linux-kernel - Re: [PATCH v2 2/2] scsi: ufs: core: Replace hard coded vcc-off delay with a variable

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Message-ID: <ea706279-3c74-bd0e-453a-d635ca0c82d9@quicinc.com>
Date: Mon, 13 Oct 2025 12:34:53 -0700
From: "Bao D. Nguyen" <quic_nguyenb@...cinc.com>
To: Peter Wang (王信友) <peter.wang@...iatek.com>,
        "quic_cang@...cinc.com" <quic_cang@...cinc.com>,
        "martin.petersen@...cle.com"
	<martin.petersen@...cle.com>,
        "adrian.hunter@...el.com"
	<adrian.hunter@...el.com>,
        "bvanassche@....org" <bvanassche@....org>,
        "quic_nitirawa@...cinc.com" <quic_nitirawa@...cinc.com>,
        "avri.altman@....com" <avri.altman@....com>
CC: "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "beanhuo@...ron.com" <beanhuo@...ron.com>,
        "neil.armstrong@...aro.org"
	<neil.armstrong@...aro.org>,
        "alim.akhtar@...sung.com"
	<alim.akhtar@...sung.com>,
        "James.Bottomley@...senPartnership.com"
	<James.Bottomley@...senPartnership.com>,
        "ebiggers@...nel.org"
	<ebiggers@...nel.org>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] scsi: ufs: core: Replace hard coded vcc-off delay
 with a variable

On 10/12/2025 8:58 PM, Peter Wang (王信友) wrote:
> On Thu, 2025-10-09 at 13:10 -0700, Bao D. Nguyen wrote:
>>
>> +       /*
>> +        * Most ufs devices require 1ms delay after vcc is powered
>> off before
>> +        * it can be powered on again. Set the default to 5ms. The
>> platform
>> +        * drivers can override this setting as needed.
>> +        */
>> +       hba->sleep_post_vcc_off = 5000;
>> +
>>
> 
> Hi Bao,
> 
> Since 2ms is sufficient for most devices, wouldn't it make
> sense to set the default value to 2ms?

Agree Peter. This was my preference as well.

> 
> 
>>          init_completion(&hba->dev_cmd.complete);
>>
>>          err = ufshcd_hba_init(hba);
>> diff --git a/include/ufs/ufshcd.h b/include/ufs/ufshcd.h
>> index 1d39437..ad49979 100644
>> --- a/include/ufs/ufshcd.h
>> +++ b/include/ufs/ufshcd.h
>> @@ -1140,6 +1140,8 @@ struct ufs_hba {
>>          int critical_health_count;
>>          atomic_t dev_lvl_exception_count;
>>          u64 dev_lvl_exception_id;
>> +
>> +       u32 sleep_post_vcc_off;
>>
> 
> The name sleep_post_vcc_off might be misunderstood as a
> status or a flag. I suggest changing it to a more explicit
> name, such as vcc_off_delay_ms.

Sure Peter. I will make the change.

Thanks, Bao

> 
> 
> Thanks
> Peter
> 
>