linux-kernel - [PATCH 1/2] PCI: Relaxed tail alignment should never increase min

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Message-Id: <20250610102101.6496-2-ilpo.jarvinen@linux.intel.com>
Date: Tue, 10 Jun 2025 13:21:00 +0300
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Bjorn Helgaas <bhelgaas@...gle.com>,
	linux-pci@...r.kernel.org,
	Tudor Ambarus <tudor.ambarus@...aro.org>,
	Rio <rio@....me>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Cc: stable@...r.kernel.org
Subject: [PATCH 1/2] PCI: Relaxed tail alignment should never increase min_align

When using relaxed tail alignment for the bridge window,
pbus_size_mem() also tries to minimize min_align, which can under
certain scenarios end up increasing min_align from that found by
calculate_mem_align().

Ensure min_align is not increased by the relaxed tail alignment.

Eventually, it would be better to add calculate_relaxed_head_align()
similar to calculate_mem_align() which finds out what alignment can be
used for the head without introducing any gaps into the bridge window
to give flexibility on head address too. But that looks relatively
complex algorithm so it requires much more testing than fixing the
immediate problem causing a regression.

Fixes: 67f9085596ee ("PCI: Allow relaxed bridge window tail sizing for optional resources")
Reported-by: Rio <rio@....me>
Tested-by: Rio <rio@....me>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: <stable@...r.kernel.org>
---
 drivers/pci/setup-bus.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index 07c3d021a47e..f90d49cd07da 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -1169,6 +1169,7 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask,
 	resource_size_t children_add_size = 0;
 	resource_size_t children_add_align = 0;
 	resource_size_t add_align = 0;
+	resource_size_t relaxed_align;
 
 	if (!b_res)
 		return -ENOSPC;
@@ -1246,8 +1247,9 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask,
 	if (bus->self && size0 &&
 	    !pbus_upstream_space_available(bus, mask | IORESOURCE_PREFETCH, type,
 					   size0, min_align)) {
-		min_align = 1ULL << (max_order + __ffs(SZ_1M));
-		min_align = max(min_align, win_align);
+		relaxed_align = 1ULL << (max_order + __ffs(SZ_1M));
+		relaxed_align = max(relaxed_align, win_align);
+		min_align = min(min_align, relaxed_align);
 		size0 = calculate_memsize(size, min_size, 0, 0, resource_size(b_res), win_align);
 		pci_info(bus->self, "bridge window %pR to %pR requires relaxed alignment rules\n",
 			 b_res, &bus->busn_res);
@@ -1261,8 +1263,9 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask,
 		if (bus->self && size1 &&
 		    !pbus_upstream_space_available(bus, mask | IORESOURCE_PREFETCH, type,
 						   size1, add_align)) {
-			min_align = 1ULL << (max_order + __ffs(SZ_1M));
-			min_align = max(min_align, win_align);
+			relaxed_align = 1ULL << (max_order + __ffs(SZ_1M));
+			relaxed_align = max(min_align, win_align);
+			min_align = min(min_align, relaxed_align);
 			size1 = calculate_memsize(size, min_size, add_size, children_add_size,
 						  resource_size(b_res), win_align);
 			pci_info(bus->self,
-- 
2.39.5