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Message-ID: <20250221022008.69533-1-enjuk@amazon.com>
Date: Fri, 21 Feb 2025 11:20:08 +0900
From: Kohei Enju <enjuk@...zon.com>
To: <helgaas@...nel.org>
CC: <alex.williamson@...hat.com>, <bhelgaas@...gle.com>,
<ckoenig.leichtzumerken@...il.com>, <ilpo.jarvinen@...ux.intel.com>,
<linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>,
<takamitz@...zon.co.jp>, <kuniyu@...zon.com>, <kohei.enju@...il.com>
Subject: Re: [PATCH v2 1/2] PCI: Avoid pointless capability searches
> 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 ++++++++-------
> 2 files changed, 22 insertions(+), 20 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;
> - }
When devices don't have PCI_CAP_ID_PCIX, this change in order appears to
cause a functional change.
Since probe functions of some drivers (e.g. Intel e1000) rely on the return
value, I think they fail after that change in this situation.
Actually in my QEMU VM, e1000 driver failed to probe the device due to
-ENOMEM from pci_save_pcix_state().
```
[root@...alhost ~]# dmesg | grep e1000
[ 0.400303] [ T1] e1000: Intel(R) PRO/1000 Network Driver
[ 0.400805] [ T1] e1000: Copyright (c) 1999-2006 Intel Corporation.
[ 0.710970] [ T1] e1000 0000:00:03.0: probe with driver e1000 failed with error -12
[root@...alhost ~]# lspci -nnvs 00:03.0
00:03.0 Ethernet controller [0200]: Intel Corporation 82540EM Gigabit Ethernet Controller [8086:100e] (rev 03)
Subsystem: Red Hat, Inc. QEMU Virtual Machine [1af4:1100]
Flags: fast devsel, IRQ 11
Memory at febc0000 (32-bit, non-prefetchable) [size=128K]
I/O ports at c000 [size=64]
Expansion ROM at feb80000 [disabled] [size=256K]
lspci: Unable to load libkmod resources: error -2
```
Regarding pci_save_vc_state(), I found that similar comments were provided in
this context:
https://lore.kernel.org/all/7dbb0d8b-3708-60ba-ee9e-78aa48bee160@linux.intel.com/
However, the same type of order change is still left in
pci_save_pcix_state().
> -
> 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 */
> --
> 2.34.1
Regards,
Kohei
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