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

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Date:   Mon, 4 Jan 2021 11:15:23 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     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
Cc:     Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.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 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.

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?