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Message-ID: <20140916205000.GA6672@atomide.com>
Date: Tue, 16 Sep 2014 13:50:01 -0700
From: Tony Lindgren <tony@...mide.com>
To: Russell King - ARM Linux <linux@....linux.org.uk>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org,
Arnd Bergmann <arnd@...db.de>,
Rob Herring <robherring2@...il.com>,
Randy Dunlap <rdunlap@...radead.org>,
Anton Vorontsov <anton@...msg.org>,
Colin Cross <ccross@...roid.com>,
Kees Cook <keescook@...omium.org>,
Olof Johansson <olof@...om.net>,
Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH 2/2] pstore-ram: Allow optional mapping with
pgprot_noncached
* Russell King - ARM Linux <linux@....linux.org.uk> [140912 16:16]:
> On Fri, Sep 12, 2014 at 11:32:25AM -0700, Tony Lindgren wrote:
> > On some ARMs at least the memory can be mapped pgprot_noncached()
> > and still be working for atomic operations. As pointed out by
> > Colin Cross <ccross@...roid.com>, in some cases you do want to use
> > pgprot_noncached() if the SoC supports it to see a debug printk
> > just before a write hanging the system.
> >
> > On ARMs, the atomic operations on strongly ordered memory are
> > implementation defined. So let's provide an optional kernel parameter
> > for configuring noncached memory, and use pgprot_writecombine() by
> > default.
>
> Can we clean up this terminology please?
>
> Writecombine memory is not cached - write combine memory bypasses the
> caches entirely. What it doesn't bypass are store buffers, which may
> combine two writes together. So, calling it "cached" is misleading.
Good point. I've pretty much s/cached/memtype/ and updated the
description too in the patch below.
> Secondly, memory returned by ioremap() is not strongly ordered, it is
> device memory. There's three main classifications of memory on ARM:
> strongly ordered, device and normal memory. Normal memory has attributes
> which define whether it is write combining, or cacheable in some way (and
> if so, how it's cacheable.)
>
> Exclusives are always permitted to normal memory. The other two are
> implementation defined. While an implementation may offer it on
> strongly ordered, that doesn't mean that it also supports it on device
> memory.
>
> Lastly, aliased mappings are something that ARM has always strongly
> discouraged on ARMv6+ (it was plain down-right unpredictable, but it's
> now "strongly discouraged") and remapping memory with different memory
> type should be avoided.
Yes thanks for the summary again. Maybe let's let this second patch float
on the lists for a while until we have somebody actually test it on
unbuffered memory.
Andrew, if no comments on 1/2 in this series, can you please pick it up
for fixes so we get pstore working?
Here's the updated version of the second patch for reference.
Regards,
Tony
8< -----------------
From: Tony Lindgren <tony@...mide.com>
Date: Thu, 11 Sep 2014 15:02:37 -0700
Subject: [PATCH] pstore-ram: Allow optional mapping with pgprot_noncached
On some ARMs the memory can be mapped pgprot_noncached() and still
be working for atomic operations. As pointed out by Colin Cross
<ccross@...roid.com>, in some cases you do want to use
pgprot_noncached() if the SoC supports it to see a debug printk
just before a write hanging the system.
On ARMs, the atomic operations on strongly ordered memory are
implementation defined. So let's provide an optional kernel parameter
for configuring pgprot_noncached(), and use pgprot_writecombine() by
default.
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Rob Herring <robherring2@...il.com>
Cc: Randy Dunlap <rdunlap@...radead.org>
Cc: Anton Vorontsov <anton@...msg.org>
Cc: Colin Cross <ccross@...roid.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Olof Johansson <olof@...om.net>
Cc: Tony Luck <tony.luck@...el.com>
Cc: Russell King <linux@....linux.org.uk>
Signed-off-by: Tony Lindgren <tony@...mide.com>
--- a/Documentation/ramoops.txt
+++ b/Documentation/ramoops.txt
@@ -14,11 +14,19 @@ survive after a restart.
1. Ramoops concepts
-Ramoops uses a predefined memory area to store the dump. The start and size of
-the memory area are set using two variables:
+Ramoops uses a predefined memory area to store the dump. The start and size
+and type of the memory area are set using three variables:
* "mem_address" for the start
* "mem_size" for the size. The memory size will be rounded down to a
power of two.
+ * "mem_type" to specifiy if the memory type (default is pgprot_writecombine).
+
+Typically the default value of mem_type=0 should be used as that sets the pstore
+mapping to pgprot_writecombine. Setting mem_type=1 attempts to use
+pgprot_noncached, which only works on some platforms. This is because pstore
+depends on atomic operations. At least on ARM, pgprot_noncached causes the
+memory to be mapped strongly ordered, and atomic operations on strongly ordered
+memory are implementation defined, and won't work on many ARMs such as omaps.
The memory area is divided into "record_size" chunks (also rounded down to
power of two) and each oops/panic writes a "record_size" chunk of
@@ -55,6 +63,7 @@ Setting the ramoops parameters can be done in 2 different manners:
static struct ramoops_platform_data ramoops_data = {
.mem_size = <...>,
.mem_address = <...>,
+ .mem_type = <...>,
.record_size = <...>,
.dump_oops = <...>,
.ecc = <...>,
--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -61,6 +61,11 @@ module_param(mem_size, ulong, 0400);
MODULE_PARM_DESC(mem_size,
"size of reserved RAM used to store oops/panic logs");
+static unsigned int mem_type;
+module_param(mem_type, uint, 0600);
+MODULE_PARM_DESC(mem_type,
+ "set to 1 to try to use unbuffered memory (default 0)");
+
static int dump_oops = 1;
module_param(dump_oops, int, 0600);
MODULE_PARM_DESC(dump_oops,
@@ -79,6 +84,7 @@ struct ramoops_context {
struct persistent_ram_zone *fprz;
phys_addr_t phys_addr;
unsigned long size;
+ unsigned int memtype;
size_t record_size;
size_t console_size;
size_t ftrace_size;
@@ -358,7 +364,8 @@ static int ramoops_init_przs(struct device *dev, struct ramoops_context *cxt,
size_t sz = cxt->record_size;
cxt->przs[i] = persistent_ram_new(*paddr, sz, 0,
- &cxt->ecc_info);
+ &cxt->ecc_info,
+ cxt->memtype);
if (IS_ERR(cxt->przs[i])) {
err = PTR_ERR(cxt->przs[i]);
dev_err(dev, "failed to request mem region (0x%zx@...llx): %d\n",
@@ -388,7 +395,7 @@ static int ramoops_init_prz(struct device *dev, struct ramoops_context *cxt,
return -ENOMEM;
}
- *prz = persistent_ram_new(*paddr, sz, sig, &cxt->ecc_info);
+ *prz = persistent_ram_new(*paddr, sz, sig, &cxt->ecc_info, cxt->memtype);
if (IS_ERR(*prz)) {
int err = PTR_ERR(*prz);
@@ -435,6 +442,7 @@ static int ramoops_probe(struct platform_device *pdev)
cxt->size = pdata->mem_size;
cxt->phys_addr = pdata->mem_address;
+ cxt->memtype = pdata->mem_type;
cxt->record_size = pdata->record_size;
cxt->console_size = pdata->console_size;
cxt->ftrace_size = pdata->ftrace_size;
@@ -564,6 +572,7 @@ static void ramoops_register_dummy(void)
dummy_data->mem_size = mem_size;
dummy_data->mem_address = mem_address;
+ dummy_data->mem_type = 0;
dummy_data->record_size = record_size;
dummy_data->console_size = ramoops_console_size;
dummy_data->ftrace_size = ramoops_ftrace_size;
--- a/fs/pstore/ram_core.c
+++ b/fs/pstore/ram_core.c
@@ -380,7 +380,8 @@ void persistent_ram_zap(struct persistent_ram_zone *prz)
persistent_ram_update_header_ecc(prz);
}
-static void *persistent_ram_vmap(phys_addr_t start, size_t size)
+static void *persistent_ram_vmap(phys_addr_t start, size_t size,
+ unsigned int memtype)
{
struct page **pages;
phys_addr_t page_start;
@@ -392,7 +393,10 @@ static void *persistent_ram_vmap(phys_addr_t start, size_t size)
page_start = start - offset_in_page(start);
page_count = DIV_ROUND_UP(size + offset_in_page(start), PAGE_SIZE);
- prot = pgprot_writecombine(PAGE_KERNEL);
+ if (memtype)
+ prot = pgprot_noncached(PAGE_KERNEL);
+ else
+ prot = pgprot_writecombine(PAGE_KERNEL);
pages = kmalloc_array(page_count, sizeof(struct page *), GFP_KERNEL);
if (!pages) {
@@ -411,8 +415,11 @@ static void *persistent_ram_vmap(phys_addr_t start, size_t size)
return vaddr;
}
-static void *persistent_ram_iomap(phys_addr_t start, size_t size)
+static void *persistent_ram_iomap(phys_addr_t start, size_t size,
+ unsigned int memtype)
{
+ void *va;
+
if (!request_mem_region(start, size, "persistent_ram")) {
pr_err("request mem region (0x%llx@...llx) failed\n",
(unsigned long long)size, (unsigned long long)start);
@@ -422,19 +429,24 @@ static void *persistent_ram_iomap(phys_addr_t start, size_t size)
buffer_start_add = buffer_start_add_locked;
buffer_size_add = buffer_size_add_locked;
- return ioremap_wc(start, size);
+ if (memtype)
+ va = ioremap(start, size);
+ else
+ va = ioremap_wc(start, size);
+
+ return va;
}
static int persistent_ram_buffer_map(phys_addr_t start, phys_addr_t size,
- struct persistent_ram_zone *prz)
+ struct persistent_ram_zone *prz, int memtype)
{
prz->paddr = start;
prz->size = size;
if (pfn_valid(start >> PAGE_SHIFT))
- prz->vaddr = persistent_ram_vmap(start, size);
+ prz->vaddr = persistent_ram_vmap(start, size, memtype);
else
- prz->vaddr = persistent_ram_iomap(start, size);
+ prz->vaddr = persistent_ram_iomap(start, size, memtype);
if (!prz->vaddr) {
pr_err("%s: Failed to map 0x%llx pages at 0x%llx\n", __func__,
@@ -500,7 +512,8 @@ void persistent_ram_free(struct persistent_ram_zone *prz)
}
struct persistent_ram_zone *persistent_ram_new(phys_addr_t start, size_t size,
- u32 sig, struct persistent_ram_ecc_info *ecc_info)
+ u32 sig, struct persistent_ram_ecc_info *ecc_info,
+ unsigned int memtype)
{
struct persistent_ram_zone *prz;
int ret = -ENOMEM;
@@ -511,7 +524,7 @@ struct persistent_ram_zone *persistent_ram_new(phys_addr_t start, size_t size,
goto err;
}
- ret = persistent_ram_buffer_map(start, size, prz);
+ ret = persistent_ram_buffer_map(start, size, prz, memtype);
if (ret)
goto err;
--- a/include/linux/pstore_ram.h
+++ b/include/linux/pstore_ram.h
@@ -53,7 +53,8 @@ struct persistent_ram_zone {
};
struct persistent_ram_zone *persistent_ram_new(phys_addr_t start, size_t size,
- u32 sig, struct persistent_ram_ecc_info *ecc_info);
+ u32 sig, struct persistent_ram_ecc_info *ecc_info,
+ unsigned int memtype);
void persistent_ram_free(struct persistent_ram_zone *prz);
void persistent_ram_zap(struct persistent_ram_zone *prz);
@@ -76,6 +77,7 @@ ssize_t persistent_ram_ecc_string(struct persistent_ram_zone *prz,
struct ramoops_platform_data {
unsigned long mem_size;
unsigned long mem_address;
+ unsigned int mem_type;
unsigned long record_size;
unsigned long console_size;
unsigned long ftrace_size;
--
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