linux-kernel - [PATCH 2/2] lguest: read offset of device

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Date:	Thu,  3 Mar 2016 13:01:41 +0100
From:	Paul Bolle <pebolle@...cali.nl>
To:	Rusty Russell <rusty@...tcorp.com.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
Cc:	x86@...nel.org, lguest@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] lguest: read offset of device_cap later

Read the offset of the capability with type VIRTIO_PCI_CAP_DEVICE_CFG
only when we're sure we're going to need it. Which is when all checks
have passed and we know we have a virtio console with an emerg_wr field.

Signed-off-by: Paul Bolle <pebolle@...cali.nl>
---
 arch/x86/lguest/boot.c | 12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c
index 535e3197d0c7..3b0c0eb4abf8 100644
--- a/arch/x86/lguest/boot.c
+++ b/arch/x86/lguest/boot.c
@@ -1233,8 +1233,6 @@ static void write_bar_via_cfg(u32 cfg_offset, u32 off, u32 val)
 static void probe_pci_console(void)
 {
 	u8 cap, common_cap = 0, device_cap = 0;
-	/* Offset within BAR0 */
-	u32 device_offset;
 	u32 device_len;
 
 	/* Avoid recursive printk into here. */
@@ -1258,21 +1256,16 @@ static void probe_pci_console(void)
 		u8 vndr = read_pci_config_byte(0, 1, 0, cap);
 		if (vndr == PCI_CAP_ID_VNDR) {
 			u8 type, bar;
-			u32 offset;
 
 			type = read_pci_config_byte(0, 1, 0,
 			    cap + offsetof(struct virtio_pci_cap, cfg_type));
 			bar = read_pci_config_byte(0, 1, 0,
 			    cap + offsetof(struct virtio_pci_cap, bar));
-			offset = read_pci_config(0, 1, 0,
-			    cap + offsetof(struct virtio_pci_cap, offset));
 
 			switch (type) {
 			case VIRTIO_PCI_CAP_DEVICE_CFG:
-				if (bar == 0) {
+				if (bar == 0)
 					device_cap = cap;
-					device_offset = offset;
-				}
 				break;
 			case VIRTIO_PCI_CAP_PCI_CFG:
 				console_access_cap = cap;
@@ -1302,7 +1295,8 @@ static void probe_pci_console(void)
 		return;
 	}
 
-	console_cfg_offset = device_offset;
+	console_cfg_offset = read_pci_config(0, 1, 0,
+			device_cap + offsetof(struct virtio_pci_cap, offset));
 	printk(KERN_INFO "lguest: Console via virtio-pci emerg_wr\n");
 }
 
-- 
2.4.3