Re: [PATCH V4 11/17] scsi: ufs: add UFS power management support

Dolev Raviv
2014-09-23T12:57:32Z

>> /**
>> * ufshcd_slave_alloc - handle initial SCSI device configurations
>> * @sdev: pointer to SCSI device
>> @@ -2232,6 +2403,21 @@ static int ufshcd_slave_alloc(struct scsi_device
>> *sdev)
>>
>> ufshcd_set_queue_depth(sdev);
>>
>> + ufshcd_get_lu_power_on_wp_status(hba, sdev);
>> +
>> + /*
>> + * For selecting the UFS device power mode (Active / UFS_Sleep /
>> + * UFS_PowerDown), SCSI power management command (START STOP UNIT)
>> + * needs to be sent to a "UFS device" Well known Logical Unit (W-LU).
>> + * As this command would be sent during the UFS host controller
>> + * runtime/system PM callbacks, we need a reference to "scsi_device"
>> + * associated to "UFS device" W-LU. This change saves the
>> "scsi_device"
>> + * reference for "UFS device" W-LU during slave_configure() callback
>> + * from SCSI mid layer.
>> + */
>> + if (ufshcd_scsi_to_upiu_lun(sdev->lun) == UFS_UPIU_UFS_DEVICE_WLUN)
>> + hba->sdev_ufs_device = sdev;
>> +
>
> Storing the pointer in slave_alloc is not safe as you don't known if the
> probing was successful. In addition you really need a reference to a
> scsi_device that you store somewhere as a user could easily delete the
> device through sysfs, which any access to it invalid.
>
> As mention earlier you should just add this wlun using __scsi_device_add
> which gives you a pointer and a reference to the fully probed device.

Sounds reasonable, I'll coordinate it with the previous patch.

>
>> +static int
>> +ufshcd_send_request_sense(struct ufs_hba *hba, struct scsi_device *sdp)
>> +{
>> + unsigned char cmd[6] = {REQUEST_SENSE,
>> + 0,
>> + 0,
>> + 0,
>> + SCSI_SENSE_BUFFERSIZE,
>> + 0};
>> + char *buffer;
>> + int ret;
>> +
>> + buffer = kzalloc(SCSI_SENSE_BUFFERSIZE, GFP_KERNEL);
>> + if (!buffer) {
>> + ret = -ENOMEM;
>> + goto out;
>> + }
>> +
>> + ret = scsi_execute_req_flags(sdp, cmd, DMA_FROM_DEVICE, buffer,
>> + SCSI_SENSE_BUFFERSIZE, NULL,
>> + msecs_to_jiffies(1000), 3, NULL, REQ_PM);
>> + if (ret)
>> + pr_err("%s: failed with err %d\n", __func__, ret);
>> +
>> + kfree(buffer);
>> +out:
>> + return ret;
>> +}
>
> It would be good to have an explanation why you need to call
> REQUEST SENSE from the driver. OR your own START STOP later one. This
> all seems very much against the normal model of operation for SCSI
> devices.
>

Let me rephrase the explanation from the commit message:
We issue request sense before sending START_STOP_UNIT to the device
well-known logical unit (w-lun) to make sure that the device w-lun
unit attention condition is cleared. Otherwise START_STOP_UNIT will fail.

As mentioned in my previous mail (in response to [9/17] patch comments),
UFS driver power management is controlled via device W-LUN during the
suspend process.
As documented in the comment above: "
* For selecting the UFS device power mode (Active / UFS_Sleep /
* UFS_PowerDown), SCSI power management command (START STOP UNIT)
* needs to be sent to a "UFS device" Well known Logical Unit (W-LU).
* As this command would be sent during the UFS host controller
* runtime/system PM callbacks, ....
"
Do you have another suggestion for making it compatible to other scsi
drivers?
Would you prefer this logic would go into core scsi?