Re: [PATCH v2] rtw88: Disable PCIe ASPM while doing NAPI poll on 8821CE

[Kai-Heng Feng]

On Tue, Dec 14, 2021 at 1:59 PM Pkshih <pkshih@xxxxxxxxxxx> wrote:
>
>
> > -----Original Message-----
> > From: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>
> > Sent: Tuesday, December 14, 2021 1:33 PM
> > To: tony0620emma@xxxxxxxxx; Pkshih <pkshih@xxxxxxxxxxx>
> > Cc: jian-hong@xxxxxxxxxxxx; Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>; Kalle Valo
> > <kvalo@xxxxxxxxxxxxxx>; David S. Miller <davem@xxxxxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>; Bernie
> > Huang <phhuang@xxxxxxxxxxx>; Brian Norris <briannorris@xxxxxxxxxxxx>; linux-wireless@xxxxxxxxxxxxxxx;
> > netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> > Subject: [PATCH v2] rtw88: Disable PCIe ASPM while doing NAPI poll on 8821CE
> >
> > Many Intel based platforms face system random freeze after commit
> > 9e2fd29864c5 ("rtw88: add napi support").
> >
> > The commit itself shouldn't be the culprit. My guess is that the 8821CE
> > only leaves ASPM L1 for a short period when IRQ is raised. Since IRQ is
> > masked during NAPI polling, the PCIe link stays at L1 and makes RX DMA
> > extremely slow. Eventually the RX ring becomes messed up:
> > [ 1133.194697] rtw_8821ce 0000:02:00.0: pci bus timeout, check dma status
> >
> > Since the 8821CE hardware may fail to leave ASPM L1, manually do it in
> > the driver to resolve the issue.
> >
> > Fixes: 9e2fd29864c5 ("rtw88: add napi support")
> > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=215131
> > BugLink: https://bugs.launchpad.net/bugs/1927808
> > Signed-off-by: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>
> > ---
> > v2:
> >  - Add default value for module parameter.
> >
> >  drivers/net/wireless/realtek/rtw88/pci.c | 74 ++++++++----------------
> >  drivers/net/wireless/realtek/rtw88/pci.h |  1 +
> >  2 files changed, 24 insertions(+), 51 deletions(-)
> >
> > diff --git a/drivers/net/wireless/realtek/rtw88/pci.c b/drivers/net/wireless/realtek/rtw88/pci.c
> > index 3b367c9085eba..4ab75ac2500e9 100644
> > --- a/drivers/net/wireless/realtek/rtw88/pci.c
> > +++ b/drivers/net/wireless/realtek/rtw88/pci.c
> > @@ -2,7 +2,6 @@
> >  /* Copyright(c) 2018-2019  Realtek Corporation
> >   */
> >
> > -#include <linux/dmi.h>
> >  #include <linux/module.h>
> >  #include <linux/pci.h>
> >  #include "main.h"
> > @@ -16,10 +15,13 @@
> >
> >  static bool rtw_disable_msi;
> >  static bool rtw_pci_disable_aspm;
> > +static int rtw_rx_aspm = -1;
> >  module_param_named(disable_msi, rtw_disable_msi, bool, 0644);
> >  module_param_named(disable_aspm, rtw_pci_disable_aspm, bool, 0644);
> > +module_param_named(rx_aspm, rtw_rx_aspm, int, 0444);
> >  MODULE_PARM_DESC(disable_msi, "Set Y to disable MSI interrupt support");
> >  MODULE_PARM_DESC(disable_aspm, "Set Y to disable PCI ASPM support");
> > +MODULE_PARM_DESC(rx_aspm, "Use PCIe ASPM for RX (0=disable, 1=enable, -1=default)");
> >
> >  static u32 rtw_pci_tx_queue_idx_addr[] = {
> >       [RTW_TX_QUEUE_BK]       = RTK_PCI_TXBD_IDX_BKQ,
> > @@ -1409,7 +1411,11 @@ static void rtw_pci_link_ps(struct rtw_dev *rtwdev, bool enter)
> >        * throughput. This is probably because the ASPM behavior slightly
> >        * varies from different SOC.
> >        */
> > -     if (rtwpci->link_ctrl & PCI_EXP_LNKCTL_ASPM_L1)
> > +     if (!(rtwpci->link_ctrl & PCI_EXP_LNKCTL_ASPM_L1))
> > +             return;
> > +
> > +     if ((enter && atomic_dec_return(&rtwpci->link_usage) == 0) ||
> > +         (!enter && atomic_inc_return(&rtwpci->link_usage) == 1))
> >               rtw_pci_aspm_set(rtwdev, enter);
> >  }
> >
>
> I found calling pci_link_ps isn't always symmetric, so we need to reset
> ref_cnt at pci_start() like below, or we can't enter rtw_pci_aspm_set()
> anymore. The negative flow I face is
> ifup -> connect AP -> ifdown -> ifup (ref_cnt isn't expected now).

Is it expected to be asymmetric?
If it's intended to be this way, I'll change where we set link_usage.
Otherwise I think making it symmetric makes more sense.

Kai-Heng

>
>
> @@ -582,6 +582,8 @@ static int rtw_pci_start(struct rtw_dev *rtwdev)
>         rtw_pci_napi_start(rtwdev);
>
>         spin_lock_bh(&rtwpci->irq_lock);
> +       atomic_set(&rtwpci->link_usage, 1);
>         rtwpci->running = true;
>         rtw_pci_enable_interrupt(rtwdev, rtwpci, false);
>         spin_unlock_bh(&rtwpci->irq_lock);
>
> --
> Ping-Ke
>
>