linux-kernel - Re: [PATCH v1 2/2] scsi: ufs: core: Reduce the sleep before vcc can be powered on

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Message-ID: <2ce08f9f-af8c-4cac-8d66-97517eb18037@acm.org>
Date: Tue, 7 Oct 2025 09:19:44 -0700
From: Bart Van Assche <bvanassche@....org>
To: Peter Wang (王信友) <peter.wang@...iatek.com>,
 "avri.altman@....com" <avri.altman@....com>,
 "quic_cang@...cinc.com" <quic_cang@...cinc.com>,
 "quic_nitirawa@...cinc.com" <quic_nitirawa@...cinc.com>,
 "quic_nguyenb@...cinc.com" <quic_nguyenb@...cinc.com>,
 "manivannan.sadhasivam@...aro.org" <manivannan.sadhasivam@...aro.org>,
 "adrian.hunter@...el.com" <adrian.hunter@...el.com>,
 "martin.petersen@...cle.com" <martin.petersen@...cle.com>
Cc: "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
 "beanhuo@...ron.com" <beanhuo@...ron.com>,
 "alim.akhtar@...sung.com" <alim.akhtar@...sung.com>,
 "James.Bottomley@...senPartnership.com"
 <James.Bottomley@...senPartnership.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 2/2] scsi: ufs: core: Reduce the sleep before vcc can
 be powered on


On 10/7/25 12:04 AM, Peter Wang (王信友) wrote:
> On Fri, 2025-10-03 at 14:27 -0700, Bao D. Nguyen wrote:
>> With the current or recent offerings of ufs devices in the market, 
>> the requirement is 1ms. For example, the Kioxia datasheet says
>> "Vcc shall be kept less than 0.3V for at least 1ms before it goes
>> beyond 0.3V again". Similarly other vendors have this 1ms
>> requirement. So I believe this indicates the worst case scenario. 
>> I understand there may be very old devices that are upgrading the 
>> kernel only. In that case I don't know the specifics for these old
>> ufs parts as mentioned.
> 
> Hi Bao,
> 
> Please consider using module_param_cb to set the default
> delay to 2ms(or 1ms). At the same time, we should keep the
> flexibility for devices that may require a longer delay by
> allowing them to extend the delay through a module parameter.

Why a kernel module parameter? Why can't the default delay be set by
ufshcd_variant_ops.init()?

Thanks,

Bart.