linux-kernel - [PATCH] p2sb: Don't init until unassigned resources have been assigned.

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Message-ID: <20240509164905.41016-1-bcfradella@proton.me>
Date: Thu, 09 May 2024 16:49:34 +0000
From: bcfradella@...ton.me
To: Hans de Goede <hdegoede@...hat.com>, Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>, platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: Ben Fradella <bfradell@...app.com>, Ranjan Dutta <ranjan.dutta@...el.com>, Yifan2 Li <yifan2.li@...el.com>, Jonathan Yong <jonathan.yong@...el.com>
Subject: [PATCH] p2sb: Don't init until unassigned resources have been assigned.

From: Ben Fradella <bfradell@...app.com>

The P2SB could get an invalid BAR from the BIOS, and that won't be fixed
up until pcibios_assign_resources(), which is an fs_initcall().

- Move p2sb_fs_init() to an fs_initcall_sync(). This is still early
  enough to avoid a race with any dependent drivers.

- Add a check for IORESOURCE_UNSET in p2sb_valid_resource() to catch
  unset BARs going forward.

- Return error values from p2sb_fs_init() so that the 'initcall_debug'
  cmdline arg provides useful data.

Signed-off-by: Ben Fradella <bfradell@...app.com>
---
 drivers/platform/x86/p2sb.c | 29 +++++++++++++++--------------
 1 file changed, 15 insertions(+), 14 deletions(-)

diff --git a/drivers/platform/x86/p2sb.c b/drivers/platform/x86/p2sb.c
index 3d66e1d4eb1f..1938a3ef9480 100644
--- a/drivers/platform/x86/p2sb.c
+++ b/drivers/platform/x86/p2sb.c
@@ -56,12 +56,9 @@ static int p2sb_get_devfn(unsigned int *devfn)
 	return 0;
 }
 
-static bool p2sb_valid_resource(struct resource *res)
+static bool p2sb_valid_resource(const struct resource *res)
 {
-	if (res->flags)
-		return true;
-
-	return false;
+	return res->flags & ~IORESOURCE_UNSET;
 }
 
 /* Copy resource from the first BAR of the device in question */
@@ -220,16 +217,20 @@ EXPORT_SYMBOL_GPL(p2sb_bar);
 
 static int __init p2sb_fs_init(void)
 {
-	p2sb_cache_resources();
-	return 0;
+	return p2sb_cache_resources();
 }
 
 /*
- * pci_rescan_remove_lock to avoid access to unhidden P2SB devices can
- * not be locked in sysfs pci bus rescan path because of deadlock. To
- * avoid the deadlock, access to P2SB devices with the lock at an early
- * step in kernel initialization and cache required resources. This
- * should happen after subsys_initcall which initializes PCI subsystem
- * and before device_initcall which requires P2SB resources.
+ * pci_rescan_remove_lock() can not be locked in sysfs pci bus rescan path
+ * because of deadlock. To avoid the deadlock, access P2SB devices with the lock
+ * at an early step in kernel initialization and cache required resources.
+ *
+ * We want to run as early as possible. If the P2SB was assigned a bad BAR,
+ * we'll need to wait on pcibios_assign_resources() to fix it. So, our list of
+ * initcall dependencies looks something like this:
+ *
+ * ...
+ * subsys_initcall (pci_subsys_init)
+ * fs_initcall     (pcibios_assign_resources)
  */
-fs_initcall(p2sb_fs_init);
+fs_initcall_sync(p2sb_fs_init);
-- 
2.43.0