[RFC PATCH 1/2] pci: determine CLS more intelligently

[Tejun Heo]

Till now, CLS has been determined either by arch code or as
L1_CACHE_BYTES.  Only x86 and ia64 set CLS explicitly and x86 doesn't
always get it right.  On most configurations, the chance is that
firmware configures the correct value during boot.

This patch makes pci_init() determine CLS by looking at what firmware
has configured.  It scans all devices and if all non-zero values
agree, the value is used.  If none is configured or there is a
disagreement, pci_dfl_cache_line_size is used.  arch can set the dfl
value (via PCI_CACHE_LINE_BYTES or pci_dfl_cache_line_size) or
override the actual one.

ia64, x86 and sparc64 updated to set the default cls instead of the
actual one.  sparc64 is currently the only one using
PCI_CACHE_LINE_BYTES.  It would be nice to update it to set the
default variable instead.

RFC PATCH, PLEASE DON'T APPLY YET.
Cc: Greg KH <gregkh@xxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: David Miller <davem@xxxxxxxxxxxxx>
---
These two patches are refreshed version of the following patch.

 http://thread.gmane.org/gmane.linux.kernel.pci/4418/focus=4431

This patch improves how CLS is determined and was written mainly
because the original code didn't get it right on my laptop (lenovo
x61s, the determined value was 32 but the value bios used for other
devices was 64).  For x86, maybe we can remove the arch specific
configuration codes in the long run?

Seems to work fine on my test machine and laptop.  Also builds fine
for powerpc64 and sparc64.

Axel, to test, you'll need to build a vanialla kernel with the patches
applied.  There are pretty good docs about doing that on the web.

Thanks.

 arch/ia64/pci/pci.c   |    8 ++++----
 arch/x86/pci/common.c |    8 ++++----
 drivers/pci/pci.c     |   49 +++++++++++++++++++++++++++++++++++++++++--------
 3 files changed, 49 insertions(+), 16 deletions(-)

Index: work/arch/ia64/pci/pci.c
===================================================================
--- work.orig/arch/ia64/pci/pci.c
+++ work/arch/ia64/pci/pci.c
@@ -716,7 +716,7 @@ int ia64_pci_legacy_write(struct pci_bus
 }
 
 /* It's defined in drivers/pci/pci.c */
-extern u8 pci_cache_line_size;
+extern u8 pci_dfl_cache_line_size;
 
 /**
  * set_pci_cacheline_size - determine cacheline size for PCI devices
@@ -726,7 +726,7 @@ extern u8 pci_cache_line_size;
  *
  * Code mostly taken from arch/ia64/kernel/palinfo.c:cache_info().
  */
-static void __init set_pci_cacheline_size(void)
+static void __init set_pci_dfl_cacheline_size(void)
 {
 	unsigned long levels, unique_caches;
 	long status;
@@ -746,7 +746,7 @@ static void __init set_pci_cacheline_siz
 			"(status=%ld)\n", __func__, status);
 		return;
 	}
-	pci_cache_line_size = (1 << cci.pcci_line_size) / 4;
+	pci_dfl_cache_line_size = (1 << cci.pcci_line_size) / 4;
 }
 
 u64 ia64_dma_get_required_mask(struct device *dev)
@@ -777,7 +777,7 @@ EXPORT_SYMBOL_GPL(dma_get_required_mask)
 
 static int __init pcibios_init(void)
 {
-	set_pci_cacheline_size();
+	set_pci_dfl_cacheline_size();
 	return 0;
 }
 
Index: work/arch/x86/pci/common.c
===================================================================
--- work.orig/arch/x86/pci/common.c
+++ work/arch/x86/pci/common.c
@@ -410,7 +410,7 @@ struct pci_bus * __devinit pcibios_scan_
 	return bus;
 }
 
-extern u8 pci_cache_line_size;
+extern u8 pci_dfl_cache_line_size;
 
 int __init pcibios_init(void)
 {
@@ -426,11 +426,11 @@ int __init pcibios_init(void)
 	 * and P4. It's also good for 386/486s (which actually have 16)
 	 * as quite a few PCI devices do not support smaller values.
 	 */
-	pci_cache_line_size = 32 >> 2;
+	pci_dfl_cache_line_size = 32 >> 2;
 	if (c->x86 >= 6 && c->x86_vendor == X86_VENDOR_AMD)
-		pci_cache_line_size = 64 >> 2;	/* K7 & K8 */
+		pci_dfl_cache_line_size = 64 >> 2;	/* K7 & K8 */
 	else if (c->x86 > 6 && c->x86_vendor == X86_VENDOR_INTEL)
-		pci_cache_line_size = 128 >> 2;	/* P4 */
+		pci_dfl_cache_line_size = 128 >> 2;	/* P4 */
 
 	pcibios_resource_survey();
 
Index: work/drivers/pci/pci.c
===================================================================
--- work.orig/drivers/pci/pci.c
+++ work/drivers/pci/pci.c
@@ -41,6 +41,19 @@ int pci_domains_supported = 1;
 unsigned long pci_cardbus_io_size = DEFAULT_CARDBUS_IO_SIZE;
 unsigned long pci_cardbus_mem_size = DEFAULT_CARDBUS_MEM_SIZE;
 
+#ifndef PCI_CACHE_LINE_BYTES
+#define PCI_CACHE_LINE_BYTES L1_CACHE_BYTES
+#endif
+
+/*
+ * The default CLS is used if arch didn't set CLS explicitly and not
+ * all pci devices agree on the same value.  Arch can override either
+ * the dfl or actual value as it sees fit.  Don't forget this is
+ * measured in 32-bit words, not bytes.
+ */
+u8 pci_dfl_cache_line_size __initdata = PCI_CACHE_LINE_BYTES >> 2;
+u8 pci_cache_line_size;
+
 /**
  * pci_bus_max_busnr - returns maximum PCI bus number of given bus' children
  * @bus: pointer to PCI bus structure to search
@@ -1848,14 +1861,6 @@ void pci_clear_mwi(struct pci_dev *dev)
 
 #else
 
-#ifndef PCI_CACHE_LINE_BYTES
-#define PCI_CACHE_LINE_BYTES L1_CACHE_BYTES
-#endif
-
-/* This can be overridden by arch code. */
-/* Don't forget this is measured in 32-bit words, not bytes */
-u8 pci_cache_line_size = PCI_CACHE_LINE_BYTES / 4;
-
 /**
  * pci_set_cacheline_size - ensure the CACHE_LINE_SIZE register is programmed
  * @dev: the PCI device for which MWI is to be enabled
@@ -2631,9 +2636,37 @@ int __attribute__ ((weak)) pci_ext_cfg_a
 static int __devinit pci_init(void)
 {
 	struct pci_dev *dev = NULL;
+	u8 cls = 0;
+	u8 tmp;
+
+	if (pci_cache_line_size)
+		printk(KERN_DEBUG "PCI: CLS %u bytes\n",
+		       pci_cache_line_size << 2);
 
 	while ((dev = pci_get_device(PCI_ANY_ID, PCI_ANY_ID, dev)) != NULL) {
 		pci_fixup_device(pci_fixup_final, dev);
+		/*
+		 * If arch hasn't set it explicitly yet, use the CLS
+		 * value shared by all PCI devices.  If there's a
+		 * mismatch, fall back to the default value.
+		 */
+		if (!pci_cache_line_size) {
+			pci_read_config_byte(dev, PCI_CACHE_LINE_SIZE, &tmp);
+			if (!cls)
+				cls = tmp;
+			if (!tmp || cls == tmp)
+				continue;
+
+			printk(KERN_DEBUG "PCI: CLS mismatch (%u != %u), "
+			       "using %u bytes\n", cls << 2, tmp << 2,
+			       pci_dfl_cache_line_size << 2);
+			pci_cache_line_size = pci_dfl_cache_line_size;
+		}
+	}
+	if (!pci_cache_line_size) {
+		printk(KERN_DEBUG "PCI: CLS %u bytes, default %u\n",
+		       cls << 2, pci_dfl_cache_line_size << 2);
+		pci_cache_line_size = cls;
 	}
 
 	return 0;
--
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