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

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Date:   Tue, 05 Jan 2021 15:28:47 +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 15:16, 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?

Thanks,
Can Guo.