Re: [PATCH 2/2] hwmon (pmbus): cffps: Add debugfs entries

[Guenter Roeck <linux@roeck-us.net>]

On Thu, Dec 07, 2017 at 04:19:45PM -0600, Eddie James wrote:
> 
> 
> On 12/07/2017 02:53 PM, Guenter Roeck wrote:
> >On Thu, Dec 07, 2017 at 01:50:38PM -0600, Eddie James wrote:
> >>From: "Edward A. James" <eajames@us.ibm.com>
> >>
> >>Add debugfs entries for additional power supply data, including part
> >>number, serial number, FRU number, firmware revision, ccin, and the
> >>input history of the power supply. The input history is 10 minutes of
> >>input power data in the form of twenty 30-second packets. Each packet
> >>contains average and maximum power for that 30 second period.
> >>
> >>Signed-off-by: Edward A. James <eajames@us.ibm.com>
> >>---
> >>  drivers/hwmon/pmbus/ibm-cffps.c | 199 +++++++++++++++++++++++++++++++++++++++-
> >>  1 file changed, 198 insertions(+), 1 deletion(-)
> >>
> >>diff --git a/drivers/hwmon/pmbus/ibm-cffps.c b/drivers/hwmon/pmbus/ibm-cffps.c
> >>index cb56da6..6d19399 100644
> >>--- a/drivers/hwmon/pmbus/ibm-cffps.c
> >>+++ b/drivers/hwmon/pmbus/ibm-cffps.c
> >>@@ -8,12 +8,26 @@
> >>   */
> >>  #include <linux/bitops.h>
> >>+#include <linux/debugfs.h>
> >>  #include <linux/device.h>
> >>+#include <linux/fs.h>
> >>  #include <linux/i2c.h>
> >>+#include <linux/jiffies.h>
> >>  #include <linux/module.h>
> >>+#include <linux/mutex.h>
> >>  #include "pmbus.h"
> >>+#define CFFPS_FRU_CMD				0x9A
> >>+#define CFFPS_PN_CMD				0x9B
> >>+#define CFFPS_SN_CMD				0x9E
> >>+#define CFFPS_CCIN_CMD				0xBD
> >>+#define CFFPS_FW_CMD_START			0xFA
> >>+#define CFFPS_FW_NUM_BYTES			4
> >>+
> >>+#define CFFPS_INPUT_HISTORY_CMD			0xD6
> >>+#define CFFPS_INPUT_HISTORY_SIZE		100
> >>+
> >>  /* STATUS_MFR_SPECIFIC bits */
> >>  #define CFFPS_MFR_FAN_FAULT			BIT(0)
> >>  #define CFFPS_MFR_THERMAL_FAULT			BIT(1)
> >>@@ -24,6 +38,144 @@
> >>  #define CFFPS_MFR_VAUX_FAULT			BIT(6)
> >>  #define CFFPS_MFR_CURRENT_SHARE_WARNING		BIT(7)
> >>+enum {
> >>+	CFFPS_DEBUGFS_INPUT_HISTORY = 0,
> >>+	CFFPS_DEBUGFS_FRU,
> >>+	CFFPS_DEBUGFS_PN,
> >>+	CFFPS_DEBUGFS_SN,
> >>+	CFFPS_DEBUGFS_CCIN,
> >>+	CFFPS_DEBUGFS_FW,
> >>+	CFFPS_DEBUGFS_NUM_ENTRIES
> >>+};
> >>+
> >>+struct ibm_cffps_input_history {
> >>+	struct mutex update_lock;
> >>+	unsigned long last_update;
> >>+
> >>+	u8 byte_count;
> >>+	u8 data[CFFPS_INPUT_HISTORY_SIZE];
> >>+};
> >>+
> >>+struct ibm_cffps {
> >>+	struct i2c_client *client;
> >>+
> >>+	struct ibm_cffps_input_history input_history;
> >>+
> >>+	int debugfs_entries[CFFPS_DEBUGFS_NUM_ENTRIES];
> >>+};
> >>+
> >>+#define to_psu(x, y) container_of((x), struct ibm_cffps, debugfs_entries[(y)])
> >>+
> >>+static ssize_t ibm_cffps_read_input_history(struct ibm_cffps *psu,
> >>+					    char __user *buf, size_t count,
> >>+					    loff_t *ppos)
> >>+{
> >>+	int rc;
> >>+	u8 msgbuf0[1] = { CFFPS_INPUT_HISTORY_CMD };
> >>+	u8 msgbuf1[CFFPS_INPUT_HISTORY_SIZE + 1] = { 0 };
> >>+	struct i2c_msg msg[2] = {
> >>+		{
> >>+			.addr = psu->client->addr,
> >>+			.flags = psu->client->flags,
> >>+			.len = 1,
> >>+			.buf = msgbuf0,
> >>+		}, {
> >>+			.addr = psu->client->addr,
> >>+			.flags = psu->client->flags | I2C_M_RD,
> >>+			.len = CFFPS_INPUT_HISTORY_SIZE + 1,
> >>+			.buf = msgbuf1,
> >>+		},
> >>+	};
> >>+
> >>+	if (!*ppos) {
> >>+		mutex_lock(&psu->input_history.update_lock);
> >>+		if (time_after(jiffies, psu->input_history.last_update + HZ)) {
> >>+			/*
> >>+			 * Use a raw i2c transfer, since we need more bytes
> >>+			 * than Linux I2C supports through smbus xfr (only 32).
> >>+			 */
> >>+			rc = i2c_transfer(psu->client->adapter, msg, 2);
> >>+			if (rc < 0) {
> >>+				mutex_unlock(&psu->input_history.update_lock);
> >>+				return rc;
> >>+			}
> >>+
> >>+			psu->input_history.byte_count = msgbuf1[0];
> >>+			memcpy(psu->input_history.data, &msgbuf1[1],
> >>+			       CFFPS_INPUT_HISTORY_SIZE);
> >>+			psu->input_history.last_update = jiffies;
> >>+		}
> >>+
> >>+		mutex_unlock(&psu->input_history.update_lock);
> >>+	}
> >>+
> >>+	return simple_read_from_buffer(buf, count, ppos,
> >>+				       psu->input_history.data,
> >>+				       psu->input_history.byte_count);
> >>+}
> >>+
> >>+static ssize_t ibm_cffps_debugfs_op(struct file *file, char __user *buf,
> >>+				    size_t count, loff_t *ppos)
> >>+{
> >>+	u8 cmd;
> >>+	int i, rc;
> >>+	int *idxp = file->private_data;
> >>+	int idx = *idxp;
> >>+	struct ibm_cffps *psu = to_psu(idxp, idx);
> >>+	char data[I2C_SMBUS_BLOCK_MAX] = { 0 };
> >>+
> >>+	switch (idx) {
> >>+	case CFFPS_DEBUGFS_INPUT_HISTORY:
> >>+		return ibm_cffps_read_input_history(psu, buf, count, ppos);
> >>+	case CFFPS_DEBUGFS_FRU:
> >>+		cmd = CFFPS_FRU_CMD;
> >>+		break;
> >>+	case CFFPS_DEBUGFS_PN:
> >>+		cmd = CFFPS_PN_CMD;
> >>+		break;
> >>+	case CFFPS_DEBUGFS_SN:
> >>+		cmd = CFFPS_SN_CMD;
> >>+		break;
> >>+	case CFFPS_DEBUGFS_CCIN:
> >>+		rc = i2c_smbus_read_word_data(psu->client, CFFPS_CCIN_CMD);
> >>+		if (rc < 0)
> >>+			return rc;
> >>+
> >>+		rc = snprintf(data, 5, "%04X", rc);
> >>+		goto done;
> >>+	case CFFPS_DEBUGFS_FW:
> >>+		for (i = 0; i < CFFPS_FW_NUM_BYTES; ++i) {
> >>+			rc = i2c_smbus_read_byte_data(psu->client,
> >>+						      CFFPS_FW_CMD_START + i);
> >>+			if (rc < 0)
> >>+				return rc;
> >>+
> >>+			snprintf(&data[i * 2], 3, "%02X", rc);
> >>+		}
> >>+
> >>+		rc = i * 2;
> >>+		goto done;
> >>+	default:
> >>+		return -EINVAL;
> >>+	}
> >>+
> >>+	rc = i2c_smbus_read_block_data(psu->client, cmd, data);
> >>+	if (rc < 0)
> >>+		return rc;
> >>+
> >>+done:
> >>+	data[rc] = '\n';
> >>+	rc += 2;
> >>+
> >>+	return simple_read_from_buffer(buf, count, ppos, data, rc);
> >>+}
> >>+
> >>+static const struct file_operations ibm_cffps_fops = {
> >>+	.llseek = noop_llseek,
> >>+	.read = ibm_cffps_debugfs_op,
> >>+	.open = simple_open,
> >>+};
> >>+
> >>  static int ibm_cffps_read_byte_data(struct i2c_client *client, int page,
> >>  				    int reg)
> >>  {
> >>@@ -119,7 +271,52 @@ static int ibm_cffps_read_word_data(struct i2c_client *client, int page,
> >>  static int ibm_cffps_probe(struct i2c_client *client,
> >>  			   const struct i2c_device_id *id)
> >>  {
> >>-	return pmbus_do_probe(client, id, &ibm_cffps_info);
> >>+	int i, rc;
> >>+	struct dentry *debugfs;
> >>+	struct ibm_cffps *psu;
> >>+
> >>+	rc = pmbus_do_probe(client, id, &ibm_cffps_info);
> >>+	if (rc)
> >>+		return rc;
> >>+
> >>+	/* Don't fail the probe if we can't create debugfs */
> >>+	psu = devm_kzalloc(&client->dev, sizeof(*psu), GFP_KERNEL);
> >>+	if (!psu)
> >>+		return 0;
> >>+
> >>+	psu->client = client;
> >>+	mutex_init(&psu->input_history.update_lock);
> >>+	if (jiffies > HZ)
> >>+		/* time_after wouldn't succeed with last_update = 0 in test */
> >... but you are setting it to 'jiffies' elsewhere, so it can still end up
> >being 0 at some point, especially since 'jiffies' starts with a large number
> >and wraps a few minutes after boot. Not sure I understand the problem,
> >actually.  Can you elaborate ?
> 
> Yea, not sure I understand it either, but basically, if we don't set
> last_update to jiffies - HZ or similar at start up, the check above for
> time_after(jiffies, last_upate + HZ) doesn't succeed soon after the boot.
> This doesn't make any sense to me, unless time_after is broken, but setting
> last_update to something relative to jiffies during probe fixes it.
> 
That is easy; just set it unconditionally to jiffies - HZ.
The 'jiffies > HZ' check is wrong; if jiffies happens to be < HZ,
you'd still want to set the value to jiffies - HZ (and it will be
somewhere between ULONG_MAX-HZ+1 .. ULONG_MAX).

Problem is that jiffies doesn't start with 0 but with something large.
That is why drivers typically have a 'valid' flag in addition to
the jiffies check.

Thanks,
Guenter