linux-kernel - Re: [PATCH RFC v4 1/1] scsi: ufs: Fix ufs power down/on specs violation

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Message-ID: <bb0a37d5825eec1ec03a1ba1104fec86@codeaurora.org>
Date:   Tue, 05 Jan 2021 18:06:12 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Ziqi Chen <ziqichen@...eaurora.org>, asutoshd@...eaurora.org,
        nguyenb@...eaurora.org, hongwus@...eaurora.org,
        rnayak@...eaurora.org, vinholikatti@...il.com,
        jejb@...ux.vnet.ibm.com, martin.petersen@...cle.com,
        linux-scsi@...r.kernel.org, kernel-team@...roid.com,
        saravanak@...gle.com, salyzyn@...gle.com, kwmad.kim@...sung.com,
        stanley.chu@...iatek.com, Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        Andy Gross <agross@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Bean Huo <beanhuo@...ron.com>,
        Bart Van Assche <bvanassche@....org>,
        Satya Tangirala <satyat@...gle.com>,
        "moderated list:UNIVERSAL FLASH STORAGE HOST CONTROLLER DRIVER..." 
        <linux-mediatek@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:ARM/QUALCOMM SUPPORT" <linux-arm-msm@...r.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH RFC v4 1/1] scsi: ufs: Fix ufs power down/on specs
 violation

On 2021-01-05 15:33, Adrian Hunter wrote:
> On 5/01/21 9:28 am, Can Guo wrote:
>> On 2021-01-05 15:16, Adrian Hunter wrote:
>>> On 4/01/21 8:55 pm, Bjorn Andersson wrote:
>>>> On Mon 04 Jan 03:15 CST 2021, Adrian Hunter wrote:
>>>> 
>>>>> On 22/12/20 3:49 pm, Ziqi Chen wrote:
>>>>>> As per specs, e.g, JESD220E chapter 7.2, while powering
>>>>>> off/on the ufs device, RST_N signal and REF_CLK signal
>>>>>> should be between VSS(Ground) and VCCQ/VCCQ2.
>>>>>> 
>>>>>> To flexibly control device reset line, refactor the function
>>>>>> ufschd_vops_device_reset(sturct ufs_hba *hba) to ufshcd_
>>>>>> vops_device_reset(sturct ufs_hba *hba, bool asserted). The
>>>>>> new parameter "bool asserted" is used to separate device reset
>>>>>> line pulling down from pulling up.
>>>>> 
>>>>> This patch assumes the power is controlled by voltage regulators, 
>>>>> but
>>>>> for us
>>>>> it is controlled by firmware (ACPI), so it is not correct to change 
>>>>> RST_n
>>>>> for all host controllers as you are doing.
>>>>> 
>>>>> Also we might need to use a firmware interface for device reset, in 
>>>>> which
>>>>> case the 'asserted' value doe not make sense.
>>>>> 
>>>> 
>>>> Are you saying that the entire flip-flop-the-reset is a single 
>>>> firmware
>>>> operation in your case?
>>> 
>>> Yes
>>> 
>>>>                         If you look at the Mediatek driver, the
>>>> implementation of ufs_mtk_device_reset_ctrl() is a jump to firmware.
>>>> 
>>>> 
>>>> But perhaps "asserted" isn't the appropriate English word for saying
>>>> "the reset is in the resetting state"?
>>>> 
>>>> I just wanted to avoid the use of "high"/"lo" as if you look at the
>>>> Mediatek code they pass the expected line-level to the firmware, 
>>>> while
>>>> in the Qualcomm code we pass the logical state to the GPIO code 
>>>> which is
>>>> setup up as "active low" and thereby flip the meaning before hitting 
>>>> the
>>>> pad.
>>>> 
>>>>> Can we leave the device reset callback alone, and instead introduce 
>>>>> a new
>>>>> variant operation for setting RST_n to match voltage regulator 
>>>>> power
>>>>> changes?
>>>> 
>>>> Wouldn't this new function just have to look like the proposed 
>>>> patches?
>>>> In which case for existing platforms we'd have both?
>>>> 
>>>> How would you implement this, or would you simply skip implementing
>>>> this?
>>> 
>>> Functionally, doing a device reset is not the same as adjusting 
>>> signal
>>> levels to meet power up/off ramp requirements.  However, the issue is 
>>> that
>>> we do not use regulators, so the power is not necessarily being 
>>> changed at
>>> those points, and we definitely do not want to reset instead of 
>>> entering
>>> DeepSleep for example.
>>> 
>>> Off the top of my head, I imagine something like a callback called
>>> ufshcd_vops_prepare_power_ramp(hba, bool on) which is called only if
>>> hba->vreg_info->vcc is not NULL.
>> 
>> Hi Adrian,
>> 
>> I don't see you have the vops device_reset() implemented anywhere in
>> current code base, how is this change impacting you? Do I miss 
>> anything
>> or are you planning to push a change which implements device_reset() 
>> soon?
> 
> At some point, yes.

OK, then we don't even have to add a new vops, just go back to version 
#1 to
use ufshcd_vops_suspend() to control the device_reset. We took the hard 
way
because we wanted to fix it for all users.