Re: [PATCH v4 01/10] scsi: ufs: Rename flags pm_op_in_progress and is_sys_suspended

From: Can Guo <cang@codeaurora.org>
To: Bart Van Assche <bvanassche@acm.org>
Cc: asutoshd@codeaurora.org, nguyenb@codeaurora.org,
	hongwus@codeaurora.org, ziqichen@codeaurora.org,
	linux-scsi@vger.kernel.org, kernel-team@android.com,
	Andy Gross <agross@kernel.org>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	Alim Akhtar <alim.akhtar@samsung.com>,
	Avri Altman <avri.altman@wdc.com>,
	"James E.J. Bottomley" <jejb@linux.ibm.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	Stanley Chu <stanley.chu@mediatek.com>,
	Bean Huo <beanhuo@micron.com>, Jaegeuk Kim <jaegeuk@kernel.org>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Kiwoong Kim <kwmad.kim@samsung.com>,
	Satya Tangirala <satyat@google.com>,
	"open list:ARM/QUALCOMM SUPPORT" <linux-arm-msm@vger.kernel.org>,
	open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 01/10] scsi: ufs: Rename flags pm_op_in_progress and is_sys_suspended
Date: Thu, 24 Jun 2021 10:02:46 +0800	[thread overview]
Message-ID: <932ce816be805e4cca2c5beee8627918@codeaurora.org> (raw)
In-Reply-To: <c7c5d95e-8a69-dfef-44ea-bfcadd6ea5d5@acm.org>

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.