Re: [PATCH v1 4/4] scsi: ufs: Fix WriteBooster flush during runtime suspend

[Stanley Chu]

Hi Asutosh,

On Thu, 2020-05-14 at 10:23 +0800, Stanley Chu wrote:
> Hi Asutosh,
> 
> On Wed, 2020-05-13 at 12:31 -0700, Asutosh Das (asd) wrote:
> > On 5/12/2020 3:47 AM, Stanley Chu wrote:
> > > Currently UFS host driver promises VCC supply if UFS device
> > > needs to do WriteBooster flush during runtime suspend.
> > > 
> > > However the UFS specification mentions,
> > > 
> > > "While the flushing operation is in progress, the device is
> > > in Active power mode."
> > > 
> > > Therefore UFS host driver needs to promise more: Keep UFS
> > > device as "Active power mode", otherwise UFS device shall not
> > > do any flush if device enters Sleep or PowerDown power mode.
> > > 
> > > Fix this by not changing device power mode if WriteBooster
> > > flush is required in ufshcd_suspend().
> > > 
> > > Signed-off-by: Stanley Chu <stanley.chu@xxxxxxxxxxxx>
> > > ---
> > >   drivers/scsi/ufs/ufs.h    |  1 -
> > >   drivers/scsi/ufs/ufshcd.c | 39 +++++++++++++++++++--------------------
> > >   2 files changed, 19 insertions(+), 21 deletions(-)
> > > 
> > > diff --git a/drivers/scsi/ufs/ufs.h b/drivers/scsi/ufs/ufs.h
> > > index b3135344ab3f..9e4bc2e97ada 100644
> > > --- a/drivers/scsi/ufs/ufs.h
> > > +++ b/drivers/scsi/ufs/ufs.h
> > > @@ -577,7 +577,6 @@ struct ufs_dev_info {
> > >   	u32 d_ext_ufs_feature_sup;
> > >   	u8 b_wb_buffer_type;
> > >   	u32 d_wb_alloc_units;
> > > -	bool keep_vcc_on;
> > >   	u8 b_presrv_uspc_en;
> > >   };
> > >   
> > > diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> > > index 169a3379e468..2d0aff8ac260 100644
> > > --- a/drivers/scsi/ufs/ufshcd.c
> > > +++ b/drivers/scsi/ufs/ufshcd.c
> > > @@ -8101,8 +8101,7 @@ static void ufshcd_vreg_set_lpm(struct ufs_hba *hba)
> > >   	    !hba->dev_info.is_lu_power_on_wp) {
> > >   		ufshcd_setup_vreg(hba, false);
> > >   	} else if (!ufshcd_is_ufs_dev_active(hba)) {
> > > -		if (!hba->dev_info.keep_vcc_on)
> > > -			ufshcd_toggle_vreg(hba->dev, hba->vreg_info.vcc, false);
> > > +		ufshcd_toggle_vreg(hba->dev, hba->vreg_info.vcc, false);
> > >   		if (!ufshcd_is_link_active(hba)) {
> > >   			ufshcd_config_vreg_lpm(hba, hba->vreg_info.vccq);
> > >   			ufshcd_config_vreg_lpm(hba, hba->vreg_info.vccq2);
> > > @@ -8172,6 +8171,7 @@ static int ufshcd_suspend(struct ufs_hba *hba, enum ufs_pm_op pm_op)
> > >   	enum ufs_pm_level pm_lvl;
> > >   	enum ufs_dev_pwr_mode req_dev_pwr_mode;
> > >   	enum uic_link_state req_link_state;
> > > +	bool keep_curr_dev_pwr_mode = false;
> > >   
> > >   	hba->pm_op_in_progress = 1;
> > >   	if (!ufshcd_is_shutdown_pm(pm_op)) {
> > > @@ -8226,28 +8226,27 @@ static int ufshcd_suspend(struct ufs_hba *hba, enum ufs_pm_op pm_op)
> > >   			/* make sure that auto bkops is disabled */
> > >   			ufshcd_disable_auto_bkops(hba);
> > >   		}
> > > +
> > Unnecessary newline, perhaps?
> 
> Yap, I will remove it in next version.
> 
> > >   		/*
> > > -		 * With wb enabled, if the bkops is enabled or if the
> > > -		 * configured WB type is 70% full, keep vcc ON
> > > -		 * for the device to flush the wb buffer
> > > +		 * If device needs to do BKOP or WB buffer flush, keep device
> > > +		 * power mode as "active power mode" and its VCC supply.
> > >   		 */
> > > -		if ((hba->auto_bkops_enabled && ufshcd_is_wb_allowed(hba)) ||
> > > -		    ufshcd_wb_keep_vcc_on(hba))
> > > -			hba->dev_info.keep_vcc_on = true;
> > > -		else
> > > -			hba->dev_info.keep_vcc_on = false;
> > > -	} else {
> > > -		hba->dev_info.keep_vcc_on = false;
> > > +		keep_curr_dev_pwr_mode = hba->auto_bkops_enabled ||
> > > +			ufshcd_wb_keep_vcc_on(hba);
> > Should the device be in UFS_ACTIVE_PWR_MODE to perform auto-bkops?
> > 
> > Also, is it needed to keep the device in UFS_ACTIVE_PWR_MODE , if flush 
> > on hibern8 is enabled and the link is being put to hibern8 mode during 
> > runtime-suspend? Perhaps that should also be factored in here?
> 
> Both auto-bkops and WriteBooster flush during Hibern8 need device power
> mode to be "Active Power Mode".
> 
> For auto-bkops, the spec mentions,
> 
> "If the background operations enable bit is set and the device is in
> Active power mode or Idle power mode, then the device is allowed to
> execute any internal operations."
> 
> For WriteBooster flush during Hibern8, the spec mentions,
> 
> "While the flushing operation is in progress, the device is in Active
> power mode."
> 
> Therefore here we can use an unified "keep_curr_dev_pwr_mode" to
> indicate the same requirements of above both features.
> 
> Besides, both operations may access flash array inside UFS device thus
> VCC supply shall be also kept.
> 
> Before this patch, the original code will keep device power mode (stay
> in Active Power Mode) if hba->auto_bkops_enabled is set as true during
> runtime-suspend with UFSHCD_CAP_AUTO_BKOPS_SUSPEND capability is
> enabled. This patch will not change this decision, just add
> "WriteBooster flush during Hibern8" feature as another condition to do
> so.
> 
> Thank you so much to remind me that "Link shall be put in Hibern8" is a
> necessary condition for "WriteBooster flush during Hibern8". I will add
> more checking for keep_curr_dev_pwr_mode to prevent unnecessary power
> drain.  
> 
> > >   	}
> > >   
> > > -	if ((req_dev_pwr_mode != hba->curr_dev_pwr_mode) &&
> > > -	    ((ufshcd_is_runtime_pm(pm_op) && !hba->auto_bkops_enabled) ||
> > > -	    !ufshcd_is_runtime_pm(pm_op))) {
> > > -		/* ensure that bkops is disabled */
> > > -		ufshcd_disable_auto_bkops(hba);
> > > -		ret = ufshcd_set_dev_pwr_mode(hba, req_dev_pwr_mode);
> > > -		if (ret)
> > > -			goto enable_gating;
> > > +	if (req_dev_pwr_mode != hba->curr_dev_pwr_mode) {
> > > +		if ((ufshcd_is_runtime_pm(pm_op) && !hba->auto_bkops_enabled) ||
> > > +		    !ufshcd_is_runtime_pm(pm_op)) {
> > > +			/* ensure that bkops is disabled */
> > > +			ufshcd_disable_auto_bkops(hba);
> > > +		}
> > > +
> > > +		if (!keep_curr_dev_pwr_mode) {
> > > +			ret = ufshcd_set_dev_pwr_mode(hba, req_dev_pwr_mode);
> > 
> > Now, when the WB buffer is completely flushed out, the device should be 
> > put back into UFS_SLEEP_PWR_MODE or UFS_POWERDOWN_PWR_MODE. Say, the 
> > device buffer has to be flushed and during runtime-suspend, the device 
> > is put to UFS_ACTIVE_PWR_MODE and Vcc is kept ON; the device doesn't 
> > resume nor does the system enters suspend for a very long time, and with 
> > AH8 and hibern8 disabled, there will be an unnecessary power drain for 
> > that much time.

Another thought is that if keep_curr_dev_pwr_mode will be set as true
only if link is put in Hibern8 or Auto-Hibern8 is enabled. By this way,
the power consumption shall be very small after flush or auto-bkop is
finished.

Then the checking of flush status during runtime-suspend may be not
necessary.

> > 
> > How about a periodic interval checking of flush status if 
> > keep_curr_dev_pwr_mode evaluates to be true?
> 
> This is a good point!
> 
> The same thing also happens for auto-bkops. How about add a timer to
> leave runtime suspend if keep_curr_dev_pwr_mode is set as true? This is
> simple and also favors power. The timeout value could be adjustable
> according to the available WriteBooster buffer size.
> 
> A periodic interval checking of flush status needs to re-activate link
> to communicate with the device. This would be tricky and the
> re-activation flow is just like runtime-resume.
> 
> What would you think?
> 
> Thanks.
> Stanley Chu
> 
> 
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