linux-kernel - RE: [PATCH v1 1/1] scsi: ufshcd: Properly set the device Icc Level

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Date:   Thu, 10 Sep 2020 10:02:05 +0000
From:   Avri Altman <Avri.Altman@....com>
To:     "nguyenb@...eaurora.org" <nguyenb@...eaurora.org>,
        "cang@...eaurora.org" <cang@...eaurora.org>,
        "asutoshd@...eaurora.org" <asutoshd@...eaurora.org>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>
CC:     "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Bean Huo <beanhuo@...ron.com>,
        Bart Van Assche <bvanassche@....org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v1 1/1] scsi: ufshcd: Properly set the device Icc Level

> 
> On 2020-08-31 18:19, Bao D. Nguyen wrote:
> > UFS version 3.0 and later devices require Vcc and Vccq power supplies
> > with Vccq2 being optional. While earlier UFS version 2.0 and 2.1
> > devices, the Vcc and Vccq2 are required with Vccq being optional.
> > Check the required power supplies used by the device
> > and set the device's supported Icc level properly.
Practically you are correct - most flash vendors moved in UFS3.1 to 1.2 supply instead of 1.8.
However, the host should provide all 3 supplies to the device because - 
a) A flash vendor might want to still use 1.8 in its UFS3.1 device, and
b) We should allow a degenerated configurations, e.g. 3.1 devices, that are degenerated to 2.1 or 2.2

That said, I think we can entirely remove the check in the beginning of the function,
But not because the spec allows it, but because each supply is explicitly checked later on,
before reading its applicable max current entry in the power descriptor.

Thanks,
Avri