On Mon, Jun 9, 2025 at 1:03 AM Hongxing Zhu <hongxing.zhu@xxxxxxx> wrote:
>
> > -----Original Message-----
> > From: Tim Harvey <tharvey@xxxxxxxxxxxxx>
> > Sent: 2025年6月7日 5:04
> > To: Hongxing Zhu <hongxing.zhu@xxxxxxx>
> > Cc: l.stach@xxxxxxxxxxxxxx; bhelgaas@xxxxxxxxxx; lpieralisi@xxxxxxxxxx;
> > kw@xxxxxxxxx; manivannan.sadhasivam@xxxxxxxxxx; robh@xxxxxxxxxx;
> > krzk+dt@xxxxxxxxxx; conor+dt@xxxxxxxxxx; shawnguo@xxxxxxxxxx; Frank Li
> > <frank.li@xxxxxxx>; s.hauer@xxxxxxxxxxxxxx; festevam@xxxxxxxxx;
> > imx@xxxxxxxxxxxxxxx; kernel@xxxxxxxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx;
> > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx;
> > linux-kernel@xxxxxxxxxxxxxxx
> > 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@xxxxxxx>
> > 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@xxxxxxx>
> > > Reviewed-by: Manivannan Sadhasivam
> > <manivannan.sadhasivam@xxxxxxxxxx>
> > > Reviewed-by: Frank Li <Frank.Li@xxxxxxx>
> > > ---
> > > 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.
>
Hi Richard,
Thanks for your quick response. Do you mean not correct for newer IP
core in i.MX8MM/i.MX8MP or in the case of a bridge?
> 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);
>
Yes this resolves the regression of failing to reliably enumerate
downstream devices. I think that should be submitted with a fixes tag.
The i.MX8MP+PI7C9X2G608GP switch hanging issue was hardware related...
i was sadly testing on an old board with a defect. I did previously
have a hang issue there discussed previously here [1] but it was
resolved with commit 9c03e30e3ade ("PCI: imx6: Skip link up workaround
for newer platforms").
How much testing is done with i.MX8M{M,P} board with a switch? I feel
like I'm the only one with these SoC's and a switch and I need to get
better at monitoring patches to the IMX6 PCI controller driver and
testing these scenarios.
Best Regards,
Tim
[1] https://www.spinics.net/lists/linux-pci/msg142764.html
> > 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
