linux-kernel - Re: [RFC PATCH v3 1/1] scsi: ufs: Enable power management for wlun

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Date:   Wed, 17 Feb 2021 14:29:40 -0800
From:   Asutosh Das <asutoshd@...eaurora.org>
To:     Avri Altman <Avri.Altman@....com>
Cc:     "cang@...eaurora.org" <cang@...eaurora.org>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "stern@...land.harvard.edu" <stern@...land.harvard.edu>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Bean Huo <beanhuo@...ron.com>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        Kiwoong Kim <kwmad.kim@...sung.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Satya Tangirala <satyat@...gle.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v3 1/1] scsi: ufs: Enable power management for wlun

On Tue, Feb 16 2021 at 09:44 -0800, Asutosh Das wrote:
>On Sat, Feb 13 2021 at 13:37 -0800, Avri Altman wrote:
>>>+       } else {
>>Is it possible to get here?
>>Scsi_scan_host is called only after successful add_wluns
>
>It looks so.
>scsi 0:0:0:49488: Link setup for lun - ufshcd_setup_links
>[...]
>Call trace:
>dump_backtrace+0x0/0x1d4
>show_stack+0x18/0x24
>dump_stack+0xc4/0x144
>ufshcd_setup_links+0xd8/0x100
>ufshcd_slave_alloc+0x134/0x1a0
>scsi_alloc_sdev+0x1c0/0x230
>scsi_probe_and_add_lun+0xc0/0xd48
>__scsi_add_device+0xc0/0x138
>ufshcd_scsi_add_wlus+0x30/0x1c0
>ufshcd_async_scan+0x58/0x240
>async_run_entry_fn+0x48/0x128
>process_one_work+0x1f0/0x470
>worker_thread+0x26c/0x4c8
>kthread+0x13c/0x320
>ret_from_fork+0x10/0x18
>
>>
>>>+               /* device wlun is probed */
>>>+               hba->luns_avail--;
>>>+       }
>>>+}
>>>+
>>
>>
>>>
>>> /**
>>>@@ -7254,6 +7312,14 @@ static int ufshcd_scsi_add_wlus(struct ufs_hba
>>>*hba)
>>>                goto out;
>>>        }
>>>        ufshcd_blk_pm_runtime_init(hba->sdev_ufs_device);
>>>+       /*
>>>+        * A pm_runtime_put_sync is invoked when this device enables
>>>blk_pm_runtime
>>>+        * & would suspend the device-wlun upon timer expiry.
>>>+        * But suspending device wlun _may_ put the ufs device in the pre-defined
>>>+        * low power mode (SSU <rpm_lvl>). Probing of other luns may fail then.
>>>+        * Don't allow this suspend until all the luns have been probed.
>>Maybe add one more sentence: see pm_runtime_mark_last_busy in ufshcd_setup_links
>Done.
>
>>
>>
>>
>>>-       ufshcd_clear_ua_wluns(hba);
>>Are there any callers left to ufshcd_clear_ua_wluns?
>>Can it be removed?
>Let me check.
>
I don't think this can be removed.
The reasoning behind this call as per the commit message indicates that if
there's a reset this request_sense is needed to clear uac.

In pm level 5, the reset would still happen. So I guess this is needed.
Please let me know if I'm missing something here.
The commit message didn't have much details otherwise.



>
>>
>>>+       if (hba->wlun_dev_clr_ua)
>>>+               ufshcd_clear_ua_wlun(hba, UFS_UPIU_UFS_DEVICE_WLUN);
>>>
>>>        cmd[4] = pwr_mode << 4;