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Message-ID: <20230128182624.GA1412510@bhelgaas>
Date: Sat, 28 Jan 2023 12:26:24 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Vidya Sagar <vidyas@...dia.com>
Cc: bhelgaas@...gle.com, sathyanarayanan.kuppuswamy@...ux.intel.com,
rafael.j.wysocki@...el.com, kai.heng.feng@...onical.com,
linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
treding@...dia.com, jonathanh@...dia.com, kthota@...dia.com,
mmaddireddy@...dia.com, sagar.tv@...il.com
Subject: Re: [PATCH V1] PCI/ASPM: Update saved buffers with latest ASPM
configuration
On Wed, Jan 25, 2023 at 07:08:30PM +0530, Vidya Sagar wrote:
> Many PCIe device drivers save the configuration state of their respective
> devices during probe and restore the same when their 'slot_reset' hook
> is called through PCIe Error Recovery System.
This strategy of simply restoring config space after a reset is
common, but I think it's only a 90% solution.
After reset, the device is basically in a "fresh poweron" state [1].
At boot-time or for a hot-added device, we do a lot of setup when we
enumerate the device, and assuming that:
- device reset, plus
- current state in the struct pci_dev, plus
- restoring config space
gets all the device and kernel state to the same place is a pretty big
assumption.
That said, we're pretty invested in this strategy for now, and I think
what you propose here is definitely an improvement. Minor comments on
the implementation below.
Bjorn
[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/PCI/pci-error-recovery.rst?id=v6.1#n277
> If the system has a change in ASPM policy after the driver's probe is
> called and before error event occurred, 'slot_reset' hook restores the
> PCIe configuration state to what it was at the time of probe but not with
> what it was just before the occurrence of the error event.
> This effectively leads to a mismatch in the ASPM configuration between
> the device and its upstream parent device.
> This patch addresses that issue by updating the saved configuration state
> of the device with the latest info whenever there is a change w.r.t ASPM
> policy.
>
> Signed-off-by: Vidya Sagar <vidyas@...dia.com>
> ---
> drivers/pci/pci.h | 4 ++++
> drivers/pci/pcie/aspm.c | 40 ++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 44 insertions(+)
> +++ b/drivers/pci/pci.h
> +void pci_save_aspm_state(struct pci_dev *dev);
> +void pci_restore_aspm_state(struct pci_dev *dev);
This patch only adds calls to these functions in aspm.c, so it doesn't
look like we need declarations here or stubs below.
> +static inline void pci_save_aspm_state(struct pci_dev *dev) { }
> +static inline void pci_restore_aspm_state(struct pci_dev *dev) { }
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index 53a1fa306e1e..f25e0440d36b 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -151,6 +151,7 @@ static void pcie_set_clkpm_nocheck(struct pcie_link_state *link, int enable)
> PCI_EXP_LNKCTL_CLKREQ_EN,
> val);
> link->clkpm_enabled = !!enable;
> + pci_save_aspm_state(child);
> }
>
> static void pcie_set_clkpm(struct pcie_link_state *link, int enable)
> @@ -757,6 +758,39 @@ static void pcie_config_aspm_l1ss(struct pcie_link_state *link, u32 state)
> PCI_L1SS_CTL1_L1SS_MASK, val);
> }
>
> +void pci_save_aspm_state(struct pci_dev *dev)
I might be missing something because these look like they should be
static. But the declarations and these being non-static suggest that
you might have something more in mind that isn't part of this patch?
Move these save-state functions higher up if necessary to resolve the
forward reference from pcie_set_clkpm_nocheck().
> +{
> + int i = 0;
> + struct pci_cap_saved_state *save_state;
> + u16 *cap;
> +
> + if (!pci_is_pcie(dev))
> + return;
> +
> + save_state = pci_find_saved_cap(dev, PCI_CAP_ID_EXP);
> + if (!save_state)
> + return;
> +
> + cap = (u16 *)&save_state->cap.data[0];
> + i++;
"i" looks unnecessary, but I guess I see what you're doing --
mirroring the structure of pci_save_pcie_state() to make sure we put
LNKCTL in the correct element of cap[].
> + pcie_capability_read_word(dev, PCI_EXP_LNKCTL, &cap[i++]);
> +}
> +
> +void pci_restore_aspm_state(struct pci_dev *dev)
No callers for this? And I don't see why you would *need* callers;
this should be restored by pci_restore_pcie_state() already. So this
looks like it could be removed completely.
> +{
> + int i = 0;
> + struct pci_cap_saved_state *save_state;
> + u16 *cap;
> +
> + save_state = pci_find_saved_cap(dev, PCI_CAP_ID_EXP);
> + if (!save_state)
> + return;
> +
> + cap = (u16 *)&save_state->cap.data[0];
> + i++;
> + pcie_capability_write_word(dev, PCI_EXP_LNKCTL, cap[i++]);
> +}
> +
> void pci_save_aspm_l1ss_state(struct pci_dev *dev)
> {
> struct pci_cap_saved_state *save_state;
> @@ -849,6 +883,12 @@ static void pcie_config_aspm_link(struct pcie_link_state *link, u32 state)
> pcie_config_aspm_dev(parent, upstream);
>
> link->aspm_enabled = state;
> +
> + /* Update latest ASPM configuration in saved context */
> + pci_save_aspm_state(link->downstream);
> + pci_save_aspm_l1ss_state(link->downstream);
> + pci_save_aspm_state(parent);
> + pci_save_aspm_l1ss_state(parent);
> }
>
> static void pcie_config_aspm_path(struct pcie_link_state *link)
> --
> 2.17.1
>
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