linux-kernel - Re: [PATCH v6 1/6] scsi: ufs: Add "wb_on" sysfs node to control WB on/off

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Date:   Tue, 19 Jan 2021 12:00:11 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Bean Huo <huobean@...il.com>, alim.akhtar@...sung.com,
        avri.altman@....com, asutoshd@...eaurora.org, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, stanley.chu@...iatek.com,
        beanhuo@...ron.com, bvanassche@....org, tomas.winkler@...el.com,
        cang@...eaurora.org
Cc:     linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 1/6] scsi: ufs: Add "wb_on" sysfs node to control WB
 on/off

On 19/01/21 11:33 am, Bean Huo wrote:
> On Tue, 2021-01-19 at 09:01 +0200, Adrian Hunter wrote:
>> On 18/01/21 10:10 pm, Bean Huo wrote:
>>> From: Bean Huo <beanhuo@...ron.com>
>>>
>>> Currently UFS WriteBooster driver uses clock scaling up/down to set
>>> WB on/off, for the platform which doesn't support
>>> UFSHCD_CAP_CLK_SCALING,
>>> WB will be always on. Provide a sysfs attribute to enable/disable
>>> WB
>>> during runtime. Write 1/0 to "wb_on" sysfs node to enable/disable
>>> UFS WB.
>>
>> Is it so, that after a full reset, WB is always enabled again?  Is
>> that
>> intended?
> 
> Hello Adrian
> Good questions. yes, after a full reset, the UFS device side by default
> is wb disabled,  then WB will be always enabled agaion in
> ufshcd_wb_config(hba). but, for the platform which
> supports UFSHCD_CAP_CLK_SCALING, wb will be disabled again while clk
> scaling down and enabled while clk scaling up.
> 
> Regarding the last question, I think OEM wants to do that. maybe they
> suppose there will be a lot of writing after reset?? From the UFS
> device's point of view, the control of WB is up to the user.

If it is by design enabled after reset, then perhaps it should be mentioned
in the sysfs documentation.