_pcie, true);
@@ -788,7 +787,6 @@ static void imx_pcie_assert_core_reset(struct imx_pcie *imx_pcie)
static int imx_pcie_deassert_core_reset(struct imx_pcie *imx_pcie)
{
reset_control_deassert(imx_pcie->pciephy_reset);
- reset_control_deassert(imx_pcie->apps_reset);
if (imx_pcie->drvdata->core_reset)
imx_pcie->drvdata->core_reset(imx_pcie, false);
@@ -1176,6 +1174,9 @@ static int imx_pcie_host_init(struct dw_pcie_rp *pp)
}
}
+ /* Make sure that PCIe LTSSM is cleared */
+ imx_pcie_ltssm_disable(dev);
+
ret = imx_pcie_deassert_core_reset(imx_pcie);
if (ret < 0) {
dev_err(dev, "pcie deassert core reset failed: %d\n", ret);
> I notice the sequence of events here is:
> imx_pcie_assert_core_reset asserts apps_reset (disables LTSSM)
> imx_pcie_deassert_core_reset deasserts apps_reset (enables LTSSM)
> imx_pcie_ltssm_enable deasserts apps_reset (enables LTSSM; this is where it
> hangs on imx8mp)
>
> Is there perhaps some issue with de-asserting this (enabling LTSSM) when it's
> already in this state?
[Richard Zhu]The apps_reset is updated by src driver by regmap_update_bits().
I can't find the exceptions to update one bit, already has the according value.
Best Regards
Richard Zhu
>
> In the case where downstream devices do not enumerate some investigation
> points to them not being happy that the link drops so perhaps deasserting
> apps_reset when its already asserted drops the link and restarts it?
>
> Best Regards,
>
> Tim
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