RE: [PATCH net-next 2/3] r8169: enable RTL8168H/RTL8168EP/RTL8168FP/RTL8125/RTL8126 LTR support

[Hau <hau@realtek.com>]

> -----Original Message-----
> From: Heiner Kallweit [mailto:hkallweit1@gmail.com]
> Sent: Saturday, March 1, 2025 6:58 AM
> To: Bjorn Helgaas <helgaas@kernel.org>; Hau <hau@realtek.com>
> Cc: nic_swsd <nic_swsd@realtek.com>; andrew+netdev@lunn.ch;
> davem@davemloft.net; edumazet@google.com; kuba@kernel.org;
> pabeni@redhat.com; Bjorn Helgaas <bhelgaas@google.com>;
> netdev@vger.kernel.org; linux-kernel@vger.kernel.org; linux-
> pci@vger.kernel.org
> Subject: Re: [PATCH net-next 2/3] r8169: enable
> RTL8168H/RTL8168EP/RTL8168FP/RTL8125/RTL8126 LTR support
> 
> 
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> 
> On 24.02.2025 20:00, Bjorn Helgaas wrote:
> > On Mon, Feb 24, 2025 at 04:33:50PM +0000, Hau wrote:
> >>> On 21.02.2025 08:18, ChunHao Lin wrote:
> >>>> This patch will enable
> RTL8168H/RTL8168EP/RTL8168FP/RTL8125/RTL8126
> >>>> LTR support on the platforms that have tested with LTR enabled.
> >>>
> >>> Where in the code is the check whether platform has been tested with
> LTR?
> >>>
> >> LTR is for L1,2. But L1 will be disabled when rtl_aspm_is_safe()
> >> return false. So LTR needs rtl_aspm_is_safe() to return true.
> >>
> >>>> Signed-off-by: ChunHao Lin <hau@realtek.com>
> >>>> ---
> >>>>  drivers/net/ethernet/realtek/r8169_main.c | 108
> >>>> ++++++++++++++++++++++
> >>>>  1 file changed, 108 insertions(+)
> >>>>
> >>>> diff --git a/drivers/net/ethernet/realtek/r8169_main.c
> >>>> b/drivers/net/ethernet/realtek/r8169_main.c
> >>>> index 731302361989..9953eaa01c9d 100644
> >>>> --- a/drivers/net/ethernet/realtek/r8169_main.c
> >>>> +++ b/drivers/net/ethernet/realtek/r8169_main.c
> >>>> @@ -2955,6 +2955,111 @@ static void rtl_disable_exit_l1(struct
> >>> rtl8169_private *tp)
> >>>>       }
> >>>>  }
> >>>>
> >>>> +static void rtl_set_ltr_latency(struct rtl8169_private *tp) {
> >>>> +     switch (tp->mac_version) {
> >>>> +     case RTL_GIGA_MAC_VER_70:
> >>>> +     case RTL_GIGA_MAC_VER_71:
> >>>> +             r8168_mac_ocp_write(tp, 0xcdd0, 0x9003);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdd2, 0x8c09);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdd8, 0x9003);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdd4, 0x9003);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdda, 0x9003);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdd6, 0x9003);
> >>>> +             r8168_mac_ocp_write(tp, 0xcddc, 0x9003);
> >>>> +             r8168_mac_ocp_write(tp, 0xcde8, 0x887a);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdea, 0x9003);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdec, 0x8c09);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdee, 0x9003);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdf0, 0x8a62);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdf2, 0x9003);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdf4, 0x883e);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdf6, 0x9003);
> >>>> +             break;
> >>>> +     case RTL_GIGA_MAC_VER_61 ... RTL_GIGA_MAC_VER_66:
> >>>> +             r8168_mac_ocp_write(tp, 0xcdd0, 0x9003);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdd2, 0x889c);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdd8, 0x9003);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdd4, 0x8c30);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdda, 0x9003);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdd6, 0x9003);
> >>>> +             r8168_mac_ocp_write(tp, 0xcddc, 0x9003);
> >>>> +             r8168_mac_ocp_write(tp, 0xcde8, 0x883e);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdea, 0x9003);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdec, 0x889c);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdee, 0x9003);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdf0, 0x8C09);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdf2, 0x9003);
> >>>> +             break;
> >>>> +     case RTL_GIGA_MAC_VER_46 ... RTL_GIGA_MAC_VER_53:
> >>>> +             r8168_mac_ocp_write(tp, 0xcdd8, 0x9003);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdda, 0x9003);
> >>>> +             r8168_mac_ocp_write(tp, 0xcddc, 0x9003);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdd2, 0x883c);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdd4, 0x8c12);
> >>>> +             r8168_mac_ocp_write(tp, 0xcdd6, 0x9003);
> >>>> +             break;
> >>>> +     default:
> >>>> +             break;
> >>>> +     }
> >>>> +}
> >>>> +
> >>>> +static void rtl_reset_pci_ltr(struct rtl8169_private *tp) {
> >>>> +     struct pci_dev *pdev = tp->pci_dev;
> >>>> +     u16 cap;
> >>>> +
> >>>> +     pcie_capability_read_word(pdev, PCI_EXP_DEVCTL2, &cap);
> >>>> +     if (cap & PCI_EXP_DEVCTL2_LTR_EN) {
> >>>> +             pcie_capability_clear_word(pdev, PCI_EXP_DEVCTL2,
> >>>> +                                        PCI_EXP_DEVCTL2_LTR_EN);
> >>>> +             pcie_capability_set_word(pdev, PCI_EXP_DEVCTL2,
> >>>> +                                      PCI_EXP_DEVCTL2_LTR_EN);
> >>>
> >>> I'd prefer that only PCI core deals with these registers (functions
> >>> like pci_configure_ltr()). Any specific reason for this reset? Is it
> >>> something which could be applicable for other devices too, so that
> >>> the PCI core should be extended?
> >>>
> >> It is for specific platform. On that platform driver needs to do this
> >> to let LTR works.
> >
> I interpret this in a way that the chip triggers some internal LTR configuration
> activity if it detects bit PCI_EXP_DEVCTL2_LTR_EN changing from 0 to 1. And
> this needed activity isn't triggered if PCI_EXP_DEVCTL2_LTR_EN is set already
> and doesn't change.
> Hau, is this correct?
> 
It may be the reason for the LTR  of these platforms to work. But I will remove this
quirk from next version  patch.

> So the PCI_EXP_DEVCTL2_LTR_EN reset is some kind of needed quirk.
> However PCI quirks are applied too early, before we even detected the chip
> version in probe(). Therefore I also think a helper for this reset in PCI core
> would be best.
> 
> And what hasn't been mentioned yet: We have to skip the chip-specific LTR
> configuration if pci_dev->ltr_path isn't set.
> 
I will add checking pci_dev->ltr_path in next version patch.

> > This definitely looks like code that should not be in a driver.
> > Drivers shouldn't need to touch ASPM or LTR configuration unless
> > there's a device defect to work around, and that should use a PCI core
> > interface.  Depending on what the defect is, we may need to add a new
> > interface.
> >
> > This clear/set of PCI_EXP_DEVCTL2_LTR_EN when it was already set could
> > work around some kind of device defect, or it could be a hint that
> > something in the PCI core is broken.  Maybe the core is configuring
> > ASPM/LTR incorrectly.
> >
> > Bjorn