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Subject: Re: [PATCH v6 1/6] scsi: ufs: Add "wb_on" sysfs node to control WB
 on/off
To:     Bean Huo <huobean@gmail.com>, alim.akhtar@samsung.com,
        avri.altman@wdc.com, asutoshd@codeaurora.org, jejb@linux.ibm.com,
        martin.petersen@oracle.com, stanley.chu@mediatek.com,
        beanhuo@micron.com, bvanassche@acm.org, tomas.winkler@intel.com,
        cang@codeaurora.org
Cc:     linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20210118201039.2398-1-huobean@gmail.com>
 <20210118201039.2398-2-huobean@gmail.com>
 <0a9971aa-e508-2aaa-1379-fb898471a252@intel.com>
 <fabf0e83387f6155efea521a15b00bb1225d35a4.camel@gmail.com>
From:   Adrian Hunter <adrian.hunter@intel.com>
Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki,
 Business Identity Code: 0357606 - 4, Domiciled in Helsinki
Message-ID: <9ad2cf1a-68df-47ef-9fe7-01954d2d6181@intel.com>
Date:   Tue, 19 Jan 2021 12:00:11 +0200
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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@micron.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.