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

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Date:   Tue, 5 Jan 2021 09:33:22 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Can Guo <cang@...eaurora.org>
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 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.