linux-kernel - Re: Cleaning up e820

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Message-ID: <1448907065.25710.0.camel@intel.com>
Date:	Mon, 30 Nov 2015 18:11:12 +0000
From:	"Williams, Dan J" <dan.j.williams@...el.com>
To:	"hch@...radead.org" <hch@...radead.org>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	"luto@...capital.net" <luto@...capital.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>
Subject: Re: Cleaning up e820_pmem?

On Sun, 2015-11-29 at 22:26 -0800, Andy Lutomirski wrote:
> My laptop has /sys/devices/platform/e820_pmem and autoloads all the
> nvdimm infrastructure.  While it would be really cool if my laptop
> had
> pmem, that's a bit of a pipe dream right now.  (Even if it did have
> it, this laptop is brand new -- it should use NFIT, not e820_pmem.)
> 
> Could we move the iomem_resource loop from drivers/nvdimm/e820.c to
> arch/x86/kernel/pmem.c and actually list the iomem resources the
> standard way as resources belonging to the platform device?  That
> would match accepted practice, and it would keep the grossly
> x86-specific part of the driver in arch/x86.  Then we could further
> tweak it to skip creating the platform device at all if there are no
> resources, and we'd avoid needlessly loading the module.
> 
> I'd do this myself, except that my lovely machine that *does* support
> e820 pmem has been repurposed, so testing on a machine that actually
> supports this turd is awkward for me.

This works for me...

8<---
Subject: libnvdimm, e820: skip module loading when no type-12

From: Dan Williams <dan.j.williams@...el.com>

If there are no persistent memory ranges present then don't bother
creating the platform device.  Otherwise, it loads the full libnvdimm
sub-system only to discover no resources present.

Reported-by: Andy Lutomirski <luto@...capital.net>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
 arch/x86/kernel/pmem.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/x86/kernel/pmem.c b/arch/x86/kernel/pmem.c
index 4f00b63d7ff3..14415aff1813 100644
--- a/arch/x86/kernel/pmem.c
+++ b/arch/x86/kernel/pmem.c
@@ -4,10 +4,22 @@
  */
 #include <linux/platform_device.h>
 #include <linux/module.h>
+#include <linux/ioport.h>
+
+static int found(u64 start, u64 end, void *data)
+{
+	return 1;
+}
 
 static __init int register_e820_pmem(void)
 {
+	char *pmem = "Persistent Memory (legacy)";
 	struct platform_device *pdev;
+	int rc;
+
+	rc = walk_iomem_res(pmem, IORESOURCE_MEM, 0, -1, NULL, found);
+	if (rc <= 0)
+		return 0;
 
 	/*
 	 * See drivers/nvdimm/e820.c for the implementation, this is--
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