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: <8f52b5a3-6104-9659-b60b-4d57007c1efe@quicinc.com>
Date: Tue, 7 Oct 2025 17:10:50 -0700
From: "Bao D. Nguyen" <quic_nguyenb@...cinc.com>
To: Bart Van Assche <bvanassche@....org>,
        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>,
        "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 10/7/2025 9:19 AM, Bart Van Assche wrote:
> 
> 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()?
> 

I am also not sure if it is worth adding complexity to the driver using 
a kernel parameter for this particular case.
I can try Bart's suggestion to override the default value with the 
platform driver init, or drop the change trying to reduce the sleep time 
from 5ms to 2ms.

Thanks, Bao

> Thanks,
> 
> Bart.