linux-kernel - RE: [PATCH 1/2] scsi: ufs: Add DeepSleep feature

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Date:   Mon, 5 Oct 2020 08:02:13 +0000
From:   Avri Altman <Avri.Altman@....com>
To:     Adrian Hunter <adrian.hunter@...el.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        "James E . J . Bottomley" <jejb@...ux.ibm.com>
CC:     "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Alim Akhtar <alim.akhtar@...sung.com>
Subject: RE: [PATCH 1/2] scsi: ufs: Add DeepSleep feature

HI,

> Drivers that wish to support DeepSleep need to set a new capability flag
> UFSHCD_CAP_DEEPSLEEP and provide a hardware reset via the existing
>  ->device_reset() callback.
I would expect that this capability controls sending SSU 4, but it only controls the sysfs entry?

> 
> It is assumed that UFS devices with wspecversion >= 0x310 support
> DeepSleep.
> 
> The UFS specification says to set the IMMED (immediate) flag for the
> Start/Stop Unit command when entering DeepSleep. However some UFS
> devices object to that, which is addressed in a subsequent patch.
After failing to understand what the proper behavior should be with respect of the IMMED bit,
Although I read the applicable section few time, I gave up and consult our system guy,
Which is our jedec representative.  This is his answer:
"...
In order to avoid uncertainty - the host need to set IMMED bit to '0' (this is explicitly specified by the standard).
The device responds only after it switches to Pre-DeepSleep state. The host then switch to H8 and this would trigger the device to transition to DeepSleep state.
..."

So maybe the 2nd patch isn't really needed. 
Thanks,
Avri