linux-kernel - Re: [PATCH v4 01/10] scsi: ufs: Rename flags pm_op_in_progress and is_sys

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Date:   Thu, 24 Jun 2021 10:02:46 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Bart Van Assche <bvanassche@....org>
Cc:     asutoshd@...eaurora.org, nguyenb@...eaurora.org,
        hongwus@...eaurora.org, ziqichen@...eaurora.org,
        linux-scsi@...r.kernel.org, kernel-team@...roid.com,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Bean Huo <beanhuo@...ron.com>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Kiwoong Kim <kwmad.kim@...sung.com>,
        Satya Tangirala <satyat@...gle.com>,
        "open list:ARM/QUALCOMM SUPPORT" <linux-arm-msm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 01/10] scsi: ufs: Rename flags pm_op_in_progress and
 is_sys_suspended

Hi Bart,

On 2021-06-24 04:57, Bart Van Assche wrote:
> On 6/23/21 1:05 PM, Bart Van Assche wrote:
>> On 6/23/21 12:35 AM, Can Guo wrote:
>>> Rename pm_op_in_progress and is_sys_suspended to 
>>> wlu_pm_op_in_progress and
>>> is_wlu_sys_suspended accordingly.
>> 
>> My understanding is that power management operations must be submitted
>> to one particular UFS WLUN (hba->sdev_ufs_device). That makes the 
>> "wlu_"
>> part of the new names redundant. In other words, I like the current
>> names better than the new names. Unless if I missed something, 
>> consider
>> dropping this patch.
> 
> Hi Can,
> 
> Reviewing later patches in this series made me realize that there are
> two families of suspend/resume functions. One family of functions
> operates at the platform level while the other family operates at the
> SCSI LUN level. My comments about the suspend/resume functions are as
> follows:
> - It seems redundant to me to have system suspend support at the SCSI
>   LUN level (__ufshcd_wl_suspend(hba, UFS_SYSTEM_PM)) and also at the
>   platform level. Since the platform device is a parent of the SCSI
>   WLUN, can system suspend/resume support be left out from
>   ufshcd_wl_pm_ops (or in other words, remove the .freeze and .thaw
>   callbacks)? Do we really need two calls from the power management
>   subsystem into the UFS driver for every system suspend and every
>   system resume?

Asutosh and Adrian should be the right persons to answer this, since
they've been working together on that huge change for 4 months -

https://lore.kernel.org/patchwork/patch/1417696/

In short, we need a dedicated suspend/resume ops for the UFS device
W-LU because one cannot send requests (not even PM requests) after the
device is runtime suspended - sending SSU cmds in hba suspend/resume
cannot pass through blk_queue_enter() as SSU cmd is sent to the UFS
device W-LU scsi device (by now it is runtime suspended) but not the
hba device.

Of course we can keep the old way and send the SSU cmd through a
request queue without block layer PM initialized (hba->cmd_queue for
example, by pointing cmd_queue->dev to the UFS device W-LU scsi device),
but that would look like a hack.

> - Because of the device links (device_link_add()), the ufschd_wl_*()
>   RPM callbacks are invoked after all LUNs have been suspended. I would
>   appreciate it if the "ufshcd_wl_" prefix would be changed into
>   "ufshcd_lun_" since that would make it more clear that these 
> callbacks
>   are associated with all LUNs and not only with the WLUN through which
>   power management commands are submitted.
> 

Sure, we will do that later.

Thanks,

Can Guo.

> Thanks,
> 
> Bart.