Debug with sysfs or debugfs nodes

To identify the status or update the state, use the sysfs and debugfs nodes. Mount debugfs to ensure that the debugfs file system is accessible for the debug nodes.

mount -t debugfs none /sys/kernel/debug

UFS device state commands

Required UFS device state information	Command
Check PA/DL error count	`cat /sys/kernel/debug/ufshcd/1d84000.ufshc/stats`
Read UFS device gating delay, in ms	`cat /sys/devices/platform/soc@0/1d84000.ufshc/clkgate_delay_ms`
Read UFS device clocks current frequency at given point	`cat /sys/devices/platform/soc@0/1d84000.ufshc/devfreq/1d84000.ufshc/cur_freq`
Read UFS device I/O scheduler details	`cat /sys/devices/platform/soc@0/1d84000.ufshc/devfreq/1d84000.ufshc/governor`
Read UFS device min frequency during clock scale down	`cat /sys/devices/platform/soc@0/1d84000.ufshc/devfreq/1d84000.ufshc/min_freq`
Read UFS device max frequency during clock scale up	`cat /sys/devices/platform/soc@0/1d84000.ufshc/devfreq/1d84000.ufshc/max_freq`
Read UFS device state active or sleep	`cat /sys/devices/platform/soc@0/1d84000.ufshc/power_info/dev_pm`
Read UFS device gear information such as HS_GEAR3, HS_GEAR4	`cat /sys/devices/platform/soc@0/1d84000.ufshc/power_info/gear`
Read UFS device number of lanes	`cat /sys/devices/platform/soc@0/1d84000.ufshc/power_info/lane`
Read UFS device link state, ACTIVE or HIBERN8	`cat /sys/devices/platform/soc@0/1d84000.ufshc/power_info/link_state`
Read UFS device rate information such as Rate A or B	`cat /sys/devices/platform/soc@0/1d84000.ufshc/power_info/rate`
Read UFS device descriptor information	`ls /sys/devices/platform/soc@0/1d84000.ufshc/device_descriptor`
Read UFS device health descriptor information	`ls /sys/devices/platform/soc@0/1d84000.ufshc/health_descriptor`
Read UFS device runtime status information active or suspended	`cat /sys/devices/platform/soc@0/1d84000.ufshc/power/runtime_status`
Find and/or modify the SPM/RPM level	`cat /sys/devices/platform/soc@0/1d84000.ufshc/rpm_lvl` `cat /sys/devices/platform/soc@0/1d84000.ufshc/spm_lvl`

SD card state commands

Before running the SD card state commands, identify the MMC host controller instance number and its physical address.

Determine the MMC instance number

The mmc<N> index used in debugfs paths such as /sys/kernel/debug/mmc1/err_stats is assigned by the Linux kernel MMC subsystem at boot time. The index is read directly from the aliases node in the board Device Tree (DTSI/DTS). The board DTSI assigns a fixed index to each SDHCI controller:

/ {
    aliases {
        mmc0 = &sdhc_1;   /* eMMC controller  → /sys/kernel/debug/mmc0/ */
        mmc1 = &sdhc_2;   /* SD card controller → /sys/kernel/debug/mmc1/ */
    };
};

The kernel reads this alias at probe time using of_alias_get_id(dev->of_node, "mmc") in mmc_alloc_host() (drivers/mmc/core/host.c), and sets the host device name with dev_set_name(&host->class_dev, "mmc%d", index). This name becomes the debugfs directory under /sys/kernel/debug/. To verify the mmc<N> index on a running system:

Enumerate MMC Host Controllers.
ls -l /sys/class/mmc_host
Identify the MMC physical address.
readlink -f /sys/class/mmc_host/mmc*
Confirm the index by checking the symlink target. For example, if the SD card SDHCI controller is at physical address 8804000, the output of step 2 will show a path containing 8804000.mmc under the mmc1 symlink, confirming the index is 1.

The mmc<N> index is platform-specific and is defined in the board DTSI aliases node. Always verify the index for your target platform before using the debugfs commands below.

Required SD card state information	Command
Read SD card error stats information	`cat /sys/kernel/debug/mmc1/err_stats`
Read SD card latest error state details	`cat /sys/kernel/debug/mmc1/err_state`
Check the current running clock details	`cat /sys/kernel/debug/mmc1/clock`
Read the SD card runtime status information (active or suspended)	`cat /sys/devices/platform/soc@0/<mmc_addr>.mmc/power/runtime_status`
Read SD card auto suspend delay time	`cat /sys/devices/platform/soc@0/<mmc_addr>.mmc/power/autosuspend_delay_ms`
Read SD card runtime active time	`cat /sys/devices/platform/soc@0/<mmc_addr>.mmc/power/runtime_active_time`
Read SD card runtime suspend time	`cat /sys/devices/platform/soc@0/<mmc_addr>.mmc/power/runtime_suspended_time`
Read SD card uevent details	`cat /sys/devices/platform/soc@0/<mmc_addr>.mmc/uevent`

NVMe state commands

Required NVMe card state information	Command
View device model name	`cat /sys/class/nvme/nvme0/model`
View device serial number	`cat /sys/class/nvme/nvme0/serial`
View current firmware version	`cat /sys/class/nvme/nvme0/firmware_rev`
View namespace identifier	`cat /sys/class/nvme/nvme0/nvme0n1/nsid`
View namespace size	`cat /sys/class/nvme/nvme0/nvme0n1/size`
View the offset in bytes to align the start of the NVMe namespace to the optimal I/O boundary	`cat /sys/class/nvme/nvme0/nvme0n1/alignment_offset`
View queue depth	`cat /sys/class/nvme/nvme0/queue_count`

eMMC node commands

The mmc0 index in /sys/kernel/debug/mmc0/ is assigned by the aliases node in the board DTSI, where mmc0 = &sdhc_1 maps the eMMC SDHCI controller to index 0. See Determine the MMC instance number for details.

Description	Command
eMMC error stats information	`cat /sys/kernel/debug/mmc0/err_stats`
eMMC latest error state details	`cat /sys/kernel/debug/mmc0/err_state`
Current running clock details of an eMMC	`cat /sys/kernel/debug/mmc0/clock`
eMMC runtime status information	`cat /sys/devices/platform/soc@0/<sdhci_addr>.mmc/power/runtime_status`
eMMC auto suspend delay time	`cat /sys/devices/platform/soc@0/<sdhci_addr>.mmc/power/autosuspend_delay_ms`
eMMC runtime active time	`cat /sys/devices/platform/soc@0/<sdhci_addr>.mmc/power/runtime_active_time`
eMMC runtime suspend time	`cat /sys/devices/platform/soc@0/<sdhci_addr>.mmc/power/runtime_suspended_time`
eMMC uevent details	`cat /sys/devices/platform/soc@0/<sdhci_addr>.mmc/uevent`

Update the <sdhci_addr> values based on the SDHCI physical address of the chip products.Example:

Qualcomm Dragonwing™ IQ-615: 7c4000
Qualcomm Dragonwing™ IQ-8275: 87c4000
Qualcomm Dragonwing™ IQ-9075: 7c4000

Introduction

Architecture

Key Documents

Technologies

System

Release Notes

UFS device state commands

SD card state commands

Determine the MMC instance number

NVMe state commands

eMMC node commands