redonkable/remarkable-linux
redonkable/remarkable-linux
1
0
Fork 0
Code Releases Activity

coresight: tmc: getting rid of multiple read access

Browse source 
Allowing multiple readers to access the trace data simultaniously
via sysFS provides no shortage of opportunity for race condition,
mandates two variable to be maintained (drvdata::read_count and
drvdata::reading), makes the code complex and provide little
advantages, if any.

This patch streamlines the read process by restricting trace data
access to a single user.  That way drvdata::read_count can
be eliminated and race conditions (along with faulty error handling)
in function tmc_open() and tmc_release() eliminated.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Mathieu Poirier 2016-05-03 11:33:53 -06:00 committed by Greg Kroah-Hartman
parent de5461970b
commit f74debbea0
4 changed files with 18 additions and 17 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

5
drivers/hwtracing/coresight/coresight-tmc-etf.c
View file

@ -260,6 +260,11 @@ int tmc_read_prepare_etb(struct tmc_drvdata *drvdata)
spin_lock_irqsave(&drvdata->spinlock, flags);
if (drvdata->reading) {
ret = -EBUSY;
goto out;
}
/* There is no point in reading a TMC in HW FIFO mode */
mode = readl_relaxed(drvdata->base + TMC_MODE);
if (mode != TMC_MODE_CIRCULAR_BUFFER) {

4
drivers/hwtracing/coresight/coresight-tmc-etr.c
View file

@ -188,6 +188,10 @@ int tmc_read_prepare_etr(struct tmc_drvdata *drvdata)
return -EINVAL;
spin_lock_irqsave(&drvdata->spinlock, flags);
if (drvdata->reading) {
ret = -EBUSY;
goto out;
}
/* If drvdata::buf is NULL the trace data has been read already */
if (drvdata->buf == NULL) {

24
drivers/hwtracing/coresight/coresight-tmc.c
View file

@ -95,7 +95,7 @@ static int tmc_read_prepare(struct tmc_drvdata *drvdata)
return ret;
}
static void tmc_read_unprepare(struct tmc_drvdata *drvdata)
static int tmc_read_unprepare(struct tmc_drvdata *drvdata)
{
int ret = 0;
@ -113,21 +113,20 @@ static void tmc_read_unprepare(struct tmc_drvdata *drvdata)
if (!ret)
dev_info(drvdata->dev, "TMC read end\n");
return ret;
}
static int tmc_open(struct inode *inode, struct file *file)
{
int ret;
struct tmc_drvdata *drvdata = container_of(file->private_data,
struct tmc_drvdata, miscdev);
int ret = 0;
if (drvdata->read_count++)
goto out;
ret = tmc_read_prepare(drvdata);
if (ret)
return ret;
out:
nonseekable_open(inode, file);
dev_dbg(drvdata->dev, "%s: successfully opened\n", __func__);
@ -167,19 +166,14 @@ static ssize_t tmc_read(struct file *file, char __user *data, size_t len,
static int tmc_release(struct inode *inode, struct file *file)
{
int ret;
struct tmc_drvdata *drvdata = container_of(file->private_data,
struct tmc_drvdata, miscdev);
if (--drvdata->read_count) {
if (drvdata->read_count < 0) {
dev_err(drvdata->dev, "mismatched close\n");
drvdata->read_count = 0;
}
goto out;
}
ret = tmc_read_unprepare(drvdata);
if (ret)
return ret;
tmc_read_unprepare(drvdata);
out:
dev_dbg(drvdata->dev, "%s: released\n", __func__);
return 0;
}

2
drivers/hwtracing/coresight/coresight-tmc.h
View file

@ -94,7 +94,6 @@ enum tmc_mem_intf_width {
* @csdev: component vitals needed by the framework.
* @miscdev: specifics to handle "/dev/xyz.tmc" entry.
* @spinlock: only one at a time pls.
* @read_count: manages preparation of buffer for reading.
* @buf: area of memory where trace data get sent.
* @paddr: DMA start location in RAM.
* @vaddr: virtual representation of @paddr.
@ -109,7 +108,6 @@ struct tmc_drvdata {
struct coresight_device *csdev;
struct miscdevice miscdev;
spinlock_t spinlock;
int read_count;
bool reading;
char *buf;
dma_addr_t paddr;