[PATCH] usb: early: xhci-dbc: Ensure correct memory size for early_ioremap()

[Umang Jain <uajain@igalia.com>]

early_ioremap() checks and fail, if the memory size exceeds the fixed
boot-time mappings (dictated by NR_FIX_BTMAPS macro). We should ensure
the correct maximum memory size is passed to early_ioremap() in the
driver.

Without this check and page size being 4K(4096), enabling xhci-dbc
on steamdeck seems to issue the warning:

steamdeck kernel: xhci_dbc:early_xdbc_parse_parameter: dbgp_num: 0
steamdeck kernel: ------------[ cut here ]------------
ay 19 13:42:57 steamdeck kernel: WARNING: CPU: 0 PID: 0 at mm/early_ioremap.c:139 __early_ioremap+0xae/0x180
steamdeck kernel: Modules linked in:
steamdeck kernel: CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.18.25-valve1-gcab630e7af50 #13 PREEMPT(undef)  4b70872d9de6788b7f2d10dce46ada89e6cd177b
steamdeck kernel: RIP: 0010:__early_ioremap+0xae/0x180
steamdeck kernel: Code: 60 ba 3f a0 4c 89 ca 48 81 e3 00 f0 ff ff 48 81 e2 00 f0 ff ff 48 29 d3 48 89 14 24 48 89 da 48 c1 ea 0c 89 d5 83 fa 40 76 04 <0f> 0b eb a2 6b c0 c0 4d 89 ce 41 81 e6 ff 0f 00 00 44 8d b8 ff 05
steamdeck kernel: RSP: 0000:ffffffff9fa03cb8 EFLAGS: 00010006 ORIG_RAX: 0000000000000000
steamdeck kernel: RAX: 0000000000000000 RBX: 0000000000100000 RCX: 0000000000100000
steamdeck kernel: RDX: 0000000000000100 RSI: 0000000000100000 RDI: 0000000080200000
steamdeck kernel: RBP: 0000000000000100 R08: 0000000000000000 R09: 0000000080200000
steamdeck kernel: R10: 0000000000000004 R11: ffffffff9fa03ad0 R12: 8000000000000163
steamdeck kernel: R13: 0000000000000000 R14: 0000000080200000 R15: 0000000000000000
steamdeck kernel: FS:  0000000000000000(0000) GS:0000000000000000(0000) knlGS:0000000000000000
steamdeck kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
steamdeck kernel: CR2: ffff888000000413 CR3: 000000020ed02000 CR4: 00000000000000b0
steamdeck kernel: Call Trace:
steamdeck kernel:  <TASK>
steamdeck kernel:  ? early_xdbc_parse_parameter+0x32c/0x360
steamdeck kernel:  ? setup_early_printk+0x4f5/0x520
steamdeck kernel:  ? do_early_param+0x44/0x70
steamdeck kernel:  ? parse_args+0x233/0x420
steamdeck kernel:  ? __pfx_do_early_param+0x10/0x10
steamdeck kernel:  ? parse_early_options+0x29/0x30
steamdeck kernel:  ? __pfx_do_early_param+0x10/0x10
steamdeck kernel:  ? parse_early_param+0x64/0xc0
steamdeck kernel:  ? setup_arch+0x542/0xbc0
steamdeck kernel:  ? _printk+0x6b/0x90
steamdeck kernel:  ? start_kernel+0x66/0x9a0
steamdeck kernel:  ? x86_64_start_reservations+0x24/0x30
steamdeck kernel:  ? x86_64_start_kernel+0xcc/0xd0
steamdeck kernel:  ? common_startup_64+0x13e/0x141
steamdeck kernel:  </TASK>
steamdeck kernel: ---[ end trace 0000000000000000 ]---

Signed-off-by: Umang Jain <uajain@igalia.com>
---
 drivers/usb/early/xhci-dbc.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/usb/early/xhci-dbc.c b/drivers/usb/early/xhci-dbc.c
index 41118bba9197..699a9ac6d6c3 100644
--- a/drivers/usb/early/xhci-dbc.c
+++ b/drivers/usb/early/xhci-dbc.c
@@ -76,6 +76,14 @@ static void __iomem * __init xdbc_map_pci_mmio(u32 bus, u32 dev, u32 func)
 
 	sz64 = 1ULL << __ffs64(sz64);
 
+	/*
+	 * Check that size does not exceed fixed boot-time mappings
+	 * dictated by NR_FIX_BTMAPS. early_ioremap() will WARN_ON()
+	 * and not map memory in those cases.
+	 */
+	if (sz64 > (NR_FIX_BTMAPS << PAGE_SHIFT))
+		sz64 = NR_FIX_BTMAPS << PAGE_SHIFT;
+
 	/* Check if the mem space is enabled: */
 	byte = read_pci_config_byte(bus, dev, func, PCI_COMMAND);
 	if (!(byte & PCI_COMMAND_MEMORY)) {
-- 
2.53.0