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staging: android: persistent_ram: make persistent_ram_write atomic
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Allow persistent_ram_write to be called on multiple cpus at
the same time, as long as ecc is not in use.  Uses atomics
for the buffer->start and buffer->size counters.

[jstultz: Fix up some pr_info casting issues on 64bit]
CC: Greg KH <gregkh@linuxfoundation.org>
CC: Android Kernel Team <kernel-team@android.com>
Signed-off-by: Colin Cross <ccross@android.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Colin Cross authored and Greg Kroah-Hartman committed Mar 8, 2012
1 parent 404a604 commit 808d038
Showing 1 changed file with 101 additions and 39 deletions.
140 changes: 101 additions & 39 deletions drivers/staging/android/persistent_ram.c
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Original file line number Diff line number Diff line change
Expand Up @@ -27,15 +27,75 @@

struct persistent_ram_buffer {
uint32_t sig;
uint32_t start;
uint32_t size;
atomic_t start;
atomic_t size;
uint8_t data[0];
};

#define PERSISTENT_RAM_SIG (0x43474244) /* DBGC */

static __initdata LIST_HEAD(persistent_ram_list);

static inline size_t buffer_size(struct persistent_ram_zone *prz)
{
return atomic_read(&prz->buffer->size);
}

static inline size_t buffer_start(struct persistent_ram_zone *prz)
{
return atomic_read(&prz->buffer->start);
}

/* increase and wrap the start pointer, returning the old value */
static inline size_t buffer_start_add(struct persistent_ram_zone *prz, size_t a)
{
int old;
int new;

do {
old = atomic_read(&prz->buffer->start);
new = old + a;
while (unlikely(new > prz->buffer_size))
new -= prz->buffer_size;
} while (atomic_cmpxchg(&prz->buffer->start, old, new) != old);

return old;
}

/* increase the size counter until it hits the max size */
static inline void buffer_size_add(struct persistent_ram_zone *prz, size_t a)
{
size_t old;
size_t new;

if (atomic_read(&prz->buffer->size) == prz->buffer_size)
return;

do {
old = atomic_read(&prz->buffer->size);
new = old + a;
if (new > prz->buffer_size)
new = prz->buffer_size;
} while (atomic_cmpxchg(&prz->buffer->size, old, new) != old);
}

/* increase the size counter, retuning an error if it hits the max size */
static inline ssize_t buffer_size_add_clamp(struct persistent_ram_zone *prz,
size_t a)
{
size_t old;
size_t new;

do {
old = atomic_read(&prz->buffer->size);
new = old + a;
if (new > prz->buffer_size)
return -ENOMEM;
} while (atomic_cmpxchg(&prz->buffer->size, old, new) != old);

return 0;
}

static void persistent_ram_encode_rs8(struct persistent_ram_zone *prz,
uint8_t *data, size_t len, uint8_t *ecc)
{
Expand All @@ -62,7 +122,7 @@ static int persistent_ram_decode_rs8(struct persistent_ram_zone *prz,
}

static void persistent_ram_update_ecc(struct persistent_ram_zone *prz,
unsigned int count)
unsigned int start, unsigned int count)
{
struct persistent_ram_buffer *buffer = prz->buffer;
uint8_t *buffer_end = buffer->data + prz->buffer_size;
Expand All @@ -75,16 +135,16 @@ static void persistent_ram_update_ecc(struct persistent_ram_zone *prz,
if (!prz->ecc)
return;

block = buffer->data + (buffer->start & ~(ecc_block_size - 1));
par = prz->par_buffer +
(buffer->start / ecc_block_size) * prz->ecc_size;
block = buffer->data + (start & ~(ecc_block_size - 1));
par = prz->par_buffer + (start / ecc_block_size) * prz->ecc_size;

do {
if (block + ecc_block_size > buffer_end)
size = buffer_end - block;
persistent_ram_encode_rs8(prz, block, size, par);
block += ecc_block_size;
par += ecc_size;
} while (block < buffer->data + buffer->start + count);
} while (block < buffer->data + start + count);
}

static void persistent_ram_update_header_ecc(struct persistent_ram_zone *prz)
Expand All @@ -109,7 +169,7 @@ static void persistent_ram_ecc_old(struct persistent_ram_zone *prz)

block = buffer->data;
par = prz->par_buffer;
while (block < buffer->data + buffer->size) {
while (block < buffer->data + buffer_size(prz)) {
int numerr;
int size = prz->ecc_block_size;
if (block + size > buffer->data + prz->buffer_size)
Expand Down Expand Up @@ -199,60 +259,60 @@ ssize_t persistent_ram_ecc_string(struct persistent_ram_zone *prz,
}

static void persistent_ram_update(struct persistent_ram_zone *prz,
const void *s, unsigned int count)
const void *s, unsigned int start, unsigned int count)
{
struct persistent_ram_buffer *buffer = prz->buffer;
memcpy(buffer->data + buffer->start, s, count);
persistent_ram_update_ecc(prz, count);
memcpy(buffer->data + start, s, count);
persistent_ram_update_ecc(prz, start, count);
}

static void __init
persistent_ram_save_old(struct persistent_ram_zone *prz)
{
struct persistent_ram_buffer *buffer = prz->buffer;
size_t old_log_size = buffer->size;
size_t size = buffer_size(prz);
size_t start = buffer_start(prz);
char *dest;

persistent_ram_ecc_old(prz);

dest = kmalloc(old_log_size, GFP_KERNEL);
dest = kmalloc(size, GFP_KERNEL);
if (dest == NULL) {
pr_err("persistent_ram: failed to allocate buffer\n");
return;
}

prz->old_log = dest;
prz->old_log_size = old_log_size;
memcpy(prz->old_log,
&buffer->data[buffer->start], buffer->size - buffer->start);
memcpy(prz->old_log + buffer->size - buffer->start,
&buffer->data[0], buffer->start);
prz->old_log_size = size;
memcpy(prz->old_log, &buffer->data[start], size - start);
memcpy(prz->old_log + size - start, &buffer->data[0], start);
}

int persistent_ram_write(struct persistent_ram_zone *prz,
const void *s, unsigned int count)
{
int rem;
int c = count;
struct persistent_ram_buffer *buffer = prz->buffer;
size_t start;

if (c > prz->buffer_size) {
if (unlikely(c > prz->buffer_size)) {
s += c - prz->buffer_size;
c = prz->buffer_size;
}
rem = prz->buffer_size - buffer->start;
if (rem < c) {
persistent_ram_update(prz, s, rem);

buffer_size_add_clamp(prz, c);

start = buffer_start_add(prz, c);

rem = prz->buffer_size - start;
if (unlikely(rem < c)) {
persistent_ram_update(prz, s, start, rem);
s += rem;
c -= rem;
buffer->start = 0;
buffer->size = prz->buffer_size;
start = 0;
}
persistent_ram_update(prz, s, c);
persistent_ram_update(prz, s, start, c);

buffer->start += c;
if (buffer->size < prz->buffer_size)
buffer->size += c;
persistent_ram_update_header_ecc(prz);

return count;
Expand Down Expand Up @@ -361,23 +421,25 @@ struct persistent_ram_zone *__persistent_ram_init(struct device *dev, bool ecc)
return ERR_PTR(ret);

if (prz->buffer->sig == PERSISTENT_RAM_SIG) {
if (prz->buffer->size > prz->buffer_size
|| prz->buffer->start > prz->buffer->size)
pr_info("persistent_ram: found existing invalid buffer, size %d, start %d\n",
prz->buffer->size, prz->buffer->start);
if (buffer_size(prz) > prz->buffer_size ||
buffer_start(prz) > buffer_size(prz))
pr_info("persistent_ram: found existing invalid buffer,"
" size %ld, start %ld\n",
buffer_size(prz), buffer_start(prz));
else {
pr_info("persistent_ram: found existing buffer, size %d, start %d\n",
prz->buffer->size, prz->buffer->start);
pr_info("persistent_ram: found existing buffer,"
" size %ld, start %ld\n",
buffer_size(prz), buffer_start(prz));
persistent_ram_save_old(prz);
}
} else {
pr_info("persistent_ram: no valid data in buffer (sig = 0x%08x)\n",
prz->buffer->sig);
pr_info("persistent_ram: no valid data in buffer"
" (sig = 0x%08x)\n", prz->buffer->sig);
}

prz->buffer->sig = PERSISTENT_RAM_SIG;
prz->buffer->start = 0;
prz->buffer->size = 0;
atomic_set(&prz->buffer->start, 0);
atomic_set(&prz->buffer->size, 0);

return prz;
}
Expand Down

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