From: Lukas Wunner <lukas@wunner.de>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: linux-pci@vger.kernel.org, Marco Nenciarini <mnencia@kcore.it>,
Michal Winiarski <michal.winiarski@intel.com>,
Ilpo Jarvinen <ilpo.jarvinen@linux.intel.com>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Eric Chanudet <echanude@redhat.com>,
Jean Guyader <jean.guyader@gmail.com>,
Alex Williamson <alex@shazbot.org>, Sinan Kaya <okaya@kernel.org>
Subject: [PATCH] PCI: Drop unnecessary retries when restoring BARs
Date: Sun, 3 May 2026 15:34:46 +0200 [thread overview]
Message-ID: <785c98b50a7a00d0698848c75d51b8f5669ad18f.1777814679.git.lukas@wunner.de> (raw)
In 2012, commit 26f41062f28d ("PCI: check for pci bar restore completion
and retry") amended pci_restore_state() to attempt BAR restoration up to
10 times. This was necessary because back in the day, only a 100 msec
delay was observed after pcie_flr() carried out a Function Level Reset.
The retries ensured that BARs were restored even if devices needed more
time to come out of reset.
In 2016, commit 5adecf817dd6 ("PCI: Wait for up to 1000ms after FLR
reset") extended the delay to 1 sec. Commit a2758b6b8fdb ("PCI: Rename
pci_flr_wait() to pci_dev_wait() and make it generic") subsequently
extended it further to 60 sec.
The lengthened delay makes it unnecessary to retry BAR restoration, so
drop it.
Reported-by: Bjorn Helgaas <bhelgaas@google.com>
Closes: https://lore.kernel.org/r/20260416225745.GA41850@bhelgaas/
Signed-off-by: Lukas Wunner <lukas@wunner.de>
---
Jesse did ask "why we don't do this delay/check when we perform the FLR
in the first place" when he applied the patch, but nobody followed up
with a patch until Alex did four years later:
https://lore.kernel.org/r/003AAFE53969E14CB1F09B6FD68C3CD409A8B4F2@ORSMSX105.amr.corp.intel.com/
drivers/pci/pci.c | 36 +++++++++++++-----------------------
1 file changed, 13 insertions(+), 23 deletions(-)
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 8f7cfcc..1e386df 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1764,7 +1764,7 @@ int pci_save_state(struct pci_dev *dev)
EXPORT_SYMBOL(pci_save_state);
static void pci_restore_config_dword(struct pci_dev *pdev, int offset,
- u32 saved_val, int retry, bool force)
+ u32 saved_val, bool force)
{
u32 val;
@@ -1772,52 +1772,42 @@ static void pci_restore_config_dword(struct pci_dev *pdev, int offset,
if (!force && val == saved_val)
return;
- for (;;) {
- pci_dbg(pdev, "restore config %#04x: %#010x -> %#010x\n",
- offset, val, saved_val);
- pci_write_config_dword(pdev, offset, saved_val);
- if (retry-- <= 0)
- return;
+ pci_dbg(pdev, "restore config %#04x: %#010x -> %#010x\n", offset, val,
+ saved_val);
- pci_read_config_dword(pdev, offset, &val);
- if (val == saved_val)
- return;
-
- mdelay(1);
- }
+ pci_write_config_dword(pdev, offset, saved_val);
}
static void pci_restore_config_space_range(struct pci_dev *pdev,
- int start, int end, int retry,
- bool force)
+ int start, int end, bool force)
{
int index;
for (index = end; index >= start; index--)
pci_restore_config_dword(pdev, 4 * index,
pdev->saved_config_space[index],
- retry, force);
+ force);
}
static void pci_restore_config_space(struct pci_dev *pdev)
{
if (pdev->hdr_type == PCI_HEADER_TYPE_NORMAL) {
- pci_restore_config_space_range(pdev, 10, 15, 0, false);
+ pci_restore_config_space_range(pdev, 10, 15, false);
/* Restore BARs before the command register. */
- pci_restore_config_space_range(pdev, 4, 9, 10, false);
- pci_restore_config_space_range(pdev, 0, 3, 0, false);
+ pci_restore_config_space_range(pdev, 4, 9, false);
+ pci_restore_config_space_range(pdev, 0, 3, false);
} else if (pdev->hdr_type == PCI_HEADER_TYPE_BRIDGE) {
- pci_restore_config_space_range(pdev, 12, 15, 0, false);
+ pci_restore_config_space_range(pdev, 12, 15, false);
/*
* Force rewriting of prefetch registers to avoid S3 resume
* issues on Intel PCI bridges that occur when these
* registers are not explicitly written.
*/
- pci_restore_config_space_range(pdev, 9, 11, 0, true);
- pci_restore_config_space_range(pdev, 0, 8, 0, false);
+ pci_restore_config_space_range(pdev, 9, 11, true);
+ pci_restore_config_space_range(pdev, 0, 8, false);
} else {
- pci_restore_config_space_range(pdev, 0, 15, 0, false);
+ pci_restore_config_space_range(pdev, 0, 15, false);
}
}
--
2.51.0
next reply other threads:[~2026-05-03 13:34 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-03 13:34 Lukas Wunner [this message]
2026-05-03 13:51 ` [PATCH] PCI: Drop unnecessary retries when restoring BARs sashiko-bot
2026-05-04 7:49 ` Lukas Wunner
2026-05-04 17:09 ` Bjorn Helgaas
2026-05-04 19:31 ` Rafael J. Wysocki
2026-05-04 21:17 ` Bjorn Helgaas
2026-05-05 10:43 ` Rafael J. Wysocki
2026-05-08 0:17 ` Bjorn Helgaas
2026-05-08 12:51 ` Rafael J. Wysocki
2026-05-08 21:43 ` Bjorn Helgaas
2026-05-11 15:24 ` Rafael J. Wysocki
2026-05-12 0:01 ` Bjorn Helgaas
2026-05-12 10:49 ` Rafael J. Wysocki
2026-05-22 22:31 ` Bjorn Helgaas
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