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Message-ID: <20210930233339.GA924309@bhelgaas>
Date: Thu, 30 Sep 2021 18:33:39 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: "Saheed O. Bolarinwa" <refactormyself@...il.com>
Cc: linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v3 1/3] PCI/ASPM: Do not cache link latencies
On Wed, Sep 29, 2021 at 02:41:14AM +0200, Saheed O. Bolarinwa wrote:
> The latencies of the upstream and downstream are calculated within
> pcie_aspm_cap_init() and cached in struct pcie_link_state.latency_*
> These values are only used in pcie_aspm_check_latency() where they are
> compared with the acceptable latencies on the link.
>
> This patch:
> - removes `latency_*` entries from struct pcie_link_state.
> - calculates the latencies directly where they are needed.
> - moves pci_function_0() upward, so that the downstream device can be
> obtained by calling it directly.
Ideally I would put the move in its own preliminary patch so the
important parts of this patch are more visible.
> - further removes dependencies on struct pcie_link_state.
>
> Signed-off-by: Saheed O. Bolarinwa <refactormyself@...il.com>
> ---
> drivers/pci/pcie/aspm.c | 54 ++++++++++++++++++++++-------------------
> 1 file changed, 29 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index 013a47f587ce..9e85dfc56657 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -66,9 +66,6 @@ struct pcie_link_state {
> u32 clkpm_default:1; /* Default Clock PM state by BIOS */
> u32 clkpm_disable:1; /* Clock PM disabled */
>
> - /* Exit latencies */
> - struct aspm_latency latency_up; /* Upstream direction exit latency */
> - struct aspm_latency latency_dw; /* Downstream direction exit latency */
> /*
> * Endpoint acceptable latencies. A pcie downstream port only
> * has one slot under it, so at most there are 8 functions.
> @@ -376,9 +373,25 @@ static void encode_l12_threshold(u32 threshold_us, u32 *scale, u32 *value)
> }
> }
>
> +/*
> + * The L1 PM substate capability is only implemented in function 0 in a
> + * multi function device.
> + */
> +static struct pci_dev *pci_function_0(struct pci_bus *linkbus)
> +{
> + struct pci_dev *child;
> +
> + list_for_each_entry(child, &linkbus->devices, bus_list)
> + if (PCI_FUNC(child->devfn) == 0)
> + return child;
> + return NULL;
> +}
> +
> static void pcie_aspm_check_latency(struct pci_dev *endpoint)
> {
> - u32 latency, l1_switch_latency = 0;
> + u32 latency, lnkcap_up, lnkcap_dw, l1_switch_latency = 0;
> + struct pci_dev *downstream;
> + struct aspm_latency latency_up, latency_dw;
> struct aspm_latency *acceptable;
> struct pcie_link_state *link;
>
> @@ -388,17 +401,26 @@ static void pcie_aspm_check_latency(struct pci_dev *endpoint)
> return;
>
> link = endpoint->bus->self->link_state;
> + downstream = pci_function_0(link->pdev->subordinate);
This looks like it's in the wrong patch. Isn't "downstream" still the
same as link->downstream? I think you have another patch that removes
pcie_link_state.downstream, and this hunk should go in that patch.
> acceptable = &link->acceptable[PCI_FUNC(endpoint->devfn)];
>
> while (link) {
> + /* Read direction exit latencies */
> + pcie_capability_read_dword(link->pdev, PCI_EXP_LNKCAP, &lnkcap_up);
> + pcie_capability_read_dword(downstream, PCI_EXP_LNKCAP, &lnkcap_dw);
> + latency_up.l0s = calc_l0s_latency(lnkcap_up);
> + latency_up.l1 = calc_l1_latency(lnkcap_up);
> + latency_dw.l0s = calc_l0s_latency(lnkcap_dw);
> + latency_dw.l1 = calc_l1_latency(lnkcap_dw);
I like this a lot.
> /* Check upstream direction L0s latency */
> if ((link->aspm_capable & ASPM_STATE_L0S_UP) &&
> - (link->latency_up.l0s > acceptable->l0s))
> + (latency_up.l0s > acceptable->l0s))
> link->aspm_capable &= ~ASPM_STATE_L0S_UP;
>
> /* Check downstream direction L0s latency */
> if ((link->aspm_capable & ASPM_STATE_L0S_DW) &&
> - (link->latency_dw.l0s > acceptable->l0s))
> + (latency_dw.l0s > acceptable->l0s))
> link->aspm_capable &= ~ASPM_STATE_L0S_DW;
> /*
> * Check L1 latency.
> @@ -413,7 +435,7 @@ static void pcie_aspm_check_latency(struct pci_dev *endpoint)
> * L1 exit latencies advertised by a device include L1
> * substate latencies (and hence do not do any check).
> */
> - latency = max_t(u32, link->latency_up.l1, link->latency_dw.l1);
> + latency = max_t(u32, latency_up.l1, latency_dw.l1);
> if ((link->aspm_capable & ASPM_STATE_L1) &&
> (latency + l1_switch_latency > acceptable->l1))
> link->aspm_capable &= ~ASPM_STATE_L1;
> @@ -423,20 +445,6 @@ static void pcie_aspm_check_latency(struct pci_dev *endpoint)
> }
> }
>
> -/*
> - * The L1 PM substate capability is only implemented in function 0 in a
> - * multi function device.
> - */
> -static struct pci_dev *pci_function_0(struct pci_bus *linkbus)
> -{
> - struct pci_dev *child;
> -
> - list_for_each_entry(child, &linkbus->devices, bus_list)
> - if (PCI_FUNC(child->devfn) == 0)
> - return child;
> - return NULL;
> -}
> -
> static void pci_clear_and_set_dword(struct pci_dev *pdev, int pos,
> u32 clear, u32 set)
> {
> @@ -593,8 +601,6 @@ static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
> link->aspm_enabled |= ASPM_STATE_L0S_UP;
> if (parent_lnkctl & PCI_EXP_LNKCTL_ASPM_L0S)
> link->aspm_enabled |= ASPM_STATE_L0S_DW;
> - link->latency_up.l0s = calc_l0s_latency(parent_lnkcap);
> - link->latency_dw.l0s = calc_l0s_latency(child_lnkcap);
>
> /* Setup L1 state */
> if (parent_lnkcap & child_lnkcap & PCI_EXP_LNKCAP_ASPM_L1)
> @@ -602,8 +608,6 @@ static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
>
> if (parent_lnkctl & child_lnkctl & PCI_EXP_LNKCTL_ASPM_L1)
> link->aspm_enabled |= ASPM_STATE_L1;
> - link->latency_up.l1 = calc_l1_latency(parent_lnkcap);
> - link->latency_dw.l1 = calc_l1_latency(child_lnkcap);
>
> /* Setup L1 substate */
> pci_read_config_dword(parent, parent->l1ss + PCI_L1SS_CAP,
> --
> 2.20.1
>
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