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

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Message-ID: <b82dd5f1-179c-6834-9d8f-88005b74ce51@intel.com>
Date:   Tue, 5 Jan 2021 09:16:54 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Ziqi Chen <ziqichen@...eaurora.org>, asutoshd@...eaurora.org,
        nguyenb@...eaurora.org, cang@...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 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.