[PATCH RFC 7/7] mmc: core: Add a debugfs entry to set max clock rate

Sayali Lokhande
2018-07-13T09:54:27Z

Limiting the max frequency supported by host controller
to a certain value can be useful for testing power consumption
at various frequencies that are supported by the host.
Note: If the card supports less than desired value then the
frequency of operation would be limited to that frequency.
Usage:
mount -t debugfs none /sys/kernel/debug
echo <desired_frequency> > /sys/kernel/debug/mmcX/max_clock
cat /sys/kernel/debug/mmcX/max_clock

Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>
Signed-off-by: Sayali Lokhande <sayalil@codeaurora.org>
---
drivers/mmc/core/debugfs.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 44 insertions(+)

diff --git a/drivers/mmc/core/debugfs.c b/drivers/mmc/core/debugfs.c
index 630ca8e..26499f7 100644
--- a/drivers/mmc/core/debugfs.c
+++ b/drivers/mmc/core/debugfs.c
@@ -262,6 +262,46 @@ static int mmc_scale_set(void *data, u64 val)
DEFINE_SIMPLE_ATTRIBUTE(mmc_scale_fops, mmc_scale_get, mmc_scale_set,
"%llu\n");

+static int mmc_max_clock_get(void *data, u64 *val)
+{
+ struct mmc_host *host = data;
+
+ if (!host)
+ return -EINVAL;
+
+ *val = host->f_max;
+
+ return 0;
+}
+
+static int mmc_max_clock_set(void *data, u64 val)
+{
+ struct mmc_host *host = data;
+ int err = -EINVAL;
+ unsigned long freq = val;
+ unsigned int old_freq;
+
+ if (!host || (val < host->f_min))
+ goto out;
+
+ mmc_claim_host(host);
+ if (host->bus_ops && host->bus_ops->change_bus_speed) {
+ old_freq = host->f_max;
+ host->f_max = freq;
+
+ err = host->bus_ops->change_bus_speed(host, &freq);
+
+ if (err)
+ host->f_max = old_freq;
+ }
+ mmc_release_host(host);
+out:
+ return err;
+}
+
+DEFINE_SIMPLE_ATTRIBUTE(mmc_max_clock_fops, mmc_max_clock_get,
+ mmc_max_clock_set, "%llu\n");
+
void mmc_add_host_debugfs(struct mmc_host *host)
{
struct dentry *root;
@@ -290,6 +330,10 @@ void mmc_add_host_debugfs(struct mmc_host *host)
&mmc_clock_fops))
goto err_node;

+ if (!debugfs_create_file("max_clock", 0600, root, host,
+ &mmc_max_clock_fops))
+ goto err_node;
+
if (!debugfs_create_file("scale", 0600, root, host,
&mmc_scale_fops))
goto err_node;