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Date:   Wed, 20 Nov 2019 04:14:43 +0000
From:   cang@codeaurora.org
To:     Avri Altman <Avri.Altman@wdc.com>
Cc:     Can Guo <cang@qti.qualcomm.com>, asutoshd@codeaurora.org,
        nguyenb@codeaurora.org, rnayak@codeaurora.org,
        linux-scsi@vger.kernel.org, kernel-team@android.com,
        saravanak@google.com, salyzyn@google.com,
        Alim Akhtar <alim.akhtar@samsung.com>,
        Pedro Sousa <pedrom.sousa@synopsys.com>,
        "James E.J. Bottomley" <jejb@linux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Stanley Chu <stanley.chu@mediatek.com>,
        Tomas Winkler <tomas.winkler@intel.com>,
        open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 2/4] scsi: ufs: Update VCCQ2 and VCCQ min/max voltage
 hard codes
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On 2019-11-19 20:41, Avri Altman wrote:
>> 
>> On 2019-11-18 15:15, Avri Altman wrote:
>> >>
>> >> From: Can Guo <cang@codeaurora.org>
>> >>
>> >> Per UFS 3.0 JEDEC standard, the VCCQ2 min voltage is 1.7v and the
>> >> VCCQ voltage range is 1.14v ~ 1.26v. Update their hard codes
>> >> accordingly to make sure they work in a safe range compliant for ver
>> >> 1.0/2.0/2.1/3.0 UFS devices.
>> > So to keep it safe, we need to use largest range:
>> > min_uV = min over all spec ranges, and max_uV = max over all spec
>> > ranges.
>> > Meaning leave it as it is if we want to be backward compatible with
>> > UFS1.0.
>> >
>> > Thanks,
>> > Avri
>> >
>> 
>> Hi Avri,
>> 
>> Sorry I don't quite follow you here.
>> Leaving it as it is means for UFS2.1 devices, when boot up, if we call
>> regulator_set_voltage(1.65, 1.95) to setup its VCCQ2,
>> regulator_set_voltage() will
>> give you 1.65v on VCCQ2 if the voltage level of this regulator is 
>> wider, say (1.60,
>> 1.95).
>> Meaning you will finally set 1.65v to VCCQ2. But 1.65v is out of spec 
>> for UFS
>> v2.1 as it requires min voltage to be 1.7v on VCCQ2. So, the smallest 
>> range is
>> safe.
>> Of course, in real board design, the regulator's voltage level is 
>> limited/designed
>> by power team to be in a safe range, say (1.8, 1.92), so that calling
>> regulator_set_voltage(1.65, 1.95) still gives you 1.8v. But it does 
>> not mean the
>> current hard codes are compliant for all UFS devices.
> You are correct - the narrowest the range the better - as long as you
> don't cross the limits of previous spec.
> So changing 1.1 -> 1.14  and 1.65 -> 1.7 is fine.
> While at it, Vccq max in UFS3.0 is 1.26, why not change 1.3 -> 1.26,
> like you indicated in your commit log?
> 
> Thanks,
> Avri
> 

Thank you Avri, sorry I missed the change to max voltage of VCCQ, I
will update it in the next version.

Best Regards,
Can Guo.

>> 
>> Best Regards,
>> Can Guo.
>> 
>> >>
>> >> Signed-off-by: Can Guo <cang@codeaurora.org>
>> >> ---
>> >>  drivers/scsi/ufs/ufs.h | 4 ++--
>> >>  1 file changed, 2 insertions(+), 2 deletions(-)
>> >>
>> >> diff --git a/drivers/scsi/ufs/ufs.h b/drivers/scsi/ufs/ufs.h index
>> >> 385bac8..9df4f4d
>> >> 100644
>> >> --- a/drivers/scsi/ufs/ufs.h
>> >> +++ b/drivers/scsi/ufs/ufs.h
>> >> @@ -500,9 +500,9 @@ struct ufs_query_res {
>> >>  #define UFS_VREG_VCC_MAX_UV       3600000 /* uV */
>> >>  #define UFS_VREG_VCC_1P8_MIN_UV    1700000 /* uV */
>> >>  #define UFS_VREG_VCC_1P8_MAX_UV    1950000 /* uV */
>> >> -#define UFS_VREG_VCCQ_MIN_UV      1100000 /* uV */
>> >> +#define UFS_VREG_VCCQ_MIN_UV      1140000 /* uV */
>> >>  #define UFS_VREG_VCCQ_MAX_UV      1300000 /* uV */
>> >> -#define UFS_VREG_VCCQ2_MIN_UV     1650000 /* uV */
>> >> +#define UFS_VREG_VCCQ2_MIN_UV     1700000 /* uV */
>> >>  #define UFS_VREG_VCCQ2_MAX_UV     1950000 /* uV */
>> >>
>> >>  /*
>> >> --
>> >> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora
>> >> Forum, a Linux Foundation Collaborative Project