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Message-ID: <7dbb0d8b-3708-60ba-ee9e-78aa48bee160@linux.intel.com>
Date: Thu, 13 Feb 2025 15:52:05 +0200 (EET)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Bjorn Helgaas <helgaas@...nel.org>
cc: Alex Williamson <alex.williamson@...hat.com>,
Christian König <ckoenig.leichtzumerken@...il.com>,
linux-pci@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH 1/2] PCI: Avoid pointless capability searches
On Fri, 7 Feb 2025, Bjorn Helgaas wrote:
> From: Bjorn Helgaas <bhelgaas@...gle.com>
>
> Many of the save/restore functions in the pci_save_state() and
> pci_restore_state() paths depend on both a PCI capability of the device and
> a pci_cap_saved_state structure to hold the configuration data, and they
> skip the operation if either is missing.
>
> Look for the pci_cap_saved_state first so if we don't have one, we can skip
> searching for the device capability, which requires several slow config
> space accesses.
>
> Remove some error messages if the pci_cap_saved_state is not found so we
> don't complain about having no saved state for a capability the device
> doesn't have. We have already warned in pci_allocate_cap_save_buffers() if
> the capability is present but we were unable to allocate a buffer.
>
> Other than the message change, no functional change intended.
>
> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
> ---
> drivers/pci/pci.c | 27 ++++++++++++++-------------
> drivers/pci/pcie/aspm.c | 15 ++++++++-------
> drivers/pci/vc.c | 22 +++++++++++-----------
> 3 files changed, 33 insertions(+), 31 deletions(-)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 869d204a70a3..503376bf7e75 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -1686,10 +1686,8 @@ static int pci_save_pcie_state(struct pci_dev *dev)
> return 0;
>
> save_state = pci_find_saved_cap(dev, PCI_CAP_ID_EXP);
> - if (!save_state) {
> - pci_err(dev, "buffer not found in %s\n", __func__);
> + if (!save_state)
> return -ENOMEM;
> - }
>
> cap = (u16 *)&save_state->cap.data[0];
> pcie_capability_read_word(dev, PCI_EXP_DEVCTL, &cap[i++]);
> @@ -1742,19 +1740,17 @@ static void pci_restore_pcie_state(struct pci_dev *dev)
>
> static int pci_save_pcix_state(struct pci_dev *dev)
> {
> - int pos;
> struct pci_cap_saved_state *save_state;
> + u8 pos;
> +
> + save_state = pci_find_saved_cap(dev, PCI_CAP_ID_PCIX);
> + if (!save_state)
> + return -ENOMEM;
>
> pos = pci_find_capability(dev, PCI_CAP_ID_PCIX);
> if (!pos)
> return 0;
>
> - save_state = pci_find_saved_cap(dev, PCI_CAP_ID_PCIX);
> - if (!save_state) {
> - pci_err(dev, "buffer not found in %s\n", __func__);
> - return -ENOMEM;
> - }
> -
> pci_read_config_word(dev, pos + PCI_X_CMD,
> (u16 *)save_state->cap.data);
>
> @@ -1763,14 +1759,19 @@ static int pci_save_pcix_state(struct pci_dev *dev)
>
> static void pci_restore_pcix_state(struct pci_dev *dev)
> {
> - int i = 0, pos;
> struct pci_cap_saved_state *save_state;
> + u8 pos;
> + int i = 0;
> u16 *cap;
>
> save_state = pci_find_saved_cap(dev, PCI_CAP_ID_PCIX);
> - pos = pci_find_capability(dev, PCI_CAP_ID_PCIX);
> - if (!save_state || !pos)
> + if (!save_state)
> return;
> +
> + pos = pci_find_capability(dev, PCI_CAP_ID_PCIX);
> + if (!pos)
> + return;
> +
> cap = (u16 *)&save_state->cap.data[0];
>
> pci_write_config_word(dev, pos + PCI_X_CMD, cap[i++]);
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index e0bc90597dca..007e4a082e6f 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -35,16 +35,14 @@ void pci_save_ltr_state(struct pci_dev *dev)
> if (!pci_is_pcie(dev))
> return;
>
> + save_state = pci_find_saved_ext_cap(dev, PCI_EXT_CAP_ID_LTR);
> + if (!save_state)
> + return;
> +
> ltr = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_LTR);
> if (!ltr)
> return;
>
> - save_state = pci_find_saved_ext_cap(dev, PCI_EXT_CAP_ID_LTR);
> - if (!save_state) {
> - pci_err(dev, "no suspend buffer for LTR; ASPM issues possible after resume\n");
> - return;
> - }
> -
> /* Some broken devices only support dword access to LTR */
> cap = &save_state->cap.data[0];
> pci_read_config_dword(dev, ltr + PCI_LTR_MAX_SNOOP_LAT, cap);
> @@ -57,8 +55,11 @@ void pci_restore_ltr_state(struct pci_dev *dev)
> u32 *cap;
>
> save_state = pci_find_saved_ext_cap(dev, PCI_EXT_CAP_ID_LTR);
> + if (!save_state)
> + return;
> +
> ltr = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_LTR);
> - if (!save_state || !ltr)
> + if (!ltr)
> return;
>
> /* Some broken devices only support dword access to LTR */
> diff --git a/drivers/pci/vc.c b/drivers/pci/vc.c
> index a4ff7f5f66dd..c39f3be518d4 100644
> --- a/drivers/pci/vc.c
> +++ b/drivers/pci/vc.c
> @@ -355,20 +355,17 @@ int pci_save_vc_state(struct pci_dev *dev)
> int i;
>
> for (i = 0; i < ARRAY_SIZE(vc_caps); i++) {
> - int pos, ret;
> struct pci_cap_saved_state *save_state;
> + int pos, ret;
> +
> + save_state = pci_find_saved_ext_cap(dev, vc_caps[i].id);
> + if (!save_state)
> + return -ENOMEM;
>
> pos = pci_find_ext_capability(dev, vc_caps[i].id);
> if (!pos)
> continue;
>
> - save_state = pci_find_saved_ext_cap(dev, vc_caps[i].id);
> - if (!save_state) {
> - pci_err(dev, "%s buffer not found in %s\n",
> - vc_caps[i].name, __func__);
> - return -ENOMEM;
> - }
I think this order change will cause a functional change because
pci_allocate_vc_save_buffers() only allocated for those capabilities that
are exist for dev. Thus, the loop will prematurely exit.
> -
> ret = pci_vc_do_save_buffer(dev, pos, save_state, true);
> if (ret) {
> pci_err(dev, "%s save unsuccessful %s\n",
> @@ -392,12 +389,15 @@ void pci_restore_vc_state(struct pci_dev *dev)
> int i;
>
> for (i = 0; i < ARRAY_SIZE(vc_caps); i++) {
> - int pos;
> struct pci_cap_saved_state *save_state;
> + int pos;
> +
> + save_state = pci_find_saved_ext_cap(dev, vc_caps[i].id);
> + if (!save_state)
> + continue;
>
> pos = pci_find_ext_capability(dev, vc_caps[i].id);
> - save_state = pci_find_saved_ext_cap(dev, vc_caps[i].id);
> - if (!save_state || !pos)
> + if (!pos)
> continue;
>
> pci_vc_do_save_buffer(dev, pos, save_state, false);
>
--
i.
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