Re: [PATCH v2 5/6] misc: amd-sbi: Add SBTSI ioctl register transfer interface

["Gupta, Akshay" <Akshay.Gupta@amd.com>]

On 5/15/2026 7:41 PM, Guenter Roeck wrote:
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>
>
> On 5/15/26 06:45, Akshay Gupta wrote:
>> From: Prathima <Prathima.Lk@amd.com>
>>
>> Implement IOCTL interface for SB-TSI driver to enable userspace access
>> to TSI register read/write operations through the AMD Advanced Platform
>> Management Link (APML) protocol.
>> Add an ioctl command (SBTSI_IOCTL_REG_XFER_CMD) that accepts a register
>> address, data byte, and direction flag. Serialize access with a mutex
>> shared between the hwmon and ioctl paths to prevent concurrent bus
>> transactions from corrupting register state.
>>
>> Reviewed-by: Akshay Gupta <Akshay.Gupta@amd.com>
>> Signed-off-by: Prathima <Prathima.Lk@amd.com>
>> ---
>> Changes since v1:
>> - Use of devm_mutex_init in place of mutex_init
>> - Use of guard_mutex in place of mutex_lock()/mutex_unlock()
>> - Use of devm_add_action_or_reset() for clean removal
>>
>>    drivers/hwmon/sbtsi_temp.c      |  6 +++
>>    drivers/misc/amd-sbi/tsi-core.c | 84 ++++++++++++++++++++++++++++++++-
>>    drivers/misc/amd-sbi/tsi-core.h | 15 ++++++
>>    drivers/misc/amd-sbi/tsi.c      | 20 ++++++--
>>    include/linux/misc/tsi.h        |  8 ++++
>>    include/uapi/misc/amd-apml.h    | 23 +++++++++
>>    6 files changed, 151 insertions(+), 5 deletions(-)
>>    create mode 100644 drivers/misc/amd-sbi/tsi-core.h
>>
>> diff --git a/drivers/hwmon/sbtsi_temp.c b/drivers/hwmon/sbtsi_temp.c
>> index d7ae986d824c..00e982f4c716 100644
>> --- a/drivers/hwmon/sbtsi_temp.c
>> +++ b/drivers/hwmon/sbtsi_temp.c
>> @@ -64,12 +64,15 @@ static inline void sbtsi_mc_to_reg(s32 temp, u8 *integer, u8 *decimal)
>>    /*
>>     * Read integer and decimal parts of an SB-TSI temperature register pair
>>     * The read order is determined by the ReadOrder bit to ensure atomic latching.
>> + * The mutex protects against concurrent access to the shared I2C/I3C bus by
>> + * the hwmon sysfs and a userspace ioctl
>>     */
>>    static int sbtsi_temp_read(struct sbtsi_data *data, u8 reg1, u8 reg2,
>>                           u8 *val1, u8 *val2)
>>    {
>>        int ret;
>>
>> +     guard(mutex)(&data->lock);
> I would suggest to hide this behind access functions such as sbtsi_lock(),
> sbtsi_unlock(), and the matching guard functions. That can be done in a
> separate patch; it should not be necessary to include hwmon in the patch
> introducing the ioctl.
>
> Thanks,
> Guenter

Thank you for the feedback, Guenter.

In the next version, we will address this by implementing the matching 
guard function in the ioctl patch and creating a new patch for hwmon.

>